Conference Agenda

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Session Overview
Session
Mon: Poster Session & Social
Time:
Monday, 23/Sep/2019:
4:30pm - 6:00pm

Location: Tent in front of the castle/Schloss

Sessions: 1, 2a, 2b, 2e, 4d, 4e, 5b, 5g, 5h, 6b, 6c,7a, 7d, 8b, 9, 10a, 10b, 12a, 12b, 13a, 13c, 13d


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Presentations
Mon: 1
Topics: 1a) The Present is the Key to the Past – Reconstructing Early Earth Environments through Modern Analogues

Surviving the ferruginous Archean ocean – Assessing the potential toxicity of Fe2+ on basal Cyanobacteria in anaerobic conditions.

Achim Jan Herrmann, Michelle M. Gehringer

Technische Universität Kaiserslautern, Germany

The oxygenation of early Earth’s atmosphere ~2.4 Ga ago, known as the Great Oxygenation Event (GOE) was presumably caused by oxygenic photosynthesis from (proto-) Cyanobacteria. Previous the Archean oceans were anoxic with high levels of Fe2+ (40-120 µM Fe2+). However recent studies suggest that Fe2+ concentrations of >100 µM are toxic to modern, marine Cyanobacteria. This would have modulated their expansion in the ferruginous Archean oceans, necessary for the GOE. Studies to date have focused on closed systems with elevated CO2, allowing the build-up of O2. This study investigated the potential toxicity of Fe2+ on two basal strains of cyanobacteria in an atmosphere representing the Archean, in both a closed and open culture system.

Pseudanabaena PCC7367 and Synechococcus PCC7336, were incubated under an anoxic, elevated CO2 atmosphere in buffered ASNIII Media with increasing Fe2+ concentrations (15 µM, 120 µM and 600 µM). The cultures were monitored for chlorophyll a and Fe2+/ Fe3+ concentrations for 21 days. Additionally the production of O2 in the closed system was measured at the beginning and middle of the light cycle. Mid and late logarithmic cultures were assessed for respiration (CTC), viability (SYTOX Green) and Fe3+ precipitation using fluorescence microscopy. Media was assessed for dissolved CO2, nitrate and phosphate content.

While the closed system controls indicated a similar Fe2+ toxicity response to that seen in the literature, the cultures grown in an open system showed interesting deviations in Fe3+ accumulation and growth morphologies.

This study emphasises the influence of experimental design and importance of using different strains in investigating ecological trends, especially during the period leading up to the GOE.



Mon: 2
Topics: 1a) The Present is the Key to the Past – Reconstructing Early Earth Environments through Modern Analogues

Triple oxygen isotope study of manganese formations as a proxy for the triple oxygen isotope composition of Precambrian air O2

Sukanya Sengupta1, Andreas Pack1, Sebastian Viehmann2

1Department of Isotope Geology, Georg-August-Universität-Göttingen, Germany; 2Department of Geodynamics und Sedimentology, Universität Wien, Austria

The great oxidation event, recorded by the absence of mass independent fractionation of sulphur isotopes in marine sediments, sets the time for the advent of biologically mediated free oxygen in the oceans and the atmosphere [1]. The triple oxygen isotope composition of molecular O2 in the atmosphere is a tracer for global bio-productivity [2] and ancient pCO2 in the atmosphere [3]. Here, we attempt to reconstruct the triple isotope composition of Precambrian atmospheric O2 by means of analysis of Mn-rich iron formations.

Only few lithospheric materials bear signatures of atmospheric O2. Sedimentary sulphates [3] and cosmic spherules [4] contain oxygen originally derived from air O2. Also aqueous Mn-IV-oxides can contain a portion of oxygen originally derived from air O2 [5]. Laboratory experiments showed that 30-50% of oxygen in laboratory precipitated manganese-IV-oxides derived from molecular O2 dissolved in water.

We study the detrital-poor iron formation of the Neoproterozoic Urucum iron and manganese formation in the Santa Cruz Formation, Brazil [6]. Drill core samples from neither the Mn-rich nor the Fe-rich layers have evidence of metamorphic or hydrothermal overprints [6]. We will analyze triple oxygen isotope compositions of the shallow water Mn-oxides in the Urucum Fe-Mn-formation and compare these data to modern analogues. Our results will be discussed with respect to Precambrian pCO2 and global bioproduction rates. We will highlight the use of triple oxygen isotopes in Precambrian Mn-oxides for calculating the triple oxygen isotope of Precambrian air O2.

[1] Farquhar et al. (2000) Science 289, 756-758.

[2] Luz et al. (1999) Nature 400, 547-550.

[3] Bao et al. (2008) Nature 453, 504-506.

[4] Pack et al. (2017) Nat. Comm. 8, 15702.

[5] Mandernack et al. (1995) GCA 59, 4404-4425.

[6] Viehmann et al. (2016) Precamb. Res. 282, 74-96.



Mon: 3
Topics: 2a) Petrology, volcanism and surface processes on terrestrial bodies

Formation of sulfide phases on the surface of Mercury by reactions with reducing high temperature gases

Christian J. Renggli1, Stephan Klemme1, Andreas Morlok2, Iris Weber2, Harald Hiesinger2

1Institut für Mineralogie, Universität Münster, Germany; 2Institut für Planetologie, Universität Münster, Germany

Sulfur is abundant on the surface of Mercury with average concentrations of 4 wt. % [1]. The sulfur on Mercury’s surface has likely volcanic origins and may have been redistributed by explosive eruptions and impact events. In these processes, silicate materials were exposed to a hot S-rich gas phase at a very low oxygen fugacity of 4-5 fO2 log units below the iron-wüstite (IW) buffer [2].

We conduct experiments reacting a reducing sulfur-rich gas with synthetic basalt glasses. These glasses have compositions representative of Mercury terranes, including the high-Mg and high-Al regions, as well as the low-Mg northern volcanic plains [3]. We expose polished glass chips to a gas mixture of CO and SO2 at 800 °C for 24 h, corresponding to a fO2 of IW-2 to IW-5. This gas-solid reaction results in the formation of a coating similar to the reaction between SO2 and basaltic glasses [4]. In addition to conventional mineralogical and chemical analysis (SEM, Raman), the resulting coatings are characterized using diffuse reflectance FTIR spectroscopy in the mid-infrared from 2.5-18 µm. The obtained spectral data will be used to interpret remote sensing data from the MERTIS spectrometer (Mercury Radiometer and Thermal Infrared Spectrometer) onboard the BepiColombo (ESA/JAXA) mission to Mercury [5]. The comparison of the spectra will allow testing of our hypothesis on high-temperature gas-solid alteration of the surface of Mercury by reduced S-rich gases.

In addition to the experiments, we conduct Gibbs free energy minimization calculations. The dominant S-bearing gas species in a C-O-S gas mixture at Mercury conditions are CS2 and COS. The rock forming minerals forsterite, anorthite and diopside react in such a gas phase at 800 °C and IW-5 to form the sulfides CaS and MgS. Similarly, Na-bearing silicates react to form Na2S and Na2S2. We suggest that proposed sulfides on the surface of Mercury formed via gas-solid reactions.

[1] Nittler et al. (2011) Science 333, 1847-1850. [2] Zolotov M.Y. (2011) Icarus 212, 24-41. [3] Vander Kaaden et al. (2017) Icarus 285, 155-168. [4] Renggli et al. (2018) Rev. Mineral. Geochem. 84. [5] Hiesinger et al. (2010) Planet. Space Sci. 58, 144-165.



Mon: 4
Topics: 2a) Petrology, volcanism and surface processes on terrestrial bodies

Excimer Laser Experiments on Mixed Silicates Simulating Space Weathering

Iris Weber1, Andreas Morlok1, Marcel Heeger2, Thorsten Adolphs2, Maximilian P. Reitze1, Hiesinger Harald1, Karin E. Bauch1, Aleksandra N. Stojic1, Heinrich F. Arlinghaus2, Jörn Helbert3

1Westfälische Wilhelms Universität, Institut für Planetologie, 48149 Münster, Germany; 2WWU, Physikalisches Institut, 48149 Münster, Germany; 3DLR, Institut für Planetenforschung, 12489 Berlin, Germany

Here we present near and mid-infrared spectra of olivine-pyroxene mineral mixtures irradiated with a pulsed ArF UV excimer laser. Our experimental set-up simulates micrometeorite bombardment as one possible source of space weathering [1,2]. The subdued transparency feature of the irradiated samples indicates grain coarsening upon irradiation. Furthermore, the obvious darkening of the irradiated sample surface might be caused by agglutinate formation.

Petrographic and light microscope images confirmed the pure character of the sample crystals used for laser experiments. Reflectance infrared (IR) spectra obtained of olivine (Ol), pyroxene (Px), and mixtures of olivine and pyroxene with 70/30 and 30/70 (in weight %, grain size fractions: 63 – 125 µm) were compared with data of a spectral unmixing program for silicates of the same chemical composition. Results for these mixtures is in good agreement with the original sample mixtures [3]. Olivine and pyroxene show typical Christiansen Feature (CF) and Reststrahlen bands (RB) for these silicates [4]. The Ol70/Px30 mixture shows a significant blue shift of the CF. We observe a new RB shoulder at 9 µm and a peak split of the original olivine RB at 10.6 µm. The RB shoulder at 11.3 µm morphs into a separate RB feature. The CF of the Px70/Ol30 mixture shifted to higher wavelengths similar to the former pyroxene RB at 10.4 µm with a red shift to 10.5 µm and a significantly higher reflectance. It is remarkable that the olivine rich mixture exhibits more of the genuine olivine RBs than pyroxene in the pyroxene rich mixture. Results of IR investigations in vacuum on the same mineral mixtures but on pressed powder pellets before laser irradiation show a strong transparency feature (TF). After irradiation this TF disappears. The absence of this feature is indicative of grain coarsening. The TF could be used as a grain size tracer. The darkening of the sample surface is possibly also an effect of agglutination [5].

This work was partly supported by DLR grant 50 QW 1701 in the framework of the BepiColombo mission.

[1] Brunetto R. et al. Icarus 180, 546–554, 2006. [2] Loeffler et al. Meteoritics & Planetary Science, 51(2), 261-275, 2016. [3] Bauch K.E. et al. LPSC 50th, #2521, 2019. [4] Salisbury J. W. in: Topics in Remote Sensing 4, 79 – 98, 1993. [5] Stojic A. et al. LPSC 49th, #2083, 2018.



Mon: 5
Topics: 2a) Petrology, volcanism and surface processes on terrestrial bodies

Mineralogy of the weigelt-scholle

Patrick Winkler

Martin-Luther-Universität, Germany

mineralogy of the „Weigelt-Scholle“

The „Weigelt-Scholle“ is a sedimentary block with a size of 14 x 3 m, which lays in the rhyolithic porphyr of the small mountain Galgenberg in Halle (Saale) Germany. The Weigelt-Scholle was a interesting objekt for many generations of scientists over 100 years. It was first discovered by Johannes Weigelt in 1906, who then became the eponym of the Weigelt-Scholle. Other scientists such as Ernst Haase, Max Schwab und Günter Krumbiegel also did researches with the block in the first half of the 20th century. They focused on the formation of the subvolcanos in Halle and the surrounding areas.

The rhyolith oft he Galgenberg takes place for 300 Ma ago, as the supercontinent Pangäa began to falling into pieces. This resulted in crustal deformations in Europe, and hot magma began to rise into the upper continental crust. This hot magma intruded into sedimentary layers, which were formed in central europe. During this time, central Europe was divided into two regions; The Northern Perm Basin and the Southern Perm Basin. The todays´ Galgenberg and Halle are now located, where Southern Perm Basin used to be. As the magma rose the sedimentary layers above it got assimilated, however some parts of the layers – such as the block of the Weigelt-Scholle - broke off and fell into the magma. The block of the Weigelt-Scholle strikes SE-NW and has a dipangel of ca. 35° to the north. It is generally made of fine klastica like fine sandstone and siltstone. Furthermore, it also contains tuff breccia. The content of the bachelor thesis is to take some samples and creat some thinsections to determine the mineralogy of the Weigelt-Scholle. Additionally, the thesis aims to creat some profiles as well as to illustrates genesis of the Weigelt-Scholle.

The Weigelt-Scholle consists of three diverent lithologies.The first lithology was an arcosic sandstone with ca. 85% xenomorphic quarz, ca. 10% plagioclase and lots of exogenous inclusions. There were also orthoklases that were sericitized, thus, a lot of opaque dispersed hematite.

The second lithology is a reddish siltstone with lots of bright reddish round inclusions. These inclusions were once roots. In this sample, there was also a lot of dispersed hematite.

The third lithology is a red tuff with a phorphyric texture. The fourth sample is the porphyric rhyolith, which is called Hallescher Porphyr.



Mon: 6
Topics: 2b) High-spatial resolution studies of small-scale and complex extraterrestrial and terrestrial samples

Modal abundances of coarse-grained (>5 µm) components within CI-chondrites and their individual clasts

Julian Alfing1,2, Markus Patzek1, Addi Bischoff1

1Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, D-48149 Münster, Germany; 2Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149 Münster, Germany

The CI chondrites are complex breccias and their degree of brecciation among the studied rocks is decreasing in the sequence: Orgueil > Ivuna > Alais ~ Tonk. Considering the CI chondrite bulk rocks in general, various values for the modal abundance of matrix (95-100 vol% [1-3]) and the accompanied mineral constituents are given. Here, we discuss the determined modal abundance of phases >5 µm in the CI chondrites Orgueil, Ivuna, Alais, and Tonk. If this cut-off grain-size is used to distinguish between matrix and coarse-grained constituents, then, the modal abundance of the minor phases magnetite, pyrrhotite, carbonate, olivine, and pyroxene is 6 vol% in total. These phases are embedded within the fine-grained, phyllosilicate-rich matrix making up 94 vol%. The values vary slightly from meteorite to meteorite. Considering the four studied chondrites the most abundant phase is magnetite (4.3 vol%) followed by pyrrhotite (~1.1 vol%) and carbonates (~0.5 vol%). Phosphate, olivine, and pyroxene are also rare constituents. However, the CI-breccias contain clasts with highly-variable modal abundances. Therefore, we also studied individual clasts with the highest abundance of specific coarse-grained phases. In this respect, in Orgueil a fragment with 21.5 vol% of magnetite was found. We also detected a phosphate-rich fragment in the same meteorite having 31.8 vol% phosphate, whereas in Ivuna an individual clast with 21.5 vol% carbonates was detected. Such a heterogeneity of CI chondrites was earlier described (e.g. [4,5]). Thus, since the CI-composition is used as a standard for comparison in geochemistry, one has to consider that sufficiently large sample masses are required to obtain a representative CI-composition. Small aliquots with one dominating lithology may deviate significantly from the suggested CI-composition used as a standard.

[1] Weisberg M. K. et al. 2006. Meteorites and the Early Solar System II. Univ. of Arizona, Tucson, 19–52. [2] Scott E. R. D. and Krot A. N. 2014. Treatise on Geochemistry (Second Edition), Elsevier, 65-137. [3] Alexander C.M. O´D. 2019. Geochim. Cosmochim. Acta 254, 277-309. [4] Endress M. et al. 1996. Science 379, 701–703. [5] Morlok A. et al. 2006. Geochim. Cosmochim. Acta 70, 5371-5394.



Mon: 7
Topics: 2b) High-spatial resolution studies of small-scale and complex extraterrestrial and terrestrial samples

SORTED STONE CIRCLES ON SVALBARD – AN ANALOG STUDY FOR MARS

Sandra Buer1, Harald Hiesinger1, Dennis Reiss1, Ernst Hauber2, Andreas Johnsson3, Hannes Bernhardt4

1Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany; 2DLR-Institut für Planetenforschung, Rutherfordstr. 2, 12489 Berlin, Germany; 3Univ. of Gothenburg, Box 100 SE-405 30 Gothenburg, Sweden; 4Arizona State University, School of Earth and Space Exploration, 550 East Tyler Mall Bateman Physical Sciences Center F-Wing Room F506 Tempe, AZ 85287-1404, USA

Introduction: On Mars, sorted stone circles (SSC), one type of patterned ground, were observed in several locations [1-4]. Balme et al. [2] proposed that these Martian SSCs might share the same origin as SSCs on Earth, i.e. sorting by repeated freeze-thaw cycles due to an active layer. To decipher the formation mechanisms of SSCs on Mars, we studied analog SSCs on Earth.

Western Spitsbergen in the high-arctic archipelago of Svalbard was chosen as study area, because there are well-developed SSCs that formed in a cold-climate environment that display a wide range of Mars-analogue periglacial landforms [3]. The study area is located north-west of the research station Ny Ålesund at the tip of the Brøggerhalvøya peninsula called Kvadehuksletta [1].

Methods: To investigate the SSCs on Svalbard, we measured the topography (only 2016) and the soil temperatures, sampled vertical profiles and took areal pictures [4]. The grain size distribution, the soil moisture and the soil organic carbon (SOC) were analyzed in the laboratory [4].

Results: Three SSCs were examined during the field work in 2016 (16SC2 and 16SC4) and 2017 (17SC1). The grain size analyses show that the walls (type 1) have coarser material than the inner domain (type 2–4). At the surface, soil moisture in the fine material is higher than in the coarser walls. In the circles sampled in 2014 [1] and 2016, we do not observe a pattern of SOC values that is reminiscent of a convection-like movement of particles in the inner domain as found by [5].

Discussion/Conclusions: We hypothesize that in fall, thawed stone circles likely freeze top-down. In such a scenario, the cooler, drier and permeable coarser-grained walls might conduct cold air downwards, so that the walls and the parts adjacent and beneath the walls freeze before the more wet central interior of the SSC. If this working hypothesis is correct, a convection-like movement of soil as proposed by [5] might be an oversimplification. Neither the distribution of grain size and soil moisture, nor the SOC strongly support a convection-like movement.

References: [1] Hiesinger H. et al. (2017) LPSC 48th, Abstract #1164. [2] Balme M. R. et al. (2009) Icarus, 200, 30-38. [3] Hauber E. et al. (2011) Geol. Soc. London Spec. Pub. 356, 111-131. [4] Buer S. et al. (2019) LPSC 50th, Abstract #2313. [5] Hallet B. and Prestrud S. (1986) Quat. Res., 26, 81-99.



Mon: 8
Topics: 2b) High-spatial resolution studies of small-scale and complex extraterrestrial and terrestrial samples

The Multi-Temporal Database of Planetary Image Data (MUTED): A Web-Based Tool to Study Surface Changes and Processes on Dynamic Mars

Thomas Heyer1, Harald Hiesinger1, Dennis Reiss1, Jan Raack1, Ralf Jaumann2

1Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Germany; 2German Aerospace Center (DLR), Berlin, Germany

The Multi-Temporal Database of Planetary Image Data (MUTED) is a web-based tool to support the identification of surface changes and time-critical processes on Mars. The database enables scientists to quickly identify the spatial and multi-temporal coverage of orbital image data of all major Mars missions. Since the 1970s, multi-temporal spacecraft observations have revealed that the martian surface is very dynamic [e.g., 1]. The observation of surface changes and processes, including eolian activity [e.g., 2], mass movement activities [e.g., 3], the growth and retreat of the polar caps [e.g., 4], and crater-forming impacts [5] became possible by the increasing number of repeated image acquisitions of the same surface areas. Today more than one million orbital images of Mars are available [6]. This increasing number highlights the importance of efficient and comprehensive tools for planetary image data management, search, and access. MUTED is accessible at http:muted.wwu.de and will assist and optimize image data searches to support the analysis and understanding of short-term, long-term, and seasonal processes on the surface and in the atmosphere of Mars. In particular, images can be searched in temporal and spatial relation to other images on a global scale or for a specific region of interest. Additional information, e.g., data acquisition time, the temporal and spatial context, as well as preview images and raw data download links are available. Due to continuous data acquisition by spacecraft, the amount of image data is steadily increasing and enables further comprehensive analyses of martian surface changes.

[1] Sagan et al. (1972) Icarus, 17, 346-372. [2] Reiss et al. (2011) Icarus, 215, 358-369. [3] Dundas et al. (2015) Icarus, 251, 244-263. [4] Calvin et al. (2017) Icarus, 292, 144-153. [5] Daubar et al. (2013) Icarus, 225, 506-516. [6] Heyer et al. (2018) PSS, 159, 56–65.



Mon: 9
Topics: 2b) High-spatial resolution studies of small-scale and complex extraterrestrial and terrestrial samples

CLASSIFICATION OF 13 CM CHONDRITE BRECCIAS

Sarah Lentfort, Addi Bischoff, Samuel Ebert

WWU Münster, Germany

CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. These fragments are mixed together and lithified in a fine-grained matrix; however, the conditions of aqueous alteration are still controversial (e.g., [1-6]). In particular, this is the case considering the chronological relationship between aqueous alteration and brecciation. To quantify the degree of alteration, different classification schemes have been suggested (e.g., [5-6]).

In this study, individual fragments of 13 CM chondrite breccias have been investigated in detail. The alteration index of 90 fragments was determined based on the optical appearance and chemistry of their PCPs using the procedure suggested by [6]. An accurate subclassification can only be performed by obtaining the chemical composition of the PCPs considering the “FeO”/SiO2- and S/SiO2-ratios and the SiO2, FeO, and MgO contents. For certain clasts “FeO”/SiO2-ratios were significantly above the values of 2.9 ± 0.6 (subtype CM2.6 by [6]) and lead to the definition of some new subtypes (CM2.7-2.9). Samples free of well-defined clasts were also classified by the analyses of PCP objects randomly distributed throughout the sample (e.g., NWA 10907). On this basis the CM chondrites are classified as follows: LON 94101 (CM2.0-2.8, also containing CI clasts), ALH 85013 (CM2.0-2.8), ALHA 77306 (CM2.0-2.6), Banten (CM2.4-2.9), NWA 10907, 10908 (CM2.3-2.4), Maribo (CM2.4-2.6), Jbilet Winselwan (CM2.3-2.9), Cold Bokkeveld (CM2.0-2.8), Nogoya CM2.0-2.6), Murchison (CM2.4-2.9), Y-791198 (CM2.4-2.8), Santa Cruz (CM2.4-2.8). The study shows that the degree of aqueous alteration can vary from clast to clast within a single thin section and between thin sections. Consequently, the CM subtype classification based on the most abundant fragment-type as used by [6] is not appropriate for the classification of complex CM chondrite breccias. Therefore, an extended classification scheme from 2.0-2.9 that takes the brecciation and the degree of alteration into account is more precise and preferable.

References: [1] Fuchs L.H. et al. (1973) Smiths. Contrib. Earth Sci. 10:1-39. [2] Metzler K. et al. (1992) Geochim. Cosmochim. Acta 56: 2873-2897. [3] Bischoff A. (1998) Meteoritics & Planet. Sci. 33: 1113-1122. [4] Metzler K. (2004) Meteoritics & Planet. Sci. 39:1307-1319. [5] Browning L. et al. (1996) Geochim. Cosmochim. Acta 60: 2621-2633. [6] Rubin A.E. et al. (2007) Geochim. Cosmochim. Acta 71: 2361-2382.

Acknowledgement: We thank the DFG for support within the SFB-TRR 170 (subproject B05) and the Meteorite Working Group and Mike Zolensky (both Houston) and the NIPR (Tokio) for the loan of meteorite samples.



Mon: 10
Topics: 2b) High-spatial resolution studies of small-scale and complex extraterrestrial and terrestrial samples

A Chondrule Formation Experiment Aboard the ISS: Experimental Set-up and Test Experiments

Dominik Spahr1, Tamara E. Koch1, David Merges1, Anna A. Beck1, Oliver Christ1, Shintaro Fujita2, Philomena-T. Genzel1, Jochen Kerscher2, Miles Lindner1, Diego Menderos-Leber1, Fabian Wilde3, Wolfgang Morgenroth1, Frank E. Brenker1, Björn Winkler1

1Goethe University Frankfurt, Germany; 2HackerSpace FFM e. V., Oberursel, Germany; 3Helmholtz-Zentrum Geesthacht, HZG Outstation at DESY in Hamburg, Hamburg, Germany

The formation of chondrules is one of the most enigmatic processes in planetary science. The EXCISS experiment (Experimental Chondrule formation aboard the ISS) was developed in order to investigate if chondrule formation via “nebular lightning” [1–5] is a viable process. At conditions of long-term micro gravity synthetic forsterite (Mg2SiO4) particles were repeatedly exposed to electrical discharges with the aim to observe if these particles melt and fuse under these conditions. EXCISS was launched with Cygnus NG-10 on November 17th, 2018 and was carried in December 2018 and January 2019 aboard the ISS. Here, we will present the experimental set-up of the ISS based experiment together with the first results of the experiments in space.

The experimental set-up is mounted in a 1.5 U NanoRacks NanoLab with a size of approx. 10 × 10 × 15 cm3. Forsterite particles (80 – 120 μm) were levitating in aglass sample chamber, filled with Ar at 100 mbar pressure, where they were subjected to electrical arcs. The behavior of the particles in micro gravity was documented with a video camera. We complemented these experiments by laboratory-based discharge experiments on Earth.

The experiments aboard the ISS were successfully completed. We performed about 80 arc discharges. The video documentation shows that some dust particles initially stuck on the walls and the electrode. Furthermore, many particles formed irregular shaped agglomerates levitating in the sample chamber and thus became precursors well suited for the discharge experiments. These agglomerates were attracted by the charged electrodes. After the discharge experiments, we observe that the arc discharges led to changes in the particle size and shape. The capsule return is planned with SpaceX CRS17 scheduled for end of May 2019 and after sample return, we will analyze these experimental products in detail.

Acknowledgments:
We gratefully acknowledge the HackerSpace FFM, Rainer Haseitl, Solveigh Matthies and the IAP Frankfurt for technical support. We are grateful for financial support by the DFG (Wi1232), the Dr. Rolf M. Schwiete Stiftung, the BMBF (05K16RFB), the German Aerospace Center (DLR), BIOVIA, ZEISS, DreamUp, NanoRacks and Nordlicht GmbH. We acknowledge DESY. Parts of this research were carried out at PETRA III.

References:
[1] Whipple F. L. (1966) Science 153:54–56.
[2] Horányi, M. et al. (1995) Icarus 114:174–185.
[3] Desch S. J. and Cuzzi, J. N. (2000) Icarus 143:87–105.
[4] Johansen A. and Okuzumi A. (2018) Astronomy & Astrophysics A31:1–22.
[5] Güttler C. et al. (2008) Icarus 195:504–510.



Mon: 11
Topics: 2e) Recent advances in lunar science

Exploration of Icelandic lava caves and extrapolation to a semi-permanent Lunar habitat

Marjolein Daeter1, Marc Heemskerk1, Bernard Foing1,2,3

1VU Amsterdam, The Netherlands; 2ESTEC, ESA; 3ILEWG/EuroMoonMars

For the testing and planning of Lunar missions, it is important to find terrestrial locations comparable to The Moon. Current Moon-analogue bases, like HiSeas (Hawaii) and LunAres (Poland) rely on vast, man-made structures. Because bringing this much material to The Moon to build a semi-permanent settlement might not be feasible, a possible alternative is to use already existing structures in the Lunar subsurface. An example of these structures is lava caves.

Lava caves are long stretched, cylindrical cave structures, formed by the crystallization of a layer of rock around a lava flow. These cave systems have sporadic openings to the surface, making them relatively easy to access. But what makes the lava caves the most convenient, is that the temperature inside the caves is roughly the average surface temperature. For The Moon this would mean that the temperature is stable around -20°C. This is much less extreme and more stable than possible temperature variations on the Lunar surface, meaning less temperature adjustments would need to be made to create a habitable living environment. Secondly, caves also give protection against radiation and (micro)meteorites.

The reason that lava caves in Iceland would be a good analogue site, is that the Icelandic basalts are geochemically similar to basalts on The Moon. The low weathering rate on Iceland due to the cold climate also makes the geomorphology of the caves similar to what we expect of Lunar lava caves. Furthermore, the remoteness of the lava caves (1.5 hour drive from Reykjavik) and the difficult weather conditions, especially in winter, add to the suitability of this location to be a Moon-analogue site.

In September 2018, a team or researchers visited three cave systems in Iceland. The Stefanshellir lava cave was selected for a Lunar analogue base, because of its remote location and long lava tubes. A campaign to Iceland in August this year will cover exploration of the cave systems with drones and mapping of the surrounding area. Furthermore, the first simulations of analogue Lunar missions will be conducted. This will include equipment testing, geological and glaciological research as well as evaluation of psychological and protocol factors.

A Moon-analogue habitat in lava caves in Iceland can be a real addition to already existing analogue-sites because it is very possible that our first semi-permanent base will be using already existing structures in or on the (sub)surface of The Moon, and perhaps in the future, even Mars.



Mon: 12
Topics: 2e) Recent advances in lunar science

The ESA-JAXA-CSA-NASA Joint Study HERACLES on Returning to the Moon

Harald Hiesinger1, Markus Landgraf2, William Carey2, Yuzuru Karouji3, Tim Haltigin4, Gordon Osinski5, Urs Mall6, Ko Hashizume7

1Westfälische Wilhelms-Universität Münster, Germany; 2European Space Agency (ESA), Directorate of Human Spaceflight and Robotic Exploration Programmes; 3Japan Aerospace Exploration Agency (JAXA), Space Exploration System Technology Unit; 4Canadian Space Agency (CSA); 5University of Western Ontario, Centre for Planetary Science and Exploration; 6Max-Planck Institut für Sonnensystemforschung; 7Ibaraki University, Dept. of Earth Science

Introduction: Several space agencies have recognized the scientific (and strategic) benefits of returning to the Moon as well as the opportunities the Moon offers for testing hardware and operational procedures for the exploration and utilization of space beyond Low Earth Orbit. In this context, the Human Enhanced Robotic Architecture Capability for Lunar Exploration and Science (HEREACLES) is an ESA-led international effort to prepare for the return of humans to the Moon and to provide opportunities for unprecedented science utilizing the lunar Gateway. HERACLES is a joint phase-A study of the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA), the Canadian Space Agency (CSA), and NASA.

Mission Concept: The key objectives of HERACLES include: (1) Preparing the return of humans by implementing, demonstrating, and certifying technologies for human lunar landing, surface operations, and return; (2) Create opportunities for science, including sample return; (3) Gain scientific and exploration knowledge, particularly on potential resources; and (4) Create opportunities to demonstrate and test technologies and operational procedures for future Mars missions. HERACLES will consist of the Lunar Descent Element (LDE), which will be provided by JAXA, the ESA-built Interface Element that will house the Canadian rover, and the European Lunar Ascent Element (LAE) that will return the samples to the lunar Gateway. The 330 kg rover will be powered by a radioisotope power system that will enable the rover to drive more than 100 km and to survive lunar night. The rover will collect samples along a ~35 km long traverse from about ten individual sampling stations and will return them to the LAE. The rover will be equipped with a suite of scientific instruments that will allow us to comprehensively study the sampling locations and the context of the samples, as well as the geology along the traverse. The international Science Definition Team (iSDT) is currently discussing an appropriate instrument suite, which will most likely include cameras, spectrometers, a laser reflector, and potentially some geophysical instruments. During the surface mobility demonstration phase, the rover will go on a >100 km long traverse. The iSDT is evaluating a suite of potential landing sites, guided by the recommendations of the 2007 NRC report and several subsequently published documents. The list of potential landing sites includes the Schrödinger basin, the Moscoviense basin, Copernicus crater, Jackson crater, and some young basalts in the Flamsteed region.



Mon: 13
Topics: 2e) Recent advances in lunar science

Geology and ages of the landing sites: Apollo 11, Apollo 12 and Apollo 17

Wajiha Iqbal, Harald Hiesinger, Carolyn van der Bogert

Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany

The lunar cratering chronology [1,2] is widely used to derive absolute model ages (AMAs) of geological units on the Moon [3], as well as other terrestrial planetary bodies throughout the Solar System. With new datasets, the accuracy of the chronology can be tested and updated via reexamination of the calibration points from the landing sites [4,5,6], which consist of both crater size-frequency distribution measurements and sample ages.

Using data including Lunar Reconnaissance Orbiter Camera (LRO) Narrow-angle Camera (NAC) and Wide Angle Camera (WAC) frames, digital terrain models (DTM) derived from LOLA/SELENE merged data, as well as spectral data collected by Clementine, M3, and Kaguya Mineral Imager, we are producing new detailed geological maps around the Apollo landing sites. The geological units are defined via albedo, relief, and spectral differences. The new geological maps were used to identify homogeneous areas with crater densities characteristic for the sampled materials. We also used high-resolution LROC NAC and the LRO NAC-derived DTMs, to measure crater size-frequency distributions (CSFD) and determine N(1) values (i.e. the cumulative number of craters with diameters ≥1 km) for the different geological units around the landing sites.

We correlated the updated radiometric ages of well-studied Apollo samples [7] with the newly measured N(1) values, to improve the calibration points for the lunar chronology curve [1]. We gained several calibration points representing the geological units including mare units, and crater materials around the landing sites Apollo 11, 12, and 17. The new, improved calibration points gained from the geological units around the landing sites supports the validity of the lunar chronology curve [1].

[1] Neukum(1983) Habil. thesis, U. of Munich. [2] Neukum et al. (2001) Space Sci. Rev. 96, 55. [3] Hiesinger, et al. (2000) JGR 105, 29239. [4] Iqbal, et al (submitted 2019) Icarus. [5] Iqbal, et al (2018) LPSC 49, 1002. [6] Iqbal, et al (2018) LPSC 50, 1005. [7] Stöffler, et al. (2006) RMG 60, 519.



Mon: 14
Topics: 2e) Recent advances in lunar science

Mare Moscoviense: A site for future lunar missions

Sascha Mikolajewski, Harald Hiesinger, Carolyn H. van der Bogert

Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

Introduction: Exploration of the Moon has generated increasing international interest over the last few years. Several studies [1-11] have used multispectral data and images to gain insights into the timing and duration of mare volcanism on the Moon. Clementine [1, 2] and Kaguya [3-5] spectral data, have been used to document compositional differences in lunar rocks and regolith. In this work, we use recent lunar datasets for Mare Moscoviense, on the lunar farside, to generate a new geological map and examine possible landing locations for future missions.

Data/Methods: Within ArcGIS, we used Kaguya Mineral Maps [3], Clementine FeO and TiO2 multispectral data [1], and Lunar Reconnaissance Orbiter Camera (LROC) datasets [7] to define morphological and compositional geological units within Mare Moscoviense. Using digital terrain models [8], slope maps, and LRO Diviner rock abundance values [6], we examined possible safe landing sites and select locations for scientific research.

Results: Inside Mare Moscoviense, there are three volcanic flows with different spectral compositions [9 and this work]. The slope map derived from the LROC image digital elevation model indicates that the basin floor is very flat. The rock abundance map of the targeted region indicates that the southeastern and eastern part of the basin has the lowest abundance of rocks.

Discussion/Conclusions: On the lunar farside, mare volcanism occurs on a smaller scale than compared to the nearside as shown by [10, 11, and this work]. The southeastern and eastern volcanic flows show the lowest abundance of rocks compared to the other flows. The eastern flow provides access to older impact craters that may be related to the original basin floor. The evaluation of the rock abundance values also showed that the eastern part of Mare Moscoviense is the most promising part for scientific research with respect to lander and rover safety.

References: [1] Lucey et al. (1998) JGR, 103, 3679-3699. [2] Chevrel. et al. (2000) JGR. 107, NO. E12, 5132. [3] Lemelin et al. (2016) 47th LPSC #2994. [4] Morota et al. (2009) GRL, 36, L21202. [5] Morota et al. (2011) Earth Planets Space, 63, 5-13. [6] Bandfield et al. (2011) Icarus, 116. [7] Sato et al. (2017) Icarus, 296, 216-238. [8] Scholten et al. (2012) JGR, 117(3). [9] Kramer et al. (2008) JGR, 113. [10] Pasckert et al. (2015) Icarus, 257, 336-354. [11] Pasckert et al. (2018) Icarus, 299, 538-562.



Mon: 15
Topics: 2e) Recent advances in lunar science

Lunar gravity: Impact processes inform the density structure of the mare crust

Gregory A. Neumann1, Sander J. Goossens2, Ariel N. Deutsch3, James W. Head3

1Solar System Exploration Division, NASA Goddard, Greenbelt, MD, United States of America; 2CRESST, University of Maryland Baltimore County, USA; 3Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA

Recent improvements in Gravity Recovery and Interior Laboratory (GRAIL) modeling (Goossens et al., 2018; 2019 submitted) allow a closer look at the laterally variable density structure of the nearside lunar mare regions. Spectral analyses of gravity in highland regions exhibit nearly perfect correlation with topography at spherical harmonic degrees from 250 to beyond 900, corresponding to spatial scales < 12 km, but in most of the nearside mare and the interior regions of the farside South Pole-Aitken basin the correlations drop off substantially. Since these scales are only influenced by the shallow crustal density structure, we employ relatively fresh impact craters in the range of 3-5 km depth and16-130 km diameter as probes of mare density. Modeled gravity anomalies of these craters suggest an increase in density of 25-30% averaged over the crater depths between the excavated mare flow layers and the surrounding highlands. We interpret these results in the light of enigmatic quasi-circular gravity anomalies, in the southwestern Procellarum region for example, that have been suggested to arise from some combination of buried craters, volcanic intrusion and/or mantle uplift and crustal thinning.



Mon: 16
Topics: 2e) Recent advances in lunar science

Geological Mapping of the South Pole-Aitken Basin - A Progress Report

Claudia Pöhler1, Harald Hiesinger1, Mikhail A. Ivanov2, Cedric Rueckert1, Carolyn H. van der Bogert1

1WWU Münster, Germany; 2Vernadsky Institute, RAS, Russia

The South Pole-Aitken basin (SPA), situated on the lunar farside and centered at 53°S 169°W, is the largest and oldest basin [1,2] on the Moon. Due to its morphological appearance it is argued that the SPA basin formed within an already solidified lunar crust [3]. Therefore, the time of SPA formation gives valuable information on the evolution of the lunar crust. The large scale of the impact led to the hypothesis of it penetrating the crust, potentially exposing lunar mantle material within the SPA [e.g., 4]. Thus, it might be possible to observe lunar mantle material or lower crustal material excavated by the impact event [e.g., 5]. Recently, the SPA has been the focus of several ongoing and upcoming missions [6-9]. On January 2, 2019, Chang’e 4 performed the first ever soft-landing on the farside of the Moon in Von Kármán crater (175.9° E and 44.8° S) [7].

This project is part of the PLANetary MAPping project, a Horizon2020-COMPET4 project, aiming to develop a professional European network for geological mapping. In the scope of PLANMAP we are creating a geological map of the SPA based on photogeology and absolute model ages derived by crater size-frequency distribution measurements. In the study area two major classes of landforms can be observed: (1) impact craters and related materials and (2) plains forming material. Impact craters and their related material are divided into further classes by different stages of degradation, allowing for relative age determinations. The plains forming material can represent volcanic activity as well as impact cratering e.g. by emplacement of distal ejecta from impact craters/basins. This map is an extension of the map by [8].

[1] Wilhelms (1987) USGS SP-1348, 302. [2] Hiesinger et al. (2012) LPSC 43, 2863. [3]Stuart-Alexander(1978)USGSMapI-1047,1978. [4] Melosh et al. (2017) Geology 45, 1063-1066. [5] Yamamoto et al. (2010) Nature Geoscience 3, 533-536. [6] Hiesinger et al. (2018) LPSC 49, 2070. [7] Huang et al. (2018) JGR 123, 1684-1700. [8] Ivanov et al. (2018) JGR 123, 2585–2612. [9] Joliff et al. (2010) LPI Cont 1595, 3072.



Mon: 17
Topics: 4d) Latest Achievements in Scientific Ocean and Continental Drilling

Feather feature orientations in shocked granitic rocks of the Chicxulub crater: Implications for the formation of peak rings

Matthias Ebert, Michael Poelchau, Thomas Kenkmann

Albert-Ludwigs-Universität Freiburg, Department of Geology, Germany

The Chicxulub crater is the third largest impact structure on Earth, and the only known terrestrial crater with an unequivocal topographic “peak ring”. The recent drilling into Chicxulub's peak ring (IODP-ICDP Expedition 364, 2016) addresses several questions, including the nature and formational mechanism of peak rings [1]. In order to unravel its complex formational process we need to understand the heterogeneous deformation mechanisms that have occurred during cratering. Therefore, the new drill core provides a unique view into the deformation styles of a peak ring [1]. The sampled core reveals the occurrence of quartz grains showing shock-related feather features (FFs) within ~580 m of granitic basement rocks [2,3]. The orientation of these microstructural features is suggested to be controlled by the orientation of the principal axis of stress (σ1) within the shock wave, which indicates the propagation direction of the shock front [4]. Based on this FFs-model, we determined local σ1 orientations at different depth of the peak ring core in order to see if there is a consistent or interrelated orientation. This approach allows us to reconstruct rotational movements of the target rocks during cratering in general and peak ring formation in particular. Our σ1 data indicate that the basement rocks between ~750 and ~1200 mbsf behaved as a semi-coherent block that underwent an internal rotation or folding. The rotation axis is in NNO-SSW direction, i.e., concentric to the crater center, which emphasizes the connection between shock wave propagation and FFs formation. We could not find a trend for σ1 in samples below ~1200 mbsf. In this region, the peak ring shows extreme deformation that is characterized by a wide range of structures, including shear faults, zones of cataclasis, striated shear planes and dm-thick zones of foliated and crenulated mineral fabrics. The combination of these deformation processes may induce to a large number of small-scale rotational movements in the peak ring units, which is reflected by the chaotic σ1 orientations. This lower part of the peak ring core is interpreted as the main outward thrust zone active during imbrication of the peak ring.

[1] Morgan J. V. et al. (2016) Science, 354:878–882, [2] Poelchau M. H. et al. (2017) 48th LPSC, Abstract #1924, [3] Ferrière L. et al (2017) 48th LPSC, Abstract #1600, [4] Poelchau M. H. & Kenkmann T. (2011), JGR Solid Earth, 116(B2).



Mon: 18
Topics: 4d) Latest Achievements in Scientific Ocean and Continental Drilling

Deep Lake Sediment Sampling on Lake Constance using Hipercorig

Ulrich Harms1, Ulli Raschke2, Antje Schwalb2, Volker Wittig3, Thomas Wonik4, Martin Wessels5

1GFZ - German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany; 2Institute of Geosystems und Bioindication, Technische Universität Braunschweig, Langer Kamp 19c, 38106 Braunschweig, Germany; 3International Geothermal Centre, Hochschule Bochum, Lennershofstraße 140, 44801 Bochum, Germany; 4Leibniz-Institut für Angewandte Geophysik, Stilleweg 2, 30655 Hannover, Germany; 5Institut für Seenforschung der LUBW, Argenweg 50, 88085 Langenargen, Germany

The sediments in Lake Constance provide distinct paleo-environmental signals which so far could only be sampled down to about 11 m depth below lake bottom although more than 100 m infill is known from seismic lines. The well-defined and horizontally-bedded lacustrine sediments of the upper tenth of meters are most likely Holocene deposits that overlay deeper undisturbed late Glacial sediments. The access to such strata that often archive key information on climate and biological evolution is not only on Lake Constance but also globally in many lakes difficult and cost intensive. In order to overcome the problems in accessing deep lake layers we have developed a compact sediment coring and barge system and tested it on Lake Constance during a shake-down cruise in May and June 2019.

The Hipercorig consists of a modular barge and sediment piston coring system with a range of up to 200 m water depth for anchoring plus 100 m deep coring in 2 m sections. The key technology is i) a hydraulic power transmission that drives a down-the-hole hammer through a high-pressure pump, ii) a contamination free usage of lake water as hydraulic medium, and iii) a lightweight and complete modular design allowing for set-up and operation without heavy machinery. Hipercorig is equipped with an anchoring system, two service and safety boats and other auxiliary equipment transportable in four 20 ft standard containers. For operations on Lake Constance, an experienced coring crew of three was complemented by a science crew of two for the initial core handling.

The test on Lake Constance was performed in 204 m deep water 2 km SSW of Hagnau, Germany. The site is located close to the deepest part of this basin with best possible preservation of a continuous and undisturbed sediment record. Coring and core recovery results as well as a first assessment of the sediments recovered will be reported in this contribution. In addition, the test on Lake Constance included a first trial of geophysical downhole logging within a piston-cored borehole from Hipercorig.

Hipercorig is available for the science community at large. Costs for transport and personal have to be covered by individual project funds. The range of utilization comprises lakes and similar aquatic environments and also land sites such as bogs and alike. The Deutsche Forschungsgemeinschaft funded the acquisition and testing. The GESEP Consortium e.V. provides oversight to ensure safe operations and long-term availability.



Mon: 19
Topics: 4e) Archives of environmental changes throughout Earth history

The distribution of rare earth elements and yttrium (REY) between the truly dissolved, nanoparticulate/colloidal and suspended loads during high and low discharge in the Kalix and Råne Rivers, Northern Sweden

Nadine Elisabeth Weimar1, Katja Schmidt1,2, Erika Kurahashi1, Michael Bau1

1Jacobs University Bremen, Germany; 2BGR, Marine Resource Exploration, Hannover, Germany

Rivers play a major role for the trace element composition of the ocean. The following three different size fractions can be distinguished in river water: (i) suspended particles (>0.2 µm), (ii) nanoparticles and colloids (NPCs; 0.2 µm - 10kDa), and (iii) the truly dissolved fraction (<10kDa). Trace elements such as REY can be associated with all of these size fractions. As elements sorbed onto suspended particles and NPCs are removed from the water column during estuarine mixing, only the truly dissolved fraction reaches the ocean. However, detailed knowledge of the REY distribution between these different fractions is so far rather limited due to sometimes challenging ultrafiltration procedures.

We investigated the distribution of REY in two northern Swedish rivers, the Kalix and the Råne, during times of low river discharge (February 2017) and high river discharge (May 2019) with the aim to determine how the seasonal variation in two boreal rivers influences the REY distribution between the different size pools. This will help to better understand the role of NPCs in the transport of these particle-reactive elements into the oceans.

The Kalix and the Råne are two pristine rivers which are not regulated and which flow into the Baltic Sea. The catchment area of both rivers consists of only recently exposed granitic tills of Archean age. The Kalix River has a catchment area of 18,130 km2 and the Råne River a smaller one of 4207 km2. Boreal rivers often display flat shale-normalized REY patterns, but may also show strong seasonal changes [1]. Our REY results for the dissolved fraction (<0.2 µm) of the Kalix and the Råne rivers during low discharge also show such flat patterns together with a negative Ce anomaly. In marked contrast, the truly dissolved fraction shows a strong difference between the heavy and light REY (HREY and LREY, resp.), resulting in increasing HREY/LREY and Y/Ho ratios with decreasing filter pore size. In the dissolved fraction (<0.2 µm) of the Kalix River, 16-20% of LREY and 38-54% of HREY are bound to small organic NPCs between 1 kDa and 10 kDa, and only 2-3% of LREY and 6-12% of HREY are truly dissolved, while in the Råne River these fractions are about 3-4% and 6-9%. These results from 2017 for low river discharge will be compared to most recent data from 2019 for high river discharge.

[1] Pokrovsky et al. (2014) Ocean Sci. 10, 107-125.



Mon: 20
Topics: 4e) Archives of environmental changes throughout Earth history

Calcification, skeletal structure and composition of the cold-water coral Desmophyllum dianthus

Kristina K. Beck1,2, Grit Steinhoefel1, Jürgen Laudien1, Gernot Nehrke1, Marlene Wall3, Jan Fietzke3, Claudio Richter1,2, Gertraud M. Schmidt-Grieb1

1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany; 2University of Bremen, Bremen, Germany; 3GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany

In the naturally acidified Comau Fjord (Chile), high densities of the cosmopolitan cold-water coral Desmophyllum dianthus are found at or below aragonite saturation (Ωar ≤ 1). However, it is not known so far if seasonal changes in Ωar lead to seasonal differences in calcification rates and the corals’ ability to up-regulate the pH in the calcifying fluid (pHcf). Corals were sampled in Comau Fjord along both horizontal and vertical pH gradients (pHT = 7.6-7.9, Ωar = 0.76-1.45). The calcification rates (buoyant weighing technique) of D. dianthus were compared between austral summer 2016/2017 and winter 2017 and related to the respective physico-chemical conditions in the water column (T, Ωar). In order to determine the biological pHcf up-regulation of D. dianthus, the skeletal boron isotopic composition (δ11B) was measured in the upper part of the calyx between the septa, using a UV femtosecond laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS). Higher growth rates of D. dianthus were found in summer than in winter. Surprisingly, growth of D. dianthus was highest in near-bottom, undersaturated waters in both seasons (Ωar = 0.76 and 0.84) and cross-transplanted specimens from shallow to deep waters were able to acclimatise to Ωar < 1. Therefore, the present study shows that Ωar alone is a poor predictor of D. dianthus growth. Skeletal analyses show a complex relationship between δ11B and the structure of the coral skeletons. δ11B measurements are highly variable, which may be attributed to the high calcification rates in the upper part of the coral calyx. Therefore, high resolution analyses of the skeletal composition and micro-structure will be conducted along the entire longitudinal section of D. dianthus skeletons using Raman microscopy and scanning electron microscopy (SEM). In addition, δ11B will be measured in different skeletal parts and compared to skeletal structure analyses for a reliable reconstruction of seawater pH at high temporal resolution using skeletons of D. dianthus grown under laboratory and field conditions (Comau Fjord, Chile).



Mon: 21
Topics: 4e) Archives of environmental changes throughout Earth history

The relation between Δ'17O and bodymass for bioapatite

Dingsu Feng, Andreas Pack

Georg-August-Universität Göttingen, Abteilung Isotopengeologie, Geowissenschaftliches Zentrum, Goldschmidtstraße 1, 37077 Göttingen,Germany

The reconstruction of paleo-atmospheric CO2 levels by proxies is still one of the most important challenges of modern climate research. The Δ'17O of air O2 varies with atmospheric CO2 concentrations. Bao et al. (2008) presented an approach for reconstruction of the atmospheric CO2 levels on the basis of a 17O anomaly in sulfates. Pack et al. (2013) proposed that bioapatite of terrestrial mammals can also be used as a proxy for the Δ'17O of ambient air and hence atmospheric CO2 levels. Mammals breathe in O2 to metabolize carbohydrate, fat, and protein. The Δ'17O anomaly of air O2 is transferred to the reaction products CO2 and H2O. Both CO2 and H2O equilibrate with body water so that the anomaly is transferred from inhaled O2 to body water of mammals. Bioapatite crystallizes in isotopic equilibrium from body water. Because body water contains a fraction of anomalous O2 from the respiration of air O2, bioapatite should carry information on the isotope composition of air O2. The amount of oxygen from respired air O2 can be estimated using a mass balance model (Pack et al. 2013). This mass balance model, however, has large intrinsic uncertainties and must be compared to large data. For better interpretation, we achieve to obtain more data from modern animals.

We collected modern samples of bioapatite that crystallized at temperatures between 0℃ and 37°C. For the sample preparation, the modern samples were heated to 1000°C to remove the carbonate fraction of the bioapatite in the furnace. The triple oxygen isotope measurements of the phosphate fraction of the bioapatite were conducted by infrared laser fluorination using purified F2 in combination with gas chromatography isotope ratio monitoring gas mass spectrometry.

A new database of animals from desert to aquatic habitats will be systematically built up.

References

Bao et al. (2008). Nature 54: 349-392.

Pack et al. (2013) Geochimica et Cosmochimica Acta. 102, 306-317.



Mon: 22
Topics: 4e) Archives of environmental changes throughout Earth history

Palynofacies as an indicator for transgressive-regressive trends in offshore marine mudstones – a critical evaluation

Hauke Thöle1,2, Ulrich Heimhofer1, Andre Bornemann2, Jochen Erbacher2,3

1Leibniz Universität Hannover, Germany; 2Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany; 3Landesamt für Bergbau, Energie und Geologie (LBEG), Hannover, Germany

Stratigraphic distribution patterns of particulate organic matter (POM) within sediments have been widely used for facies recognition and paleoenvironmental interpretation as well as to decipher proximal to distal trends within fine-grained sediments. The Lower Cretaceous mudstone-dominated succession in the eastern Lower Saxony Basin (LSB) offers an excellent opportunity to critically evaluate palynofacies parameters which have been commonly used to identify transgressive-regressive (T-R) cycles in marine sediments. For the seemingly monotonous succession, a robust sequence stratigraphic framework has been established by integrating high-resolution elemental intensity data from XRF-core scanning with organic carbon isotope chemostratigraphy and biostratigraphic information from four drill cores. Stratigraphic trends in Si/Al ratios are interpreted to reflect grain size variations and enable identification of six T-R cycles during the Berriasian to Aptian interval in the LSB. The composition and distribution of the POM has been assessed by analysis of 220 strew mounts using transmitted-light microscopy. POM is dominated by opaque and translucent phytoclasts (ø = 49.3 %) with amorphous organic matter (ø = 13.2 %) being mostly of subordinate importance. Marine and terrestrial palynomorphs account for roughly similar fractions with 21.1 % and 16.3 %, respectively. Overall, the POM composition indicates deposition in a mud-dominated distal to proximal shelf setting. The ratio of opaque versus translucent phytoclasts (OP/TR ratio) shows a distinct long-term increase from the Berriasian onwards with maximum values during the Lower Hauterivian, followed by a subsequent decrease in OP/TR ratio. This trend broadly reflects the overall transgressive-regressive evolution of the succession interpreted from Si/Al changes. On the other hand, the ratio of terrestrial versus marine palynomorphs (T/M ratio), often applied as indicator of proximal to distal trends and distances from the coastline, shows no correlation with the T-R cycles inferred from XRF-core-scanning data. Interestingly, systematic long- and short-term trends visible in T/M ratio correspond to variations in the XRF-derived Ca/Ti stratigraphic trend, which is interpreted to reflect variations in carbonate content. This may indicate that the T/M ratio in the LSB is largely controlled by variations in marine palynomorph flux, probably related to productivity changes of the organic-walled microplankton. In summary, the comparison of the palynofacies parameters with the independently derived T-R cycle framework for the Early Cretaceous mudstone-dominated succession shows an overall good correspondence with the OP/TR ratio. In contrast, application of the T/M ratio must be used with caution since other factors (e.g. productivity) may exert a significant influence on this ratio.



Mon: 23
Topics: 4e) Archives of environmental changes throughout Earth history

Distribution patterns of some ʽrhenotypicʼ faunal elements related to a sea-level rise during the Emsian/Eifelian transition in the eastern Rhenish Massif (Sauerland and Bergisches Land).

Simon Felix Zoppe

Goethe-Universität, Institut für Geowissenschaften, Altenhöferallee 1, 60438 Frankfurt am Main, Germany

Distribution patterns of marine invertebrates were analysed with regard to a documented facies shift during the Lower/Middle Devonian (= Emsian/Eifelian) transition in the eastern Rhenish Massif (Sauerland and Bergisches Land). During this time interval, the southeastern Sauerland was part of a shelf/basin transition zone at the southern margin of Laurussia (Old Red Continent), which is characterized by this major shift from neritic (ʽrhenotypicʼ) to pelagic (ʽhercynotypicʼ) environments (see e.g. [1][2]). This facies shift was driven by a sea-level rise transgreded from southeast direction. So far, analysed taxa include the branching tabulate coral Coenites vermicularis (McCoy, 1850) and the spiriferid brachiopod Paraspirifer (Paraspirifer) cultrijugatus (Roemer, 1844) sensu stricto (including form a sensu Solle, 1971).

In the research area, the earliest known occurrences of Paraspirifer cultrijugatus are restricted to the uppermost Emsian (upper Kondel substage) of the southeastern Sauerland (e.g. [1]; own collections). In the northwestern Sauerland, Paraspirifer cultrijugatus persisted into the lowermost Eifelian [3]. The youngest known occurrence is from the lowermost Hobräck Formation in the Bergisches Land [4], and could be of special interest regarding to the extinction event of the ʽOCA faunaʼ (sensu Struve, 1982b[5] & add. Jansen, 2016[6]) in the lowermost Eifelian. The precise stratigraphic position of the extinction of this brachiopod assemblage was approximately determined just in parts of the research area (compare with [3]).

The tabulate coral Coenites vermicularis is well known from the lowermost Eifelian (upper Cultrijugatus Beds and Hobräck Formation) in the northwestern Sauerland [3][7][8]. Coenites vermicularis was quite abundant and an important ʽbafflerʼ in the first biostromal reef ecosystems of this area (e.g. "Meinerzhagener Korallenkalk")[3][8]. The oldest known occurrences of Coenites vermicularis are from siliciclastic strata of the Orthocrinus Formation (uppermost Emsian) in the southeastern Sauerland (e.g. [7]; own collections).

This preliminary overview suggests that both species show westward directed patterns of colonization across the eastern ʽRhenish shelfʼ (today's Sauerland and Bergisches Land), which were most likely caused by a sea-level rise during the Emsian/Eifelian transition. The resulting facies changes (e.g. in sediment flux, water energy or substrate composition) possibly limited the suitable bottom conditions for both benthic organisms in the southeastern Sauerland. However, in the northwestern Sauerland and Bergisches Land both taxa still persisted into the Lower Eifelian. Further work and comparisons with other marine invertebrates would be necessary to verify this trend.

References: [1] Langenstrassen, F. (1972) Göttinger Arb. Geol. Paläont., 12: 1-106. [2] Goldring, R. & Langenstrassen, F. (1979) Spec. Pap. Palaeont., 23: 81-97. [3] Avlar, H., & May, A. (1997) Coral Res. Bull., 5: 103-119. [4] Solle, G. (1971) Abh. hess. L.-Amt Bodenforsch., 59: 1-163. [5] Struve, W. (1982b) Cour. Forsch.-Inst. Senckenberg, 55:401-432. [6] Jansen, U. (2016) Spec. Pap., 423: 45-122. [7] May, A. (2003) Geol. Paläont. Westf., 60: 47-79. [8] Ernst, A., May, A., & Marks, S. (2012) Facies, 58:727-758.



Mon: 24
Topics: 5b) Volcanic geology

Alkaline volcanism on Patmos (Aegean Sea) – constraints from new radiogenic isotope data and 40Ar/39Ar dating

Katharina Boehm, Klaudia Kuiper, Pieter Vroon, Jan Wijbrans

Department of Earth Sciences, Faculty of Science, VU University Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam

The island of Patmos, in the eastern Aegean Sea, consists almost entirely of volcanic rocks of the late Miocene to Pliocene. Magmatism on Patmos was governed by subduction of the African below the Eurasian plate, back-arc extension, slab roll back and the final propagation of the Northern Anatolian Fault into the Aegean, accommodating westward extrusion of Anatolia.

The volcanic rocks of Patmos are special in terms of their alkalinity and variety in rock types. Fractionation, assimilation and mixing were the main processes, which lead to the production of suites of ne-Trachybasalts, hy-Trachyandesites, hy-Trachybasalts, trachytes, phonotlites and rhyolites. However, the volcanics of Patmos are not the only alkaline rocks in the Aegean- Western Anatolian realm. There are several late Miocene alkaline centers e.g. in Foca, Urla, Kula, Biga and Thrace. In the present study we verify whether or not these alkaline centers can be divided into isotopically distinct groups and how their age relations are with respect to each other. Further we strive to isotopically define the source evolution of the ne-trachybasalts and the timing between the different lava series on Patmos.

We present new radiogenic isotope data, including Pb, Nd, Hf, Sr, major and trace element data and additionally new precise 40Ar/39Ar age data on Patmos and Chillomodi. We sampled volcanic series, ranging from basaltic trachyandesites, to phonolites and rhyolites, with SiO2 from 52.7 -78.5 wt% and K2O from 1.9 -11.7 wt%. The 206Pb/204Pb ratios of 18.8-18.9 are likely to be elevated due to assimilation of arc crust and sediments. The 143Nd/144Nd values also fall in proximity to the Eastern Mediterranean Sediment (0.51239-0.51254). Trace element abundances are typical for alkaline arc lavas with enrichments in LREE and depletions in Nb, relative to N-MORB. Further characteristics are a distinct negative Ba anomaly, negative Eu anomaly, elevated Hf and Zr and for some sample depletion in Y with respect to N-MORB. Trace element ratios suggest a low subduction imprint in the phonolites and some of the younger volcanic rocks. Variations between the various volcanic lava series support models of AFM. Additionally, radiogenic isotopes place constraints on the source of the primitive alkaline magmas. Our work provides new insights into the characteristics and proportions of fluids derived from subducted oceanic crust, proportions of melts of subducted sediments, and the influx of depleted (or enriched) mantle.



Mon: 25
Topics: 5b) Volcanic geology

The Pliocene pyroclastic succession of Ani, Armenian-Turkish border: geochronology, geochemistry and paleomagnetic constraints

Hripsime Gevorgyan1,2, Uwe Kirscher3, Christoph Breitkreuz1, Khachatur Meliksetian2, Arsen Israyelyan2, Valerian Bachtadse4, Daniel Miggins5, Anthony Koppers5

1Institute of Geology, TU Bergakademie Freiberg, Bernhard-von-Cotta-Straße 2, 09599 Freiberg, Germany; 2Institute of Geological Sciences, National Academy of Sciences of Armenia, Marshal Baghramyan Avenue, Yerevan 0019, Armenia; 3Terrestrische Paleoklimatologie, Department of Geosciences, Eberhard Karls University Tuebingen, Sigwartstr. 10, 72076 Tuebingen, Germany; 4Department of Earth and Environmental Sciences, Geophysics, Munich University, Theresienstr. 41, 80333 Munich, Germany; 5College of Earth, Ocean, and Atmospheric Science, Oregon State University, Corvallis, OR, USA

Post-collisional Late Miocene to Holocene volcanic activity in Eastern Anatolia led to the formation of voluminous alkaline and high-K calc-alkaline volcanic rocks of highly variable composition ranging from basalt to rhyolite. Both the East Anatolian and the Armenian volcanoes record a large-scale regional magma generation in the lithospheric mantle usually associated with slab-breakoff processes. Nearly identical trace element patterns in these rocks provide strong evidence for a genetic relationship between the lavas and pyroclastic rocks from East Anatolia (Turkey) and those from the western border of the Aragats Volcanic Province (AVP) in Armenia.

The Ani pyroclastic succession crops out on the western periphery of Aragats volcano, near the Anipemza and Kharkov villages, situated on the Armenian-Turkish border, on both sides of Akhuryan river canyon. The Ani sequence commences with a c. 15 m thick package of Plinian pumice fall deposits that show conspicuous upward coarsening and enrichment of lithic fragments. It is covered by an 18 m thick yellow-colored pumice-rich (~ 40 vol%) dacitic to trachydacitic ignimbrite sheet. Based on i) the geochemical data obtained from selected pumice, bulk rock and fallout deposits, ii) the spatial distribution and thickness of the pyroclastic unit (~32 m), and iii) the geomagnetically reconstructed direction of the pyroclastic flows, the eruption center is presumably located in the nearby eastern periphery of the Kars Plateau in Turkey. According to available geological relationships of the Ani ignimbrites with dolerite basalts of the Akhuryan canyon, as well as new 40Ar/39Ar age determinations and magnetostratigraphy, the Ani ignimbrites are referred to the late Upper Pliocene or the Gauss normal polarity chron.



Mon: 26
Topics: 5h) Processes and timescales in the evolution of transcrustal magma systems

Geodynamic constraints on the initiation of mélange diapirs from subducting slabs

Nicolas Berlie1, Boris Kaus1, Horst R. Marschall2

1Johannes Gutenberg University Mainz, Germany; 2Goethe University, Frankfurt am Main, Germany

Subduction zones represent an important part of the general volcanic activity and magma production on our planet. Numerous geochemical analyses have been performed over time on those magmas and the results suggest a mixing between the crustal components of the subducting slab and the mantle. The mixing process likely takes place at the interface between the slab and the mantle wedge, where mélange rocks form comprising of crustal and mantle rocks and hydrous fluids extracted from the slab. This mélange layer would then evolve into diapirs and rise in the asthenosphere until it reaches melting conditions suitable for the creation of magmas. Here, we study the geodynamic feasibility of this process and the conditions that determine the ability of the mélange to peel off from the slab and to form diapirs as well as the size of those diapirs. We perform 2D finite element calculations focusing on two different setups to observe the initiation and later the evolution of the diapirs with time. Results confirm that this mechanism is feasible under a specific range of condition and we show how the lateral extents of those diapirs along the slab depends on the geometry of the slab, the rheological and density parameters of the mélange layer and the overlying mantle. We also investigate the P-T paths followed by the diapirs and the implications on their mineralogical compositions.



Mon: 27
Topics: 5h) Processes and timescales in the evolution of transcrustal magma systems

Times of magma ascent and residence reflected in Mg/Fe and Ni diffusion in olivine from arc lavas in Kamchatka

Tatiana Churikova1,2, Boris Gordeychik1,3, Gerhard Wörner1, Andreas Kronz1, Maria Pevzner4, Yaroslav Muravyev2, Alexander Belousov2, Oleg Dirksen2

1Geowissenschaftliches Zentrum Göttingen, Abteilung Geochemie, Georg-August-Universität Göttingen, Göttingen, Germany; 2Institute of Volcanology and Seismology FEB RAS, Petropavlovsk-Kamchatsky, Russia; 3Institute of Experimental Mineralogy RAS, Chernogolovka, Russia; 4Geological Institute RAS, Moscow, Russia

Time scales of residence and ascent for Kamchatka magmas are presented based on zoned olivines from basalts of distinct volcanic modes: maars, monogenic cones, dikes and stratovolcanoes.

The time scales were estimated by Ni-Mg/Fe diffusion modeling of zoning in olivine crystal cores and outer rims by quantitative geochemical profiles. Modeling is based on the analytical solution of diffusion equation to approximate measured geochemical profiles and estimates for P and T from Al-in-olivine thermometry and cpx-melt barometry.

Olivine crystals in basalts erupted from of maars preserved the most diverse types of compositional zonation – normal, inverse, and even oscillatory in Fo78 to Fo92 olivines. The size of olivine crystals in maar eruptions is small (<0.3 mm) compared to olivines from other eruptive regimes, which indicates short crystal growth times. Crystal residence times and time of magma ascent are estimated at 100-2000 and 1-10 days, respectively. Magmas erupted in maars thus move most rapidly to the surface.

In lavas erupted at monogenic cones, oscillatory zonation in olivine is absent, but normal and inverse zoning are found in all samples, with sharp gradients between the cores and outer parts of crystals. The size of the crystals in monogenic cones is larger than for maar lavas (<0.5 mm). The time of magma ascent varies from 10 to 60 days. Residence time, estimated for few crystals lasted up to 300 days.

The size of olivine crystals in dikes and stratovolcanoes are larger (0.8-1 mm), which indicates a relatively longer time of crystal growth in their feeding systems. The majority of crystals show normal zoning. Compositional gradients in Fo and Ni between the olivine cores and outer parts are smoother, indicating longer diffusion times. Also, olivine with reverse zoning and compositional gradients in their cores are rare in samples from stratovolcanoes. Diffusion therefore probably erased earlier zonation gradients. The diffusion times for dikes and stratovolcano lavas were estimated up to 200 and 1500 days, respectively.

The implication of these results is as follows: Maar eruptions are fed from rapidly ascending magmas that do not reside, cool and fractionate during ascent fast from their mantle reservoirs. Monogenetic cones are similarly sourced from magmas that ascended relatively fast. By contrast, lavas erupted in stratovolcanoes and those that ascended through their feeder dikes have longer residence times in crustal magma systems, where crystallization, mixing and magma processing occurs.

Research was supported by grants GSF Wo 362/51-1 and RFBR 16-55-12040.



Mon: 28
Topics: 5h) Processes and timescales in the evolution of transcrustal magma systems

Variations of Fo and Ni in the centres of olivine cores reflect processes of crystallization and diffusion

Boris Gordeychik1,2, Tatiana Churikova1,3, Alexander Simakin2,4, Thomas Shea5, Gerhard Wörner1

1Geowissenschaftliches Zentrum Göttingen, Abteilung Geochemie, Georg-August-Universität Göttingen, Göttingen, Germany; 2Institute of Experimental Mineralogy RAS, Chernogolovka, Russia; 3Institute of Volcanology and Seismology FEB RAS, Petropavlovsk-Kamchatsky, Russia; 4Institute of Earth Physics RAS, Moscow, Russia; 5Department of Geology and Geophysics, University of Hawai‘i, Honolulu, USA

Mg and Ni are both compatible elements in olivine. Fractional crystallization of olivine typically results in a concave up trend on a Fo-Ni diagram. "Ni-enriched" olivine phenocrysts that fall off and above the crystallization trend of are commonly observed in subduction and intraplate settings. To explain such “Ni-enriched” olivine crystals, we develop a set of theoretical and computational models to describe how primitive (high-Fo, high-Ni) olivine phenocrysts from a parent basalt re-equilibrate with an evolved (low-Fo, low-Ni) melt through diffusion. These models describe Fo and Ni decreasing in olivine cores during protracted diffusion for different crystal shapes and variable relative diffusivities for Ni (DNi) and Mg-Fe exchange (DFo). Such dependence is considered as a diffusion trend responsible for the formation of Ni-enriched olivine phenocrysts. Theoretical models show if the diffusivity of Ni is lower than the diffusivity of Fo, then affected by diffusion the olivine phenocrysts form a concave down trend that contrasts with the concave up crystallization trend. These models with different geometries allow showing the diffusion trend does not depend on the size of the crystal and weakly depends on its shape. In addition, it is shown that the anisotropy of the diffusion coefficient affects the diffusion trend in the same way as a change in the crystal shape and both features, anisotropy and shape, do not significantly change the concave down diffusion trend. Three-dimensional numerical diffusion models using a range of realistic olivine morphologies with anisotropy corroborate this conclusion. Thus, the curvature of the concave down diffusion trend is mainly determined by the ratio of the diffusion coefficients DNi/DFo. The initial and final points of the diffusion trend are determined by the compositional contrast between mafic and more evolved melts that have mixed to cause disequilibrium between olivine cores and surrounding melt. These endmember compositions may also vary in nature. We present several examples of measurements on olivine from arc basalts from Kamchatka, and several published olivine datasets from mafic magmas from non-subduction settings (lamproites and kimberlites) that are consistent with diffusion-controlled Fo-Ni behavior. In each case the ratio of the Ni and Fo diffusion coefficients is indicated to be <1. These examples show that crystallization and diffusion can be distinguished by concave up and concave down trends in Fo-Ni diagrams.

Research was supported by grants GSF Wo 362/51-1 and RFBR 16-55-12040.



Mon: 29
Topics: 5h) Processes and timescales in the evolution of transcrustal magma systems

Divergent compositional domains in the shallow plume mantle beneath the West Eifel volcanic field, W Germany

Andreas B. Kaufmann1, Stephen J. G. Galer2, Dieter F. Mertz1

1Institute for Geosciences, University of Mainz, Germany; 2Max Planck Institute for Chemistry Mainz, Germany

Low-SiO2 volcanic activity in the Pleistocene West Eifel volcanic field (WEVF) is related to a seismological low-velocity anomaly in the upper mantle (“Eifel Plume” [1]). In the WEVF, two geographical groups can be distinguished by their characteristic elemental and isotope compositions combined with their geochronological evolution [2]. Lava flows >480 ka exclusively occur in the NW, <80 ka flows extruded in the SE. However, there are two specific flows, from Sarresdorf and Emmelberg, that do not fit into this general time-space-composition pattern within the WEVF.

Lava flow Sarresdorf is located in the NW, i.e. within the >480 ka group, but is characterized by an 40Ar/39Ar plateau age of 32 ±13 ka (1σ), along with the highest Nb/Ta (22.7), Lu/Hf (0.07) and Sr concentration of 1810 μg g-1 (other flows average ca. 1000 μg g-1) as well as the lowest (Ti/Eu)N (0.56) among the West Eifel flows (n = 27) investigated. This specific composition is interpreted as resulting from the influence of carbonatitic melts, which is supported by elemental evidence from other volcanic fields [3, 4].

Lava flow Emmelberg has an 40Ar/39Ar plateau age of 49 ± 2 ka (1σ) and extruded at the geographical boundary between the <80 ka and >480 ka compositional groups. With respect to the <80 ka-old group, it has elevated (Zr/Sm)N of 1.07 and K2O/TiO2 of 0.95 as well as more radiogenic 208Pb/204Pb of ca. 39.45 at a given 206Pb/204Pb of 19.36-19.51 and more radiogenic Sr. This composition is consistent with the occurrence of zircon megacrysts in the Emmelberg lava originating from mantle melts which differentiated into syenite intrusions [5]. Since lavas of the >480 ka group to a large extent show higher (Zr/Sm)N (0.82-1.22) and K2O/TiO2 (0.81-1.25) compared to that of the Emmelberg lava, it appears that sub-surface syenite intrusions are common within the region comprising the >480 ka-old lavas, i.e. in the NW of the West Eifel.

Since the surface-projected seismological P-wave anomaly corresponds geographically to the <80 ka-lava region in the SE, but not to that of the >480 ka volcanism in the NW, the younger plume activity appears to lack syenitic products at depth.

[1] Ritter et al. (2001), Earth Planet. Sci. Lett. 186, 7-14; [2] Mertz et al. (2015), J. Geodyn. 88, 59-79; [3] Pfänder et al. (2012), Geochim. Cosmochim. Acta 77, 232-251; [4] Brandl et al. (2015), J. Petrol. 56, 1743-1774; [5] Schmitt et al. (2017), J. Petrol. 58, 1841-1870.



Mon: 30
Topics: 5h) Processes and timescales in the evolution of transcrustal magma systems

U/Th disequilibrium dating of Late Quaternary perovskite

Yi Sun, Axel Karl Schmitt

Heidelberg University, Germany

Perovskite occurs as an accessory phase in late Quaternary alkali basalts of the West Eifel Volcanic Field (WEVF). It is often present as euhedral to skeletal-arborescent crystals in clefts or vesicles of lava flows, which indicates late-stage formation during or briefly after eruptive emplacement. Selected perovskite crystals from four different volcanoes (Rother Kopf, Grauley, Loehley, Emmelberg) were dated by a novel method of 238U/230Th perovskite geochronology using secondary ion mass spectrometry (SIMS). In addition, trace element abundances in perovskite were determined with SIMS to provide insight into the conditions and processes related to its formation.

Perovskite crystals from the WEVF contain Fe, Nb, LREE and in some cases Sr as minor elements in concentrations up to several wt%. Traces of Ta, U and Th are present in concentrations of a few 1000 μg g-1. Comparatively high Pb with common isotopic composition renders U-Pb perovskite dating of such young crystals impossible. Perovskite crystals from the older activity period of the WEVF (Rother Kopf, Grauley, Loehley) are enriched in Th relative to U, with observed (238U)/(232Th) activity ratios ranging from 0.114 to 0.824. By contrast, Emmelberg perovskite from the younger WEVF eruptive pulse are generally highly enriched in U with (238U)/(232Th) activity ratios up to 14. Perovskite from Rother Kopf, Grauley and Loehley have reached secular equilibrium, consistent with known or inferred eruption ages >480 ka from the literature. Emmelberg perovskite analyses, by contrast, plot along a well-defined isochron in the (230Th)/(232Th) versus (238U)/(232Th) diagram yielding an isochron age of 48.4 ± 2.4 ka (2σ). The 238U/230Th perovskite age for Emmelberg volcano closely agrees with published 40Ar/39Ar leucite ages averaging 49 ± 4 ka, albeit with smaller uncertainties. This underscores that 238U/232Th perovskite ages represent eruption ages due to their rapid crystallization in a late-magmatic, pneumatolytic stage shortly after lava flow formation. The results demonstrate the potential of perovskite for 238U/230Th disequilibrium geochronology for late Pleistocene samples where analytical precision at the millennial timescale can be achieved. Perovskite present in deposits from late Pleistocene-Holocene alkaline volcanism such as in Southern Italy or the East African Rift are possible targets for this method.



Mon: 31
Topics: 6b) Reaction and deformation

The role of chemically induced stresses in the mechanisms of element exchange between minerals – an experimental study based on pyroxenes

Jennifer Primocerio1, Sumit Chakraborty1, Katharina Marquardt2, Thomas Fockenberg1

1Ruhr-Universität Bochum, Germany; 2Imperial College London, UK

The mechanism by which element transfer processes occur in minerals remains unclear. Recent technological developments now make it possible to observe the different steps by which compositional changes occur in mineral pairs. Pyroxenes, very common terrestrial and extraterrestrial minerals, have been studied for decades now. So, in this study we built on the available information to analyze the element transfer processes using orthopyroxene-clinopyroxene pairs.

For this purpose, we synthesized crystals of ortho- and clinopyroxene of different Fe/Mg ratios from appropriate oxide mixes. The synthesis experiments were carried out at high temperatures (1000 – 1250 °C) at atmospheric pressures as well as at high pressures (15 kbar) in a piston cylinder apparatus. We performed three kinds of element exchange experiments: (A) polished sample cubes of natural crystals with deposited thin films (produced using pulsed laser deposition, PLD) at 1 bar and 1000-1200 °C in a gas mixing furnace. (B) Anneals of powder mixes of pre-synthesized pyroxenes at 1 bar, 1000-1200 °C in a gas-mixing furnace. (C) Anneals of the same mixes in the piston cylinder apparatus at 15 kbar and 900-1200 °C. The starting materials and run products were further characterized using BSE (back-scattered electron) imaging, chemical analysis in the electron microprobe at different analytical conditions, and structural and chemical characterization in the TEM (transmission electron microscopy) of lamellae produced by focused ion beam (FIB) thinning.

It is generally assumed that the compositions at the interface of two grains attain equilibrium instantaneously, whereas the rest of the crystals equilibrate by diffusion. We observed that the samples equilibrate by a different, multi-step process.

Experiments of type (A) demonstrate that recrystallization and element exchange (e.g. the incorporation of the larger Ca ion in the lattice) of two pyroxenes in a direct interface cause distortion of the lattice and produce mismatch dislocations which can then act as fast diffusion pathways. In experiments of type (B) and (C) compositions equilibrate step wise along two different paths, depending on whether the T-X combination is above or below the pyroxene miscibility gap. Grains recording different stages of compositional evolution may be seen in a single sample. Newly recrystallized grains have a low density of dislocations, compared to grains with the starting composition which have a high density of defects of different kinds.

Thus, the process of equilibration involves both, recrystallization and diffusion in tandem, rather than exclusively the one or the other.



Mon: 33
Topics: 6b) Reaction and deformation

Episodic deformation and metamorphic reactions at decreasing distances to the tip of a seismic active fault zone – the record of mylonites from the DAV, Eastern Alps

Claudia A. Trepmann1, Felix Hentschel1, Emilie Janots2

1Ludwig-Maximilians University Munich, Germany; 2University Grenoble, ISTerre, France

Microfabrics in quartz-rich mylonites from the Deferregen-Antholz-Vals (DAV) shear zone in the Eastern Alps that underwent Alpine episodic stages of deformation and metamorphism (450-300°C) are presented. During an initial stage, dislocation glide of quartz was the dominant deformation mechanism, as indicated by quartz grains with long axes of several hundreds of µm and width of a few tens of µm that are preferentially oriented with the c-axis at low angle to the y-axis of the finite strain ellipsoid. Monazite grains are surrounded by apatite, allanite and epidote forming elongate corona microstructures that are aligned in the foliation and deflecting it. These corona microstructures indicate coeval metamorphic breakdown reactions of monazite. At a later stage of greenschist facies conditions at which biotite was still stable, shear bands formed associated with fracturing of all rock-forming minerals. Distributed fracturing at these conditions indicates high differential stresses and strain rates. Mainly quartz and minor biotite precipitated from the pore fluid along the shear band boundaries and in the interspace between fragments, indicating that fluid availability increased transiently, probably related to increased connectivity of the pore space due to fracturing. Quartz grains within shear bands show c-axis being preferentially perpendicular to the shear band boundary. At a final stage but at still metamorphic conditions, cataclasis of the mylonites occurred locally, as indicated by breccias with cm-scaled rounded mylonitic components in a mica-rich matrix. The fault rocks from the DAV record systematically changing rheological behaviour during various stages of deformation at greenschist facies conditions from dislocation glide-controlled deformation of quartz to cataclasis. The time-dependent rheological behaviour is suggested to be dominantly governed by the changing stress and strain rate conditions, as opposed to changing temperature conditions. We interpret the record to represent episodic deformation and metamorphic reactions at decreasing distances to the tip of a seismic active fault zone.



Mon: 34
Topics: 6c) Fluid-rock interaction: from mechanisms to rates – from atoms to plates

Chemical controls of the aqueous environment on mineral growth and dissolution

Helen E King

Utrecht University, Netherlands, The

Interfacial processes of mineral growth and dissolution are dictated by the local chemical environment. Even the distance from equilibrium, called the solution saturation, is dependent on the aqueous environment. If we look at organic molecules that do not interact directly with dissolved ions we can see that solubility changes with ionic strength [1]. This is known as salting out and is caused by the change in the network and hydration properties of water molecules, altering enthalpy and entropy contributions within the solution. When dissolved ions can interact with each other, as is common for mineral constituents, the story becomes more complicated. In this case, ion-pair formation can alter the saturation of the aqueous solution with respect to the mineral [2]. Furthermore, ions in the solution may also interact directly with the mineral surface [3], enhancing or inhibiting the addition or removal of ions and molecules to/from the surface. In this presentation I will review our knowledge of how aqueous solutions affect the growth and dissolution of carbonate minerals, which have been studied in detail at the interfacial level. Through this I will show that one of our major challenges to predict and understand fluid-rock interaction is modelling and characterizing the aqueous environment and its transitory nature.

[1] Whitehouse, B. G. The effects of temperature and salinity on the aqueous solubility of polynuclear aromatic hydrocarbons. Mar. Chem. 1984, 14, 319−332.

[2] King, H. E.; Satoh, H.; Tsukamoto, K.; Putnis, A. Nanoscale observations of magnesite growth in chloride-and sulfate-richsolutions. Environ. Sci. Technol. 2013, 47, 8684−8691.

[3] King, H. E.; Putnis, C. V. Direct observations of the influence of solution composition on magnesite dissolution. Geochim. Cosmochim. Acta 2013, 109, 113−126.



Mon: 35
Topics: 6c) Fluid-rock interaction: from mechanisms to rates – from atoms to plates

Tectonometamorphic and hydraulic processes along a fossil subduction plate interface in the northern Mirdita Ophiolites (Bajram Curri, Albania)

Madeline Richter1, Georg Löwe1, Kujtim Onuzi2, Kamil Ustaszewski1

1University Jena, Germany; 2Polytechnic University of Tirana, Institute of GeoSciences, Tiranë, Albania

The obduction of ophiolites onto passive margins is preceded by intraoceanic subduction. During incipient subduction, metamorphic soles with HT-assemblages form along the plate interface by overthrusting fluid-rich lower-plate material with hot, dry ultramafics of the upper plate. As lower plate material undergoes prograde metamorphism and dewatering, fluids are transferred along the plate interface and into the upper plate, assisting serpentinisation of upper plate mantle. To better understand interrelated tectonometamorphic and hydraulic processes associated with incipient intraoceanic subduction, we mapped ~35 km2 along the northern Mirdita Ophiolite near Bajram Curri, Albania. The Mirdita massif forms part of the Western Vardar Ophiolite Unit, cropping out along the entire length of the Balkan Peninsula. Oceanic lithosphere formed in the Triassic to Jurassic and was obducted onto the Adriatic passive margin by Late Jurassic. Lower plate material was progressively incorporated into a several km thick tectonic mélange at the base of the obducting ophiolite. Within the tectonic mélange, we distinguished several isoclinally folded units with mostly NE-plunging fold axes. Successions of sub-greenschist-facies turbiditic slates, arenites and olistoliths dominate structurally lower parts. Strata are coherent and exhibit a scaly or block-in matrix fabric, typical of broken formations. Structurally higher parts of the mélange contain intercalations of quartz-sericite schist, calc-schist, meta-chert, chlorite schist and Tlc-bearing serpentinite, indicating greenschist- to amphibolite-facies conditions. Structurally highest parts of the mélange consist of amphibolite and Grt-bearing paragneis. We hence observe an inverted metamorphic field gradient, typical of metamorphic soles worldwide. The base of coherent upper plate ultramafics, forming the actual plate interface, dips SE and truncates the folded, underlying tectonic mélange. Harzburgites show protomylonitic fabrics defined by finegrained matrix Ol and porphyroclasts of Opx. Arrays of abundant, systematically oriented, mm- to cm-thick veins crosscut basal harzburgites. Thin sections show three Srp vein generations in harzburgites. The first generation produces mesh-textures around Ol. Second generation veins are largest with up to 1.5 mm width consisting of fibrous Srp and opaque phases. They partly follow the metamorphic foliation formed by polymineralic layers of Ol+Opx. Third generation of yellow Srp dissects all other vein types. Bastitisation of Opx evolves at higher degrees of serpentinisation. Vein density substantially decreases upsection. There, massive harzburgites include Cr-Spl-rich dunite lenses. Our observations hence suggest that serpentinisation of peridotites by hydraulic fracturing is strongly localized along and immediately above the subduction interface and that this process is linked to dewatering of subducting material, which itself undergoes prograde metamorphism.



Mon: 36
Topics: 6c) Fluid-rock interaction: from mechanisms to rates – from atoms to plates

Sulfide mineralogy as a tracer for fluid-rock interaction in serpentinites

Esther Martin Schwarzenbach1, Roxana Rohne1, Oliver Plümper2

1Freie Universität Berlin, Germany; 2Utrecht University, Utrecht, The Nederlands

Fluid-rock interaction in ultramafic rocks leads to highly reducing conditions due the oxidation of ferrous iron in primary mineral phases. In both oceanic and continental sites of peridotite alteration (serpentinization) this results in fluids highly enriched in H2 and/or CH4 gas. In this regard, serpentinization systems are some of the most reducing environments found on Earth allowing for the stabilization of native metals and metal alloys and thus affecting the petrophysical properties of the oceanic lithosphere. At the Chimaera hydrothermal field in Turkey highly CH4-enriched fluids issue from an ultramafic basement that is undergoing serpentinization by circulation of meteoric water, though partial serpentinization already took place during mantle exposure along an oceanic spreading center. Here, we study the sulfur geochemistry and mineralogy of highly serpentinized peridotites to track sulfur sources, mobilization mechanisms of sulfur and the evolution of the redox conditions during hydrothermal alteration of these rocks.

Our results show that exposure of mantle rock to seawater along an oceanic spreading center in the Cretaceous resulted in the incorporation of seawater-derived sulfate as reflected in δ34Ssulfate values between 10.7 and 20.4‰. Simultaneously, water-rock interaction resulted in the modification of the primary mantle sulfide assemblages. In particular, the presence of awaruite and native Cu reflect highly reducing fluid conditions whereas hematite and magnetite record oxidizing conditions suggesting considerable changes in the redox conditions during fluid-rock interaction. These changes in redox conditions and the resulting disequilibrium conditions are also reflected in distinct decomposition features in sulfides with formation of e.g., native Cu as thin exsolutions. Furthermore, we infer that strong redox gradients on the micrometer scale are the result of late stage fluid infiltration – most likely during continental serpentinization and associated with highly reducing fluids – which overprinted earlier sulfide and metal mineral assemblages from oceanic serpentinization. These observations provide evidence that redox conditions strongly vary during the evolution of peridotite-hosted hydrothermal systems.



Mon: 37
Topics: 6c) Fluid-rock interaction: from mechanisms to rates – from atoms to plates

Solubility of forsterite, enstatite and magnesite in redox-buffered high-pressure COH fluids

Carla Tiraboschi1, Simone Tumiati2, Dimitri Sverjensky3, Thomas Pettke4, Peter Ulmer5, Stefano Poli2

1WWU Münster, Germany; 2University of Milan, Italy; 3Johns Hopkins University, USA; 4University of Bern, Switzerland; 5ETH Zürich, Switzerland

High-pressure fluids are able to mobilize and transport significant amounts of dissolved species resulting from fluid-rock interaction. Experimental constraints on the extent of mineral dissolution are therefore crucial to understand metasomatic processes closely related to the mass transport of elements by high-pressure fluids.

We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids synthesized employing a rocking piston cylinder apparatus at pressures from 1 to 2 GPa and temperatures from 700 to 1100 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H2O (ΔFMQ = -0.21 to -1.01), employing a double-capsule setting. Fluids, binary H2O–CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite + enstatite solubility in H2O–CO2 fluids is higher compared to pure water, both in terms of dissolved silica (mSiO2 = 1.24 mol/kgH2O vs. mSiO2 = 0.22 mol/kgH2O at P = 1 GPa, T = 800 °C) and magnesia (mMgO = 1.08 mol/kgH2O vs. mMgO = 0.28 mol/kgH2O) probably due to the formation of organic C–Mg–Si complexes.

Our experimental results show that at low temperature conditions a graphite saturated COH fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal. On the other hand, at high temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to carbon-free aqueous fluids. Therefore, in the mantle wedge, the amount of fluid required to metasomatize the surrounding peridotite decreases in the presence of carbon with increasing temperatures, leading to the formation of orthopyroxene-rich levels. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to shallowest level of the upper mantle.



Mon: 38
Topics: 7a) Quaternary Geochronology

A constant slip rate for the western Qilian Shan frontal thrust during the last 200 ka consistent with GPS-derived and geological shortening rates

Ralf Hetzel1, Andrea Hampel2, Pia Gebbeken1, Qiang Xu3, Ryan D. Gold4

1Institut für Geologie und Paläontologie, WWU Münster, Germany; 2Institut für Geologie, Leibniz Universität Hannover, Germany; 3Institute of Tibetan Plateau Research, Beijing, China; 4Geologic Hazards Science Center, U.S. Geological Survey, Golden, Colorado, USA

Active thrust faulting at the front of the Qilian Shan accommodates the northeastward growth of the Tibetan Plateau, however, the lifespan of individual faults and their slip history on different timescales remain largely unknown. Here, we show that the main range-bounding thrust fault of the western Qilian Shan has accrued tectonic slip at an almost constant rate during the last ~200 ka, and possibly since fault initiation in the mid-Miocene. Our finding is based on 10Be exposure ages from a flight of five deformed fluvial terraces along the Hongshuiba river, which constrain the vertical slip rate of the Qilian Shan frontal thrust to be 1.2±0.1 m/ka during the last 200 ka. With a fault dip of 30±5° constrained by seismic reflection data, we obtain a horizontal shortening rate of 2.0±0.3 m/ka. This value is consistent with both the short-term shortening rate of 1.7±0.3 mm/a derived from GPS data and the long-term shortening rate of 2.1±0.4 m/ka, which is based on a balanced geological cross-section. The latter provides a total shortening estimate of 25±3 km since the thrust fault initiated 12±2 Ma ago. The agreement between the shortening rates on the range of timescales between 100 and 107 years suggests that the western Qilian Shan frontal thrust has slipped at a steady rate since its initiation and implies that this fault is the main structure responsible for the growth of the western Qilian Shan.



Mon: 39
Topics: 7a) Quaternary Geochronology

Spatial patterns of erosion and landscape evolution in a bivergent metamorphic core complex revealed by cosmogenic 10Be: The central Menderes Massif (Western Turkey)

Caroline Heineke1, Ralf Hetzel1, Nils-Peter Nilius2, Christoph Glotzbach3, Cüneyt Akal4, Marcus Christl5, Andrea Hampel2

1WWU Münster, Germany; 2Leibniz Universität Hannover, Germany; 3Universität Tübingen, Germany; 4Dokuz Eylül University Izmir, Turkey; 5ETH Zürich, Switzerland

In extensional provinces with low-angle normal faulting – such as the Aegean region – both tectonic processes and erosion induce landscape change, but their interaction during the evolution of topography and relief accompanying continental extension has rarely been addressed. Here we present local and catchment-wide 10Be erosion rates that document the spatial pattern of erosion in the central Menderes Massif, a metamorphic core complex consisting of two asymmetric mountain ranges (Bozdağ and Aydın) bound by detachment faults and active grabens. Catchment-wide erosion rates on the northern flank of the Bozdağ Range are rather low (40–110 mm/kyr), but reach values of >300 mm/kyr on the steep southern escarpment; a pattern that reflects both topography and bedrock lithology. In the Aydın Range, erosion rates are generally higher – with mean erosion rates of ~190 and ~260 mm/kyr on the northern and southern flank, respectively – and more variable along-strike. In both ranges, the erosion of ridge crests, which we determined using amalgamated bedrock clasts, proceeds at rates of 30–90 mm/kyr. The difference between local and catchment-wide erosion rates indicates that topographic relief increases in most parts of the massif in response to ongoing fault-related uplift and concomitant river incision. The analysis of river profiles, drainage divide position and mobility suggests that rock uplift is strongest in the eastern Bozdağ Range and declines along-strike. Our findings document that tectonic processes exert a significant control on landscape evolution during active continental extension and are reflected in both the topographic signature and the spatial pattern of erosion.



Mon: 40
Topics: 7a) Quaternary Geochronology

A global geomagnetic field reconstruction of the past 100 ka

Sanja Panovska1, Monika Korte1, Catherine Constable2

1GFZ German Research Centre for Geosciences Potsdam, Germany; 2University of California San Diego, Scripps Institution of Oceanography, USA

The geomagnetic core field varies on time scales from months, years, centuries, to millennia. These variations are best studied using empirical spherical harmonic global models of Earth's magnetic field. Ground-based geomagnetic observatories and satellite missions provide a detailed view of the short-term variations. Paleo- and archeomagnetic data can be used to model the long-term variations. However, global field reconstructions become increasingly challenging with age, not least due to to uncertainties in dating of the input data. We recently derived the first global geomagnetic field reconstruction spanning the past 100 kyr, named GGF100k. One characteristic of the long-term variations are geomagnetic excursions - events when field directions deviate strongly from an axial-dipole dominated field, associated with globally low field intensities. The Laschamp excursion, is the globally best documented event and happened 41 ka ago. Some other, probably only regionally manifested excursions, have been described in the 0-100 ka time interval. Here we discuss the potential and limitations of using GGF100k as a paleomagnetic dating tool. Global field reconstructions show that care should be taken when using geomagnetic excursions as stratigraphic markers, as the field direction signature might only be regional or offset in time in different regions. We also point out the importance of good independent chronologies for paleomagnetic sediment records and volcanic data to improve global paleomagnetic field reconstructions like GGF100k for their broad applications in studying the geomagnetic field evolution, for estimating the past geomagnetic shielding effect, and for dating purposes.



Mon: 41
Topics: 7a) Quaternary Geochronology

An engineering geomorphologic characterization of the Kaju River near Qasr-e-qand city

Mahdiyeh Sotoudeh1, Jafar Rahnamarad1, Amir Hamzeh Keykha2, Kazem Shabanigoraji1

1Department of Geology, Zahedan Branch, Islamic Azad University, Zahedan, Iran,; 2Department of Civil Engineering, Zahedan Branch, Islamic Azad University, Zahedan, Iran,

Kaju River is one of the main streams of the Bahukalat River in the southern province of Sistan and Baluchistan, in Iran. The river extends approximately 200 km from the mountains of Qasr-e-qand and flows southward to Oman Sea. In this paper, we investigate the morphology, the spatiotemporal evolution and the engineering geomorphological characterization of the Kaju River. The data we use to analyze the geomorphology stems from library studies, field visits, geospatial map surveys, and aerial imagery. In recent years, the route of this river has changed significantly due to environmental and human factors. Environmental factors include frequent destructive floods, and increasing and decreasing sediment yield, whereas human factors include building and bridge constructions and side erosions due to the drainage of agricultural wastewater and urban sewage. We used the oldest available images which were scale 1:40000 aerial photographs from 1955. Based on the data analyzed in this paper, we determined the river’s characteristics such as central angle, type, longitudinal profile, and radius of curvature to width ratio. We also estimated the trend of changes and parameters such as slope and bending components, leading to the conclusion that the Kaju river as an adult river. The general shape of the Kaju River follows the geological conditions of the area. The river, with its many irregular branches, is flowing in a plain area with high hillsides. Tectonic factors have caused multiple bends along the river. The river bed’s width and large sediment yield indicate that the river is mostly arterial. Towards the river’s end, expected the river bed’s hard lithology, its route has rotated more than 90 degrees. This seasonal river, with its unexpected destructive floods, has a very wide mainstream bed during its typical flow, but during high water moments, the floodplain goes underwater. Finally, we show that agricultural land developments in the riverside’s proximity along the river’s route and the lack of awareness about efficient and eco-conscious ploughing and agricultural waste disposal methods have led to significant environmental degradation and changes in river morphology.



Mon: 42
Topics: 7a) Quaternary Geochronology

Glacial evolution using 36Cl moraine dating in the Krnica Valley, Julian Alps, Slovenia

Ron Steven1, Silke Mechernich1,2, Ariane Binnie1, Manja Zebre3, Roberto R. Colucci4, Jerney Jez5, Petra Jamsek Rupnik5

1Institute of Geolegy and Mineralogy, University of Cologne, Germany; 2Federal Institute of Hydrology, Germany; 3Department of Geography and Earth Sciences, Aberysthwyth University, UK; 4Department of Earth System Sciences and Environmental Technology, ISMAR Trieste – CNR, Italy; 5Geological Survey of Slovenia, Ljubljana, Slovenia

The impact of past climate change in the eastern Alps is rather unknown in relation to other parts of the Alps and central Europe. To fill this gap, the reconstruction of the age and size of glaciers can provide a better understanding of the glacier fluctuations and climate variability in the Alps since the Last Glacial Maximum (LGM).

Here we focus on the Krnica Valley, which is a 9 km long valley in the Julian Alps (Slovenia), located in an area characterized by very high mean annual precipitation that locally exceeds 3300 mm water equivalent. The valley is orientated to the north and indicates at least four moraine stages. The stratigraphically youngest moraine, associated with the Little Ice Age cooling, occupies the cirque threshold at 1910 m a.s.l. (stage I moraine after Kozamernik et. al., 2017). Further down valley at 1830 m a.s.l. occurs the frontal moraine of stage II. Moraine stages III and IV are preserved as lateral moraines, the latter reaching down to 1100 m a.s.l. Stage III moraine is significantly less vegetated and higher in its average altitude with respect to stage IV. The equilibrium line altitudes (ELAs) for the glacial advances associated with moraine stages I, II and III were estimated at 1973 m, 1923 m and 1812 m, respectively (Kozamernik et al., 2017).

The bedrock and the blocks on the moraines are composed of upper Triassic limestone and dolostone, which is suitable for Chlorine-36 (36Cl) dating. At well-preserved and stable boulders of moraines II-IV, hand sized samples were taken, their orientation and topographic shielding was documented. While the sampled boulders of stage III and IV are still under preparation, first results of five boulders from stage II indicate agreeing 36Cl concentrations, which will be calculated to exposure ages as soon as all required chemical data is available.

Further field investigations, glacier-climate modelling and final age calculation of the sampled boulders are aimed to clarify the local glacier fluctuations along with regional paleoclimatic interpretation.



Mon: 43
Topics: 7a) Quaternary Geochronology

The evolution of low relief landscapes in the Eastern Alps constrained by a multi-system approach

Andreas Wölfler1, Christoph Glotzbach2, Andrea Hampel1, István Dunkl3

1Institute for Geology, Leibniz Universität Hannover, Callinstraße 30, 30167 Hannover, Germany; 2Department for Geology and Geodynamics, Universität Tübingen, Wilhelmstraße 56, 72074 Tübingen, Germany; 3Geoscience Center, Sedimentology and Environment Geology, Universität Göttingen, Goldschmidstraße 3, 37077 Göttingen, Germany

The Eastern Alps comprise several domains, which are characterized by distinct geomorphologic features. The western footwall of the Katschberg normal fault in the Eastern Alps display high and rugged topography and high relief that is the result of the exhumation processes since the Miocene. In contrast, smooth topography and distinctly gentler dipping slopes occur to the east of the Katschberg normal fault, which are interpretated as remnants of paleosurfaces. These relict surfaces are preserved at elevations between 1.800 and 2.500 m a.s.l. Although these low relief landscapes have since long been recognized, little is known about their age and temporal evolution. To unravel their temporal and geomorphological history we use new low-temperature thermochronological data as well as 10Be-derived denudation rates of river catchmens and exposure ages of glacially polished quartz veins. The new low-temperature thermochronological data display a zircon (U-Th)/He age of 77.8±7.8 Ma that is interpreted to reflect late Cretaceous cooling after Eo-Alpine metamorphism. Apatite fission track and (U-Th)/He ages are significant younger and range from 36.8 to 31.3 Ma. Time-temperature history modelling of the cooling ages suggests enhanced cooling in the Eocene followed by thermal stagnation. Thus, the rocks of the study area have been in upper crustal sections (2-3 km) since the Eocene-Oligocene boundary (roughly between ~40 and ~35 Ma). The enhanced cooling in the Eocene is probably related to an increasing relief due to shortening, folding and thrusting in the Eastern Alps triggered by the onset of collision between the European margin and the Adriatic microplate. Catchment-wide erosion rates derived from cosmogenic 10Be analysis range from 98±9 to 180±20 mm/kyr. Under the assumption that rock exhumation occurred solely by erosion, the long-term average erosion rate derived from the thermochronological data range between ~50-90 mm/kyr. These long-term rates are remarkably similar to the 10Be-derived catchment-wide erosion rates, despite the different timescales over which the two methods integrate. Together, these data suggest that erosion rates did not change significantly over the last ~40 Ma. Four 10Be exposure ages from glacially polished quartz veins cluster between 14.5±1.4 and 16.8±1.6 ka. We interpret these ages as the record of the melting of glaciers in the study area shortly after the Oldest Dryas stadial.



Mon: 44
Topics: 7a) Quaternary Geochronology

Quantifying river incision into low-relief surfaces using local and catchment-wide 10Be denudation rates

Reinhard Wolff1, Ralf Hetzel1, Marcus Strobl2

1Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149 Münster, Germany; 2Steinbuch Centre for Computing, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany

Relief generation in non-glaciated regions is largely controlled by river incision into bedrock but datable fluvial terraces that allow quantifying incision rates are not always present (e.g. Ahnert, 1970; Whipple et al., 1999; Burbank and Anderson, 2012). Here we suggest a new method to determine river incision rates in regions where low-relief surfaces are dissected by streams. The approach consists of three steps and requires the 10Be concentrations of a stream sediment sample and a regolith sample from the low-relief surface. In the first step, the spatial distribution of 10Be surface concentrations in the given catchment is modelled by assuming that denudation rates are controlled by the local hillslope angles. The slope-denudation rate relation for this catchment is then quantified by adjusting the relation between slope angle and denudation rate until the average 10Be concentration in the model is equal to the one measured in the stream sediment sample. In the second step, curved swath profiles are used to measure hillslope angles adjacent to the main river channel. Thirdly, the mean slope angle derived from these swath profiles and the slope-denudation relation are used to quantify the river incision rate (assuming that the incision rate equals the denudation rate on adjacent hillslopes). We apply our approach to two study areas in southern Tibet and central Europe (Black Forest). In both regions, local 10Be denudation rates on flat parts of the incised low-relief surface are lower than catchment-wide denudation rates. As the latter integrate across the entire landscape, river incision rates must exceed these spatially averaged denudation rates. Our approach yields river incision rates between ~15 and ~30 m/Ma for the Tibetan study area and incision rates of ~70 to ~100 m/Ma in the Black Forest (Wolff et al., 2018). Taking the lowering of the low-relief surfaces into account suggests that relief in the two study areas increases at rates of 10-20 and 40-70 m/Ma, respectively.

References

Ahnert F. 1970. Functional relationships between denudation, relief, and uplift in large, mid-latitude drainage basins. American Journal of Science 268: 243–263.

Burbank DW, Anderson RS. 2012. Tectonic Geomorphology, Second Edition. Wiley-Blackwell Chichester, West Sussex. 472 pp.

Whipple KX, Kirby E, Brocklehurst SH. 1999. Geomorphic limits to climate-induced increases in topographic relief. Nature 401: 39–43.

Wolff R, Hetzel R, Strobl M. 2018. Quantifying river incision into low-relief surfaces using local and catchment-wide 10Be denudation rates. Earth Surface Processes and Landforms 43: 2327–2341.



Mon: 45
Topics: 7d) The stable isotope toolbox in sedimentary systems

Biological and lithological controls on Mg isotope fractionation in a forested watershed (the Black Forest, Germany)

Di Cai1, David Uhlig2, Michael J. Henehan1, Daniel A. Frick1, Friedhelm von Blanckenburg1

1GFZ German Research Centre for Geosciences; Section 3.3 Earth Surface Geochemistry; Telegrafenberg, D-14473 Potsdam, Germany; 2Institute of Bio- and Geosciences (IBG-3) Agrosphere, Forschungszentrum Jülich, Wilhelm Johnen Str., 52425 Jülich, Germany

We investigated variations in the stable isotope composition of magnesium (Mg) at a long-term experimental field site (Conventwald) from the Black Forest, Germany. From a 20 m drill core through the regolith, we analysed unweathered paragneiss bedrock, saprolite and soil, considering bulk geochemistry and the chemistry of differentiated clay-sized and exchangeable fractions. Additionally, plant tissues and time-series of groundwater, interflow and stream water were analysed. We investigated Mg isotope fractionation at different timescales: the geological timescale (how rock is converted into soil), the ecological timescale (how plants recycle nutritive elements) and the hydrological timescale (how biotic and abiotic processes affect water chemistry).

We observed the 26Mg/24Mg ratio in both bulk regolith and the clay-sized fraction (δ26Mg = +0.01 to +0.13‰) to be isotopically heavier than bedrock (∆δ26Mgregolith‑bedrock = 0.19‰). In situ analyses of bedrock minerals by femtosecond laser ablation revealed that of the two main Mg‑containing minerals, chlorite is isotopically 0.2‰ heavier than amphibole. Therefore, we propose that preferential dissolution of amphibole leads to enrichment of Mg with high δ26Mg in regolith. This is supported by mineralogical observations that amphibole is strongly depleted in the regolith.

Within the ecosystem, different plant species and compartments of plants show a larger range of isotopic compositions. Roots of both beech and spruce are isotopically similar at ‑0.18‰, while their foliage are around ‑0.35‰ (beech) and ‑0.74‰ (spruce), indicating fractionation during translocation within plants. Exchangeable Mg of soil, which should be the nutritive source for plants, has δ26Mg of ‑0.72 to ‑0.41‰ consistent with preferential uptake of isotopically heavy Mg by plants.

Hydrologically speaking, stream water shows little δ26Mg variability throughout a hydrological year. It has isotopically lighter Mg than bedrock (δ26Mgwater = ‑0.58 to ‑0.72 ‰) and is isotopically similar to the exchangeable fraction. Since it appears secondary mineral formation plays little role in regulating Mg isotope fractionation, the isotopic composition of stream water is likely controlled by biological processes. We hypothesize that release of light Mg isotopes from leaf litter decomposition, and uptake of heavy Mg isotopes by plants, set the composition of exchangeable Mg, which in turn buffers the composition of Mg in stream water.

Why plants, the exchangeable fraction, and stream water are all isotopically lighter than bedrock, and where the correspondingly heavy Mg isotopes are sequestered, remains enigmatic. Nevertheless, our study demonstrates that Mg isotopes reflect geological and ecological processes in forested watersheds.



Mon: 46
Topics: 7d) The stable isotope toolbox in sedimentary systems

Reconstruction of multimillenial changes in Eastern Tropical Pacific oxygen-minimum zones

Sümeyya Eroglu1, Renato Salvatteci2, Florian Scholz1, Christopher Siebert1, Ralph Schneider2, Martin Frank1

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany; 2Institute of Geosciences, University of Kiel, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany

The spatial extent and intensity of oxygen minimum zones (OMZ) in the Eastern Tropical North and South Pacific are controlled by ventilation, atmospheric dynamics, and biological productivity. Here, we present data of redox-sensitive trace metals (e.g. molybdenum, vanadium, uranium) of sediments and paleorecords from the Gulf of California OMZ, the center of the Peruvian shelf OMZ and its southern margin. The bottom waters of all these sites are presently anoxic, yet differ in water depth, primary productivity and particle rain in the water column. These different depositional conditions affect the metal influx, e.g. the mode of Mo supply and its isotopic composition (reported as δ98Mo).

The paleorecords cover almost the complete Holocene (~10,000 years), which was characterized by warm climate but interrupted by large multidecadal to millennial changes in ocean circulation, upwelling intensity and productivity that likely affected the spatial extent and intensity of the OMZs along the Eastern Tropical North and Pacific. By choosing different core locations along the OMZs we aim to interpret differences in elemental behavior of redox sensitive trace metals in terms of dynamic changes in the depositional conditions linked to climatic variations. The record from the Gulf of California shows low metal concentrations and no significant variations over time (Mo: 4-9 µg/g, V: 58-107 µg/g, U: 4-8 µg/g). The Peruvian records, in contrast, show overall higher concentrations and a larger variability, which are interpreted to reflect changes in the dynamics of the OMZ (“center” Mo: 19-98 µg/g, V: 61-307 µg/g, U: 5-24 µg/g; “margin” Mo: 3-36 µg/g, V: 98-280 µg/g, U: 2-16 µg/g). The δ98Mo signatures of the Gulf of California record are relatively uniform at +1.76 ± 0.15 ‰ (2SD) and close to isotopically heavy seawater. In this given environment, we interpret these results to indicate diffusive Mo supply to the sediment. In contrast, the Peruvian OMZ “center” record shows overall lighter Mo isotope compositions and larger variability at +1.46 ± 0.27 ‰ (2SD), which indicates supply of isotopically light Mo via particles [1]. These observations allow us to interpret Mo isotope variations in paleorecords regarding changes in the depositional conditions of permanent anoxic settings, e.g. upwelling intensity, ocean ventilation, and Fe cycling at the sediment-water interface along the shelf. We discuss the implications of these variations for the reconstruction of the paleoceanographic conditions at the Eastern Tropical North and South Pacific during the Holocene.

[1] Scholz et al. (2017) GCA 213, 400-417



Mon: 47
Topics: 7d) The stable isotope toolbox in sedimentary systems

Boron isotopes by femtosecond LA-ICP-MS with application to pH reconstruction in biogenic carbonates

Grit Steinhoefel, Kristina Beck, Albert Benthien, Klaus-Uwe Richter, Gertraud M. Schmidt-Grieb, Jelle Bijma

AWI Bremerhaven, Germany

In this study, we explore the capability of our customized UV femtosecond laser ablation system coupled to a Nu Plasma II MC-ICP-MS to determine B isotope composition by investigating standard materials of various matrices and foraminifera and coral samples. Boron isotope ratios were determined on ion counters using NIST SRM 610 as reference material. Multiple analysis of silicate and carbonate standard materials including NIST SRM 612, the MPI-DING series (komatiite to rhyolite glasses), IAEA-B-8 (clay) and JCp-1 (coral) reveal average d11B values, which agree well with published data. The reproducibility is better than 0.8‰ (2 SD). Investigations of the benthic foraminifera species (C. wuellerstorfi) from the ODP core 1092 show little inter- and intra-shell variability in d11B. Average d11B values reveal small variations around 14‰ at the time of cooling of Antarctica ~14 Myr ago, which indicate a change in deep water pH of ca. 0.1 pH units. Furthermore, we studied recent cold-water corals (D. dianthus) from the Comau Fjord (Chile), a field site showing spatial and seasonal variation in seawater pH (7.59 to 7.86). d11B values ranges between 23.5 and 27.0‰, which is controlled by ambient seawater pH but likely also by nutrient availability and precipitation rates. Our results demonstrate that fs-LA-ICP-MS provides a unique in situ technique to determine B isotope ratios at high spatial resolution for pH reconstruction.



Mon: 48
Topics: 7d) The stable isotope toolbox in sedimentary systems

Sediments of the supposed Ries impact ejecta-dammed "Rezat-Altmühl-Lake" (Miocene, Southern Germany)

Lingqi Zeng1, Dag Ruge1, Günther Berger2, Karin Heck3, Stefan Hölzl3, Andreas Reimer1, Dietmar Jung4, Gernot Arp1

1Geoscience Center, Universität Göttingen, Germany; 2Sudetenstraße 6, Pleinfeld, Germany; 3RiesKraterMuseum, Nördlingen, Germany; 4Geological Survey, Bavarian Environment Agency, Hof/Saale, Germany

Lacustrine and fluvial sediments are sensitive for climatic and other past environmental changes. The sediments of the Miocene Rezat-Altmühl-Formation have been previously considered as deposits of a lake dammed by Ries impact ejecta: a succession from redbrown clay to whitegrey marls and limestones. At first glance, they reflect increasing humid climatic conditions within the Miocene. However, recent biostratigraphic dating suggests a pre-impact age for the Rezat-Altmühl-Formation, thereby questioning the model of an ejecta-dammed lake.

In the investigated Pleinfeld drill core of the Rezat-Altmühl-Formation, the succession is characterized by floodplain fines, with paleosols and intercalated thin fluvial sandstone beds; to the top, the succession changes to carbonate-rich palustrine marls and limestones. No pebbles from the Ries ejecta material have been detected, only local clasts of the Mesozoic Keuper, Schwarzjura, and Braunjura Group, in addition to rare lydites. Likewise, fossils of the formation are dominated by terrestrial gastropods and only rare aquatic organisms (charophytes). Stable carbon and oxygen isotope results also do not favour a lacustrine origin. Samples from the entire drill section have a low, invariant δ18O and a highly variable δ13C, which reflects a short water residence time and a variable degree of pedogenesis, respectively. Carbonate 87Sr/86Sr ratios of entire drill section show a nearly unidirectional increasing trend, indicating a change of source of solutes from Triassic Keuper to Jurassic Schwarzjura-Braunjura rocks.

Our results suggest that the Rezat-Altmühl-Formation formed by a meandering, low-gradient river system with a narrow stream bed and dominant floodplains, rather than by the reportedly ejecta-dammed lake. The increasing trend of carbonate content in the succession reflects base-level changes from Upper Triassic Keuper to Lower/Middle Jurassic bedrocks, most likely related to an epirogenetic base-level change. This study invokes that similar successions changing from redbrown paleosol to carbonate may be unrelated to climate change but could reflect base-level and provenance controls.



Mon: 49
Topics: 8b) Deep subsurface groundwater systems

Krypton-81 feasibility study on deep thermal groundwaters in the karstified Upper Jurassic limestone of the Molasse basin (Germany-Austria)

Michael Heidinger1, Peter Mueller2, Jake Zappala2, Roland Purtschert3, Florian Eichinger1, Gunther Wirsing4, Tobias Geyer4, Thomas Fritzer5, Doris Groß6

1Hydroisotop GmbH, D; 2Physics Division, Argonne National Laboratory, USA; 3Physics Institute, University Bern, CH; 4State Authority for Geology, Mineral Resources and Mining Baden-Württemberg, D; 5State Authority for Environment Bayern, D; 6Department of Applied Geological Sciences and Geophysics Montanuniversity Leoben, A

The karstified Upper Jurassic limestone buried deep under tertiary sediments in the Molasse basin of south Germany and Austria is of special interest for its outstanding geothermal groundwater reservoir (up to 140 °C). Exploitation started in the 1930’s (mineralwaters, therapeutic baths) and developed to the actual status of more than 80 active wells (more than 30 geothermal wells/duplets for heating and green power production). Comprehensive studies (hydrogeology, hydrochemistry, stable and radioactive isotopes, gas and rare gas composition etc.) were done on local and regional scale. But little is known about the recharge and flow mechanism of the low mineralised Na-HCO3-Cl type thermal waters with glacial melt water characteristics predominant in the central basin close to the Alps. Especially radioisotope dating information (14C-DIC, He-isotopes, etc.) lacked to answer the open transregional/transnational topics, due to the complex evolution (ion exchange, isotope exchange, gas flux, etc.) of the deep thermal groundwater system.

Because of the achievement in the ATTA-technique for 81Kr-dating a feasibility study was proposed to regional/national water authorities and private geothermal plants. The results gained in 2017/18 reveal groundwater recharge during the last glacial period (Würm/Weichsel for central Europe) for the western and central part of the Molasse basin and seem to fit very well to the subglacial recharge hypotheses. For the mayor part of the karstified Upper Jurassic limestone in Molasse basin a transient groundwater flow system with very high turnover times during glacial periods is therefore plausible. In the eastern part of the Molasse basin the results show up a much slower flow system with less influence from alpine induced recharge during the latest glacial periods.



Mon: 50
Topics: 8b) Deep subsurface groundwater systems

Geothermal potential and thermal energy storage of Buntsandstein and Keuper aquifers in NE Bavaria

Cindy Kunkel1, Thorsten Agemar1, Ingrid Stober2

1Leibniz Institute for Applied Geophysics (LIAG), Stilleweg 2, 30655 Hannover; 2University Freiburg, Albertstr. 23b, 79104 Freiburg

This study investigates the hydraulic and thermic properties of siliciclastic aquifers in northern Bavaria with the aim to assess the geothermal potential of sandstone formations that could play a key role in Germany’s turn-around in heat production and supply (“Wärmewende”). Due to their wide spatial distribution, their depth and temperatures, especially the Buntsandstein und Keuper aquifers hold the highest potential for geothermal applications. Up to now, both aquifers are predominantly used for balneological purposes, but they can also be suitable for thermal energy storage (ATES).

Alluvial fan deposition under arid to semiarid conditions with periodical sheetfloods from the hinterland are dominant throughout the Buntsandstein. Especially the alluvial fans at the basin margin and the tectonically stressed regions are highly permeable, whereas the fine grained deposits in the basin center show rather unfavorable hydraulic properties. Deposition during the Keuper ranges from marine to brackish to fluvial environments under variable climate conditions resulting in vertical and lateral facies changes. Especially along the basin margin hydraulic properties are favorable due to an increase in the sand fraction.

Data from pumping tests and production data are interpreted to map the hydraulic conductivity of the Keuper and Buntsandstein aquifers for geothermal resources deeper than 100 m. Furthermore, temperature estimations and the depth levels of the two aquifers (Keuper 100 to 650 m, Buntsandstein 100 to 1,400 m) are incorporated. The results are visualized in form of spatial distribution maps of the hydraulic conductivity as well as temperature and will be integrated into the Geothermal Information System GeotIS (https://www.geotis.de).

The majority of the conductivity values of both aquifers are at depths of up to 300 m, occasionally up to 650 m. With increasing depth, the potential for geothermal utilisation decreases. In total, 76% of all values at temperatures between 10°C and 45°C are suitable for geothermal use. The Buntsandstein aquifer in the northwest and in the northeast of Bavaria as well as around Nürnberg is particularly well suited for aquifer storage due to the increased hydraulic conductivity together with temperatures around 20°C. Somewhat further north near Erlangen the temperature reaches even up to 27°C. However, in the northeastern and northwestern parts of the basin margins the temperature is only about 10°C. Keuper aquifers are suitable for energy storage in the regions north and south of Nürnberg at shallow depths, where they reach temperatures of about 15°C. However, the temperature decreases to about 10°C in the southwest.



Mon: 51
Topics: 8b) Deep subsurface groundwater systems

Developing a three-dimensional hydrogeological model based on the Konrad-site as an example to calculate the density-driven flow in deep groundwater systems

Torben Weyand, Jürgen Larue

Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH, Germany

In early long-term safety analyses for repositories for radioactive waste, the transport behavior of contaminants was examined based on the assumption of a freshwater groundwater system. Due to limitations in computer speed and capacity, the calculation of density-driven flow considering variations in salinity was not possible for large model domains over long simulation times. To date this still represents a geoscientific challenge.

This study contributes a three-dimensional hydrogeological model, considering several multi-aquifer-formations. The Konrad-site is used as an example to set up the model and is characterized by deep aquifers with high salinities, and a site-specific linear salinity gradient with increasing depth. The hydrogeological model takes up to 23 different geological layers into account, with several confined aquifers as potential migration paths for contaminants. The three-dimensional model is mainly based on subsurface contour maps of 15 different geological layers. Additionally, 30 two-dimensional vertical cross sections are used to validate the model. Hydraulically dominated fault zones and important geotectonic structures (salt domes) are considered to refine the model grid at specific locations.

To establish the model and further simulate the groundwater flow, the “Simulation of Processes in Groundwater” (SPRING) code is used. SPRING is suited for multidimensional hydrogeological modeling of density-driven groundwater flow through porous media considering variations in salinity. In previous studies, the density-driven flow was calculated based on representative two-dimensional cross sections also using data of the Konrad-site as an example.

In previous studies, the development of the salinity gradient over time was depicted by calculating the density driven two-dimensional flow in deep groundwater systems over long simulation times. These calculations showed that the salinity gradient measured at the site at present, can be described by long-term hydrogeological and geochemical processes of dilution and transport of saline solutions forced by the recharge of freshwater from the surface. Furthermore, the present salinity gradient at the site describes a snap-shot of a transient salt distribution in the long term, which is also interesting for the long-term stability of engineered barriers of a deep geological disposal.

Future work of this study intends to extend the numerical simulations by using the described three-dimensional model and analyze the groundwater flow in deep groundwater systems in more detail. The challenge is to develop a complex model grid with the ability to perform long-term safety analyses for large model domains over long simulation times within an adequate simulation time frame.



Mon: 52
Topics: 8b) Deep subsurface groundwater systems

Reactive Reservoir Systems - Crystal Nucleation and Filter Processes in Geothermal Systems

Philipp Zuber1, Sascha Frank2, Jürgen Schreuer1, Stefan Wohnlich2

1Crystallography, Ruhr-University Bochum, Germany; 2Hydrogeology, Ruhr-University Bochum, Germany

During geothermal energy generation, the change of temperature and pressure conditions can lead to supersaturation of the extracted fluids and thus to precipitation of minerals. Well-documented crystalline deposits on the inner walls of pipes are the consequences. In addition, turbulence-induced inhomogeneities and mechanical disturbances also lead to the formation of spontaneous free-floating crystal nuclei. A significant part of them are carried along and reinjected into the reservoir. There, the crystal nuclei are possible centers for crystallization and cementations processes or can accumulate by filter effects. Both processes contribute to scaling effects which limit the use of the geothermal reservoir. So far, such effects have not been considered in hydrogeochemical modelling programs, which are mainly based on the temperature and pressure dependence of solution and reaction equilibria in the reservoir.

Our investigations focus on a better understanding of the formation and growth of crystal nuclei in saturated geothermal solutions during thermal and pressure relaxation, and the development of approaches to control crystal nucleation and to minimize filter processes in the reservoir. For this purpose, a high-pressure high-temperature apparatus is used which is based on the working principle of a natural geothermal system. Two separate heating thermostats allow different temperatures to be used in the storage tank of the system and in the pressure vessel in which the rock sample is placed. Furthermore, we have the possibility to inject specific crystal seeds to study the influence of various minerals and their morphologies. Our setup allows pressures of up to 200 bar and temperatures of up to 100 °C. In addition to the determination of hydrochemical parameters, the crystallites and cements produced are characterized by optical methods, scanning electron microscopy and electron microprobe.



Mon: 53
Topics: 9a) Natural Hazards like earthquakes, landslides, floods and sea-level changes

Quaternary Tectonics of the Kalabagh fault, Sub Himalayas- insights from field studies, GPR and topographic analysis.

Wahid Abbas1,2, Sajid Ali1,2, Klaus Reicherter1

1Neotectonics and Natural Hazards, RWTH Aachen University, Lochnerstr.4-20, 52056 Aachen, Germany.; 2Department of Earth Sciences, COMSATS University Islamabad, 22060 Abbottabad, Pakistan.

The Salt Range and the Potwar Plateau marks the southern margin of Himalayas in Pakistan. Lateral extension of the Potwar plateau is controlled by strike slip faults. The Kalabagh fault marks the western margin of the Potwar plateau. It is 120 kilometers long dextral strike slip fault (McDougall and Khan 1990). In this study tectonics and morphology along the central segment of the fault, from Khairabad to Ghundi, have been investigated. Change in topography from Mianwali reentrant in the west to ramp in the east, marks Kalabagh fault zone. Friable Permian sandstone and sheared limestone mark the frontal face. Due to industrial excavations and erosive nature of the rocks, it is a bit challenging to find some classic movements or fault kinematics. Surface expressions of faulted quaternary alluvial deposits and pressure ridges have been observed. Near Khairabad and Ghundi, movements in quaternary strata have been found. Remote sensing data analysis shows deflection in streams that justify the right lateral movement. However, clear alluvial fan offsets have not been observed. But antithetic alignment of the pebbles in incised channels show back tilting due to compression. GPR data show subsurface structures striking parallel to the fault near Khairabad. Fractured pebbles in the trenches and road cuts in quaternary sediments indicate strain developed in recent deposits. Morphological evidences, GPR data, trench and excavation analysis concludes the Kalabagh fault as an active fault. Stress direction is inferred to be SW-NE. That splays out the structures N40°W to N50°W to the western side of the fault near Khairabad.



Mon: 54
Topics: 9a) Natural Hazards like earthquakes, landslides, floods and sea-level changes

AD 1755 tsunami backwash deposits offshore – the biomarker perspective (METEOR cruise M152)

Piero Bellanova1,2, Mike Frenken1,2, Jan Schwarzbauer1, Björn Deutschmann3, Pedro Costa4, Helmut Brückner5, Juan Ignacio Santisteban6, Jannis Kuhlmann7, Andreas Vött8, Klaus Reicherter2

1Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Germany; 2Neotectonics and Natural Hazards Group, RWTH Aachen University, Germany; 3Institute for Environmental Research, RWTH Aachen University, Germany; 4Instituto Dom Luiz, Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Portugal; 5Institute of Geography, University of Cologne, Germany; 6Department of Geodynamics, Stratigraphy and Palaeontology, Fac. Geological Sciences, Complutense University of Madrid, Spain; 7MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany; 8Institute of Geography, Natural Hazard Research and Geoarchaeology Group, Johannes Gutenberg-Universität Mainz, Germany

The deposition mechanics of tsunamis and the preservation potential of their residues in offshore areas are as yet virtually unknown. This is mainly due to the limited access to offshore archives as well as the negligible societal effect of tsunamis offshore. Therefore, tsunami research has focused on accessible, mainly sandy onshore, accumulations. However, the focus is shifting since new high-resolution methods have been developed, and the mere identification of sand sheets has reached its limits in answering today’s tsunami-related research questions.

The RV METEOR cruise M152 solely focused on the investigation of offshore sedimentary archives for the identification of tsunami deposits. The Algarve coast served as a perfect study area, since it had been affected by the AD 1755 Lisbon tsunami, and numerous onshore studies had detected its geologic footprint. During the M152 cruise, a total of 19 vibracores had been recovered from the shelf up to a water depth of 100 m. Within the offshore Holocene lithostratigraphic record, up to four tsunami candidates were identified based on their sedimentological and micropaleontological properties, which differed significantly from the normal shelf sediments. Additional geochemical sampling took place for inorganic (XRF) and organic analyzes. From the latter, source-specific and indicative organic compounds were extracted using Ultra-Turrax® extraction and alkaline hydrolysis, and then analyzed via GC-MS.First results from biomarkers, such as n-alkanes, fatty acids and ketones, indicate that event layers contain more terrestrial input than the background sediments, which leads to the assumption that run-off and backwash of a respective paleo-tsunami transports terrestrial material far offshore onto the shelf and possibly even deeper.



Mon: 55
Topics: 9a) Natural Hazards like earthquakes, landslides, floods and sea-level changes

Calculation for the transport of dust by the wind: from what particle size is this not possible, any longer?

Ludwig Biermanns

Universitaet Tuebingen, Germany

The speed, from where loose soil material begins to be transported by the wind, through deflation from a smooth ground, is the critical drag velocity (eq.1).

Dust is classified in heavy (1.0 to 0.1mm); settling, (0.1 to 0.001mm), suspended (< 0.001mm), and in fine dust (< 0.003mm).

At 0.25mm in particle-size diameter, the fluid threshold-wind velocity for transport (deflation by saltation) of particles makes 0.23m/s, as calculated example. When particle size increases, higher wind speeds are necessary for transport of dust or sand, of which the critical drag velocity for the fluid threshold is calculated:

v*crit = A × [g × d × ((ρpartρa)/ρa ) ]0.5 . (Bagnold, 1941: 86; 88; 101) (1)

v*crit = critical drag velocity [m/s];

A = 0.1 (reference value for fluid threshold (air, from where deflation of particles by

saltation begins));

g = 9.8062m/s2 (gravitational acceleration);

d = particle-size diameter [m], (e.g.: 0.002 mm = 2×10-6m);

ρpart = density of particle [kg/m3] (quartz grain: 2650kg/m3; standard value);

ρa = 1.204041kg/m3 for 20°C (density of dry atmospheric air, standard value).

From a diameter of 0.25mm and less, wind speed for the transport of particles does not decrease as calculated, any more; from 0.06 mm and less, critical drag velocity, even, rises for transport of dust, again.

Wind velocities for dust transport rise, when particles get smaller, because cohesive effects among particles increase, which hamper their uptake and transport from the ground by the wind. Reason for it is a rising ratio of clay, compared to the quartz minerals. Moreover, at decreasing particle size, fluid viscosity of the air is dominated by inertial effects of dust, because the density of the particles reach ca. 2000 times of that one from the air (cf. ρpart, ρa). Sand, with speed, acts like bullets on dust. Significantly finer-grained particles, in their turn, first, are struck, dislocated from their place, distributed in the air by the bigger particles, and finally, finer dust is blown away by the wind. Displacement of particles by wind itself, however, is less possible, when they get smaller (Bagnold, 1960: 360 – 362).

Bagnold, R.A. (1941): The … – 265 p., Chapman & Hall Publ., London.

Bagnold, R.A. (1960): The … – International Journal of Air Pollution, 2: 357 – 363.



Mon: 56
Topics: 9a) Natural Hazards like earthquakes, landslides, floods and sea-level changes

Organic geochemical signatures of the 2011 Tohoku-oki tsunami deposits (Northern Japan)

Mike Frenken1,2, Piero Bellanova1,2, Madeleine Wörner2, Verena Bischoff2, Jan Schwarzbauer2, Klaus Reicherter1

1Neotectonics and Natural Hazards Group, RWTH Aachen University, Germany; 2Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Germany

Misawa, located in the Aomori Prefecture in Northern Japan, was heavily damaged by the Tohoku-oki tsunami induced by the 2011 earthquake off the Pacific coast of Tohoku (9.1 MW). The tsunami, with wave heights of 6 – 10 m, inundated wide areas of the coastal lowland, causing massive damages to Misawa harbor and the associated infrastructure, releasing pollutants into the nearfield environment. Furthermore, field observation showed that trash and potentially hazardous objects (such as with paint and chemical-filled barrels) were transported into the coastal defense forest, deposited in backwash direction and serve as long-term sources of pollutants released in the environment.

The geochemical signature in the obtained sediment cores indicates a distinct identification of the tsunami layer. Both, anthropogenic marker (e.g. polycyclic aromatic hydrocarbons, pesticides and halogenated compounds) and biomarker (e.g. ketones) are significantly enriched in the visible sand deposits indicating the tsunami layer. Concentration increases of anthropogenic markers are detectable as well in deposits appearing as organic-rich layers first emerging on top of the sandy tsunami deposit and increasing in thickness further inland. This layer deposited during the tsunami inundation due to eroding of increasing amounts of organic material the further inland (e.g. loose plant material and wood), can be interpreted as an “invisible” tsunami layer. Biomarkers (in this case n-alkanes) indicate higher marine input in the tsunami layer.

Organic geochemical markers also correlate with this observation concluding that the 2011 Tohoku-oki tsunami serves as a blueprint for the development of high-resolution geochemical applications in order to gain more information than standard techniques, as most of them only rely on sand deposits as marker for inundation distances from the beach.



Mon: 57
Topics: 9a) Natural Hazards like earthquakes, landslides, floods and sea-level changes

Earthquake damage recorded along the Roman Eifel Aqueduct (Lower Rhine Embayment, Germany)

Sabine Kummer1, Gösta Hoffmann1,2, Rosa Enrique Martinez1, Mario Valdivia Manchego1

1University of Bonn, Germany; 2RWTH Aachen University, Germany

The Lower Rhine Embayment and adjacent areas are characterised by neotectonic deformation resulting in differential crustal movement. Slip rates along the fault systems are very low (< 0.1mm/a). Significant earthquakes are known to have occurred in the past but the faulting behaviour is not adequately known which hampers the risks assessment. We analysed the archaeological record of the largest Roman aqueduct north of the Alps. This so called aqueduct is 95.4 km long, has its source in the Eifel mountains and supplied the ancient city of Cologne with calcareous fresh water. The aqueduct crosses major faults of the Lower Rhine Embayment perpendicular.

Analyses of the aqueduct´s gradient gives weak evidence for creep along the Kirspenich Fault resulting in differential movement of hanging and foot wall in the order of a few centimetres. Vertical offsets of 15 and 35 cm are documented exactly where the aqueduct crosses the Holzheim Fault system close to the city of Mechernich. Here, also structural damage of the aqueduct is recorded and archaeological evidence exists for repair works on the aqueduct. We interpret these observations as well as the construction of a 4 km long deviation as necessary measures to keep the aqueduct operational after earthquake damage. The timing of the event falls within the period of aqueduct operation which is reconstructed to be between 80±10 CE to 270±10 CE. Supporting evidence for earthquake activity within this period is seen in the roof collapse of the nearby Kakus cave.



Mon: 58
Topics: 10a) Minerals in the depths: an experimental approach

Atomic structure and theoretical IR spectra of amorphous SiO2 at high pressures from first-principles molecular dynamics simulations

Johannes Stefanski1, Clemens Prescher1,2, Sandro Jahn1

1Universität zu Köln, Germany; 2DESY Hamburg, Germany

SiO2 is the most abundant and fundamental oxide component in the Earth. Further, it is a useful and essential material in industrial processes and in daily life. Recently, several studies have been carried out to investigate changes in the atomic structure of amorphous SiO2 and its structural analog GeO2 as a function of pressure up to 200 GPa using state-of-the-art experimental and computational methods.1,2,3,4 Some of those studies arrive at different conclusions regarding the changes of silicon and germanium coordination numbers with respect to oxygen beyond six-fold coordination with increasing pressure.

In this study, we use first-principles molecular dynamics simulations to model the atomic structure of amorphous SiO2 at room temperature and four different pressure conditions (4, 40, 200 and 576 GPa). The simulation boxes contain 264 atoms (88 SiO2 units). We find a good agreement between the structure factors S(Q) from x-ray diffraction experiments2 and our simulations. Additionally, we used the Voronoi dipole moments5 to compute IR spectra. The shape of the theoretical spectra is similar to experimental results from Williams and Jeanloz6 up to 40 GPa. Further, the frequency shifts of the main bands with pressure follow the Si-O bond length change related to the coordination changes in the glass. Specifically, we observe a frequency shift of the main band to >1100 cm-1 at 200 GPa with increasing proportion of sevenfold coordinated Si. We expect that we can use the computed spectra as fingerprint for future high-pressure experiments to investigate structural transformations in amorphous SiO2.

[1] Murakami, M. & Bass, J. D., Phys. Rev. Lett. 104, 025504 (2010)

[2] Prescher, C. et al., Proc. Natl. Acad. Sci. 114, 10041-10046 (2017)

[3] Petitgirard, S. High Press. Res. 37, 200–213 (2017)

[4] Spiekermann, G. et al., Phys. Rev. X 9, 011025 (2019)

[5] Thomas, M., Brehm, M. & Kirchner, B. Phys. Chem. Chem. Phys. 17, 3207–3213 (2015)

[6] Williams, Q. & Jeanloz, R., Science 239, 902–905 (1988)



Mon: 59
Topics: 10a) Minerals in the depths: an experimental approach

Goethite decomposition at the lower mantle conditions

Egor Koemets1, Maxim Bykov1,3, Georgios Aprilis2,3, Timofey Fedotenko2, Stella Chariton1, Elena Bykova1, Saiana Khandarkhaeva1, Iuliia Koemets1, Marcel Thielmann1, Catherine McCammon1, Natalia Dubrovinskaia2, Leonid Dubrovinsky1

1Bayerisches Geoinstitut (BGI), Universität Bayreuth, Germany; 2Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography, Universität Bayreuth, Germany; 3Photon Science, Deutsches Elektronen-Synchrotron, Hamburg, Germany

Starting from approximately 3 billion years ago (Gy) until the Great Oxidation Event (GOE, about 2.5 Gy ago) the Earth was inhabited with anoxygenic prokaryotes that oxidized iron as a result of their vital functions (1, 2). Oxidized iron species, or rust, contained as a major component FeOOH, and were buried on the ocean floor (1, 2). As the plate tectonics started approx. 2.8 Gy ago (3), rust-bearing sediments began immersion into the Earth mantle with subducting slabs, and eventually experienced high pressures and temperatures. We studied the behavior of goethite, FeOOH, by means of in situ single crystal X-ray diffraction at pressures up to 82(2) GPa and temperatures 2300(100) K. At conditions corresponding to even coldest slabs, at the depth of about 1000 km, FeOOH decomposes forming various iron oxide phases (Fe2O3, Fe5O7, Fe7O10, Fe6.31O9) and producing oxygen-rich fluid. Thus, our results suggest that recycling the rust in Earth mantle could contribute to oxygen release in the atmosphere, and explain the sporadic increase of oxygen level before GOE linked to the formation of Large Igneous Provinces(4).

1. D. E. Canfield, M. T. Rosing, C. Bjerrum, Early anaerobic metabolisms. Philos. Trans. R. Soc. B Biol. Sci. 361, 1819–1834 (2006).

2. S. A. Crowe et al., Atmospheric oxygenation three billion years ago. Nature. 501, 535–538 (2013).

3. O. Nebel et al., Geological archive of the onset of plate tectonics. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 376, 20170405 (2018).

4. U. Söderlund et al., Timing and tempo of the Great Oxidation Event. Proc. Natl. Acad. Sci. 114, 1811–1816 (2017).



Mon: 60
Topics: 10a) Minerals in the depths: an experimental approach

The effect of carbon and silicon on the strength of iron alloys: Implications for anisotropy in the Earth’s inner core

Ilya Kupenko1, C. Sanchez-Valle1, M. Achorner1, M. Krug1, J. Chantel2, E. Ledoux2, X. Ritter1, A. Rigoni3, H.-P. Liermann4, S. Merkel2

1University of Münster, Germany; 2Unité Matériaux et Transformations, CNRS, Université de Lille, France; 3Materialphysik, University of Münster, Germany; 4Photon Science, DESY, Hamburg, Germany

The cores of terrestrial planets are comprised of Fe-Ni alloys, with around 4-7 wt% of the light element(s) that account for the observed core density deficiency and reduced seismic velocity compared to pure Fe-Ni. Carbon and silicon are both considered as major light elements of the core: both have high cosmic abundance and can be efficiently incorporated into iron-nickel metal during core formation Moreover, the (Mg/Si) ratios of the mantle are inconsistent with those of the chondrites and the ‘missing’ silicon could be hosted in the core as Fe(Ni)-Si alloys.

Additionally to the average velocities mismatch, there is evidence for prominent anisotropy in the inner core, with the compressional waves traveling through the core faster in the equatorial plane than along the polar axis. The anisotropic structures in the inner core are likely formed by dynamic processes that induce the plastic deformation and development of textures of inner core materials under pressure. Yet, the effect of light elements on the plasticity of iron is poorly known, although this information is crucial for understanding how planetary cores deform.

Here we investigate the plastic deformation of hcp-Fe-Si and Fe-Si-C alloys up to 280 GPa and 180 GPa respectively at room temperature employing a technique of radial x-ray diffraction in diamond anvil cells. We utilize the radial diffraction patterns in order to map the development of texture in the sample and the dominant deformation mechanisms of the alloys. We will present the analysis of measured data and discuss their potential application to constrain plastic deformation in the cores of the Earth and other terrestrial planets.



Mon: 61
Topics: 10a) Minerals in the depths: an experimental approach

Phase stabilities and elemental redistribution processes between magnesite and mantle silicate at conditions of the lower mantle.

Lélia Libon1, Max Wilke1, Georg Spiekermann1, Karen Appel2, Bernd Wunder3

1Universität Potsdam, Germany; 2European XFEL; 3Deutsches GeoForschungsZentrum (GFZ)

Diamonds from the lower mantle are carrying, in their inclusions, important information from the deep interior to the Earth’s surface. Next to the expected minerals of lower mantle conditions (Mg-Fe-Al silicates and Mg-Fe oxides), these ultra-deep diamonds contain inclusions of carbonates and give proof of the presence of carbonates in the Earth’s lower mantle. In addition, these carbonate-bearing inclusions show high REE enrichment (e.g. Brenker et al. 2007) and thus raise questions about the role of carbonates as possible trace-element carriers in the Earth’s mantle.

Carbonate stabilities at high pressure and temperature have been intensively studied the last two decades. However, the stability of carbonates in presence of mantle silicates at deep mantle conditions remains unclear. Experimental studies support that magnesite (MgCO3) in absence of other mineralsis stable at P-T conditions corresponding to the lowermost mantle (>110GPa). A reaction between magnesite and silica at lower mantle conditions may lead to formation of bridgmanite and CO2. By increasing P-T conditions along the isotherm further in diamond anvil cell experiments, CO2 breaks down to form diamond and oxygen. This decomposition could indicate that the reaction of magnesite with silicate could be related to diamond formation in the lower mantle. To better constrain the stability of magnesite in the deep Earth, reactions must be studied in a chemical system which includes selected silicate phases of close-to-natural compositions. To achieve this aim, we will perform multianvil press and laser-heated diamond anvil cell (LH-DAC) experiments to investigate the reaction between magnesite and the silicate phases. In these experiments, magnesite will be reacted with two silicate glasses, enstatite-ferrosilite and haplobasaltic composition, respectively, at conditions relevant to the upper lower mantle (20-40GPa and 1500-2500K).

Additionally, the same reaction will be investigated with Sr/La/Eu-doped materials to show the trace element re-distribution between silicate phases and magnesite. One of this series is planned to be done with Sr/La doped-magnesite as starting materials. Consequently, the first step was to investigate the solubility of these trace element in magnesite. Reaction between strontianite (SrCO3) and magnesite leads to formation of Sr-dolomite (Sr0.5Mg0.5CO3) + MgCO3 with a Sr content in magnesite below the detection. Whereas, reaction of La2(CO3)3 * nH2O with magnesite leads to the formation of La-bearing magnesite with La content of 1.5wt% in average + a lanthanum carbonate phase (LaCO3OH).

Brenker, et al (2007). Carbonates from the lower part of transition zone or even the lower mantle. EPSL, 260(1-2), 1-9.



Mon: 62
Topics: 10a) Minerals in the depths: an experimental approach

Towards a systematic interpretation of Mg L-edge X-ray Raman scattering spectra of compressed amorphous magnesiosilicates

Georg Spiekermann1, Sylvain Petitgirard2, Christian Albers3, Keith Gilmore4, Christoph J. Sahle5, Christopher Weis3, Manuel Harder6, Christian Sternemann3, Max Wilke1

1Universität Potsdam, Germany; 2ETH Zürich, Switzerland; 3TU Dortmund, Germany; 4Brookhaven National Lab, USA; 5ESRF Grenoble, France; 6DESY Hamburg, Germany

MgSiO3 glass at high pressure is investigated as a proxy to ultramafic silicate melts originating from the Earth’s mantle. Its atomic structure is intimately linked to macroscopic properties such as density and viscosity [1].

The structural complexity of this glass at high pressure and the similarity of the Si-O and Mg-O partial radial distribution functions make it desirable to apply additional, element-specific measurement techniques in addition to X-ray diffraction [2]. The method of choice is X-ray Raman scattering (XRS) spectroscopy [3,4], which is the only spectroscopic technique to access the electronic structure of light elements like O, Si and Mg in a confined environment like a diamond anvil cell [5].

We present measured and computed Mg L-edge XRS spectra of magnesiosilicate minerals and MgSiO3 glass up to 60 GPa. Spectra are computed via Bethe-Salpeter calculations with the OCEAN code [6].

A systematics of Mg L-edge X-ray spectra will allow us to yield unprecedentedly direct insight into the structural changes in MgSiO3 glass at high pressure.

References

[1] - Y. Kono and C. Sanloup (eds.): “Magmas under Pressure – Advances in High-Pressure Experiments on Structure and Properties of Melts”, Elsevier Amsterdam (2018)

[2] - Y. Kono, Y. Shibazaki, C. Kenney-Benson, Y. Wang and G. Shen: “Pressure-induced structural change in MgSiO3 glass at pressures near the Earth’s core–mantle boundary”, Proceedings of the National Academy of Sciences, 115(8), pp. 1742-1747 (2018)

[3] – H. Fukui and N. Hirakoa: “Electronic and local atomistic structure of MgSiO3 glass under pressure: A study of X-ray Raman scattering at the silicon and magnesium L-edges”, Physics and Chemistry of Minerals (2017)

[4] S. K. Lee et al.: “X-ray Raman scattering study of MgSiO3 glass at high pressure: Implication for triclustered MgSiO3 melt in Earth’s mantle”, Proceedings of the National Academy of Sciences, 105(23), pp. 7925-7929 (2008)

[5] C. Sternemann and M. Wilke: “Spectroscopy of low and intermediate Z elements at extreme conditions: in situ studies of Earth materials at pressure and temperature via X-ray Raman scattering”, High Pressure Research, 36:3, pp. 275-292 (2016)

[6] Gilmore et al.: “Efficient implementation of core-excitation Bethe-Salpeter equation calculations”, Computer Physics Communications, 197, pp. 109 (2015)



Mon: 63
Topics: 10a) Minerals in the depths: an experimental approach

Phase relations of Al-bearing MgFe2O4: Implications for natural occurences in diamond

Laura Uenver-Thiele1, Alan Woodland1, Tiziana Boffa Ballaran2, Nobuyoshi Miyajima2

1Institut für Geowissenschaften, Universität Frankfurt; 2Bayerisches Geoinstitut, Bayreuth

Spinel-structured phases commonly occur as inclusions in diamond [e.g.1,2,3]. Depending on their composition (e.g. MgAl2O4 [4], MgFe2O4 [5], FeFe2O4 [6]) their phase relations at high-P and T can differ significantly from each other. MgFe2O4-FeFe2O4 spinels are of special interest because of their ability to store Fe2+ and Fe3+, making them redox-sensitive. Thus, they can act as indicators for P, T and redox conditions during entrapment. For example, magnesioferrite can occur in (Mg,Fe)O inclusions in diamond and has been interpreted to have either directly exsolved from (Fe,Mg)O in the upper mantle or formed from a precursor phase (e.g. (Mg,Fe)2Fe2O5, hp-(Mg,Fe)Fe2O4, (Mg,Fe)3Fe4O9 at higher P [5,7]. However, natural magnesioferrite can also contain small amounts of Al and its effect on phase stabilities is currently unknown.

This study is aimed to investigate the post-spinel phase relations in multi-component spinels approaching natural compositions [i.e. (Mg,Fe2+)(Fe3+,Al)2O4] and to place constraints on the origin of such phases, as they are associated with diamond formation. Multi-anvil experiments are conducted between 8-22GPa and 1000-1600°C with several bulk compositions. Run products were analysed by EPMA, XRD and TEM. Preliminary results show that the “spinel” phase can be stabilized to higher pressure (with increasing T) depending on the amount of Al, but is limited to max. ~16 GPa (at 1600°C). Importantly, Mg2(Al,Fe)2O5 becomes stable between 16-21GPa over a wide temperature range, making this post-spinel phase more relevant for mantle conditions compared to the Mg-Al endmember Mg2Al2O5 [>2100°C at 20 GPa (4)]. At even higher P and T ≥ 1300°C, a hp-polymorph with M3O4 stoichiometry becomes stable. Phase relations of Fe2+-rich compositions seem to differ from those containing significant amounts of Mg and involve other hp-phases such as those with an M7O9 stoichiometry.

[1] Kaminsky et al. (2009) Min Mag, 73, 5, 797-816.
[2] Kaminsky (2013) Can Mineral, 51, 669-688.
[3] Palot et al. (2016) Lithos, 265, 237-243.
[4] Enomoto et al. (2009) J Solid State Chem 182, 389-395.
[5] Uenver-Thiele et al. (2017a) Am Min 102, 632-642.
[6] Woodland et al. (2012) Am Min 97, 1808-1811.
[7] Uenver-Thiele et al. (2017b) Am Min 102, 2054-2064.



Mon: 65
Topics: 12a) New Models for Old Deposits

Exploration, deposit evaluation and first economic information about a spodumene pegmatite in Canada Ontario

Stephan Peters, Florian Lowicki, Florian Beier, Jana Rechner, Torsten Gorka

DMT GmbH & Co. KG, Germany, Essen

The since 1952 known Spondumene Pegmatites [1] were since that time explored three times. In the years 1955 until 1957 the first drill holes were drilled and a first shaft were sunken. In the years 2008 until 2011 a second exploration phase with more drill holes were undertaken. The last exploration phase starts in 2017. Actual a new deposit evaluation is on the way. Additional drill holes, channel samples and sample analyses are currently under investigation. A new 3D Model is under construction and first mining options are under investigation. The strike length of the pegmatites at the surface is in between 50 m up to 1.8 km. The thickness varies in between 1 to 10 m.

The majority of the pegmatites are hosted by metasediments or biotite granite. Spondumene is the dominant Li-bearing mineral in all of these pegmatites. The pegmatite dyke internal zonation is in general a granitic or aplitic border zone and a spondumene, albit and quarz center zone. In some cases there are more or less aplite layer and sometimes quarz tourmaline veins occur.

The mineralisation consists of coarse-grained fresh pale green spondumene crystals oriented perpendicular to the strike of the pegmatite dyke. In the field the spondumene minerals were often in the size of fingers. In some areas the length of these crystals is up to 1 m and a thickness of up to 12 cm.

A bulk samples has been taken and first processing investigations have been done.

Today the investigation is focused in the northern areas were several spondumene pegmatites occur at the surface relatively near to each other. There are 5 pegmatites which were now new modelled in 3D. The drill holes hit the pegmatites in the maximum depth of 350 m below the surface. The distances of the drill holes is below 50 m. More than 200 drillholes were drilled in the area. The lithium oxide contend of the core samples varies from low up to 2,7% (Li2O). The actual 43 101 NI resource statement and the PEA is uploaded to the sedar webside of the Toronto stock exchange.

The next steps are the pit optimisation and more in detail geotechnical investigations about the stability of the rock mass. In general the environment and the water situation was also under investigation.

The project will be shown in the actual situation and the newest exploration results will be displayed.



Mon: 66
Topics: 12b) Mineral deposits of societal relevance for Europe

GeoERA – Geological Survey Organisations contribution to Europe’s raw materials sustainability

Antje Wittenberg1, Daniel de Oliveira2, Tom Heldal3, Francisco Javier González4, Lisbeth Flindt Jørgensen5

1BGR, Germany; 2LNEG, Portugal; 3NGU, Norway; 4IGME, Spain; 5GEUS, Denmark

Mineral Raw Materials are essential for societal development and Europe’s ambition for economic growth and well-being. Being the front-end of the value chain, secured supply of sustainably produced mineral raw materials is of vital importance to meet the UN Sustainable Development Goals (e.g. for the energy transition of the society in large and the energy demanding industry in particular to be realised locally). With initiatives and actions such as the Raw Materials Initiative, the EIT Raw Materials and the European Battery Alliance the European Union, Research Organisations and the European Industry focus on:

  • The security and sustainability of mineral raw materials supply from EU sources; and
  • The management of competing uses of the European surface and subsurface.

Through the four GeoERA Raw Materials projects EuroLITHOS, FRAME, MINDeSEA and Mintell4EU more than 30 National and Regional Geological Survey Organisations (GSO) from Europe and beyond serving those societal needs mentioned above. Shared expertise and information adds to the EU Raw Materials Knowledge Base by addressing sustainable supply of Mineral Raw Materials from European on- and off-shore resources.

EuroLITHOS gives specific attention to ornamental stone resources for which Europe has a long tradition in mining, processing and usage. Increasing demand in maintaining cultural heritage sites and other construction works indicate the specific attention given.

FRAME designed to research the Strategic and Critical Raw Materials (SCRM) in Europe to gain new insights into reserves and resources taking in to account also new technologies and developments. Europe’s longstanding tradition in mining and its heaps and dumps will be investigated in view of SCRMs.

MINDeSEA focusses on exploration and investigation of SCRM from seafloor mineral deposits in European waters. GSO and Marine Institutes identifying areas for responsible resourcing and information on management and Marine Spatial Planning in European Seas are in its core of action.

Mintell4EU focusses on harmonizing data, providing spatial data and thematic maps. Updated electronic Minerals Yearbook and the extension of the spatial coverage and quality of data currently in the Minerals Inventory will be the final product.

Increased data quality and data harmonization on Europe’s raw material supply potential will provide valuable data publicly accessible through the GeoERA Information Platform and in line with the Raw Materials Information System the EU Science hub of the European Commission.

GeoERA (www.geoera.eu) is co-funded through the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166.



Mon: 67
Topics: 13a) 3D Geological Modelling and subsurface potentials

Step by step: The 3D subsurface model of Mecklenburg-Vorpommern is growing

Karsten Obst, Juliane Brandes, Sabine Matting, Jasmaria Wojatschke, Andre Deutschmann

Geological Survey of Mecklenburg-Western Pomerania, LUNG M-V, Germany

Different subsurface uses, e.g. hydrocarbon exploitation, natural gas storage, geothermal energy production, drinking water supply etc. may hamper each other at suitable locations. Therefore, a 3D underground model is needed to visualize the various resources and to support politicians and decision makers in spatial planning of the underground. The Geological Surveys of the north German federal states (SGD) are developing a 3D geological model of the North German Basin (NGB) in the project “Subsurface Potentials for Storage and Economic Use in the North German Basin” (TUNB), which was initiated by the Federal Institute for Geosciences and Natural Resources (BGR) and started in 2014.

The Geological Survey of Mecklenburg-Western Pomerania will model the northeastern part of the project area. The model comprises 13 major lithostratigraphic layers between bases of Zechstein and Rupelian. Besides, numerous tectonic faults and salt diapirs will also be modelled. The model is based on more than 750 deep wells and about 2,500 seismic lines. As the model area is with c. 25,000 km2 rather large, the modelling is done stepwise.

First, collaborative 3D modelling was applied in the border regions to neighbouring federal states. Typical reflector horizons that mark lithological surfaces close to stratigraphic boundaries were correlated with borehole profiles and modelled using the SNS workflow of SKUA-GOCAD. Salt diapirs and faults were mainly modelled by hand.

The model area of Mecklenburg-Western Pomerania is divided into 11 parts. The first part Ludwigslust was finished in 2017. The parts Waren, Pasewalk and Schwerin were finalized in 2018. In the first half of 2019, the parts Rostock and Neubrandenburg were completed. This means that more than the half of the project area was modelled. The model includes more than 90 faults at the Zechstein base, 11 diapirs and about 35 supra-salt faults, of which the major fault of Fresendorf-Goritz is the most prominent one with a length of approximately 50 km.

The next steps comprise modelling of the complex Western Pomeranian Fault System (WPFS) in the NE using reprocessed seismic lines and adjustment of the model horizons in the border region to Poland within GEO-ERA using also gravmag data.



Mon: 68
Topics: 13a) 3D Geological Modelling and subsurface potentials

Tectonic 3D-model of the Berga antiform – Saxo-Thuringian Zone

Franz Müller, Uwe Kroner

Technische Universität Bergakademie Freiberg, Germany

The “Bergaer Sattel” of the Saxo-Thuringian Zone of the Central European Variscides constitutes a NE-SW striking antiformal structure. The striking feature of the Berga antiform is the juxtaposition of greenschist facies metamorphic rocks with very low grade lithologies of Paleozoic age. Classically, the entire region is described as a simple southeast-vergent anticline without significant horizontal displacement. However, recent mapping revealed the existence of allochthonous units. To clarify aspects of the architecture, we generated a regional 3D model of the Berga antifom using the SKUA-GOCAD software package. The model results from the incorporation of existing datasets like geological maps and profiles in combination with the extensive acquisition of drilling data as well as the results of a tectonic mapping campaign. The width of the model is 50 km in NE-SW, 15 km in NW-SE direction and the depth is 1 km. Tectonically, we subdivide the Berga antiform in a par-autochthonous and an allochthonous unit, mainly exposed in the SW and the NE part of the antiform respectively. By construction of three stratigraphic horizons the par-autochthonous unit can be modelled as a southeast vergent fold structure. In contrast, the allochthonous unit is characterized by pervasive ductile deformation during low grade metamorphism. Subsequently, the metamorphic layering is affected by NW-SE shortening like the tectonics characteristic for the par-autochthonous unit. We explain the complex architecture of the Berga antiform as follows. Initial NE-SW shortening during the main stage of the Variscan collision led to crustal stacking of the Paleozic sequence. Separated by NE-SW striking tear faults, the future par-autochthonous domain remained in uppermost crustal levels. Due to dextral tranpression, subsequent exhumation of the allochthonous unit lead to overthrusting onto the NE part of the par-autochthonous unit. Late variscan compression culminates in SE vergent thrusting and folding of the entire structure. NW-SE oriented graben structures and N-S oriented strike slip zones resulted from tectonics in post-Variscan time.



Mon: 69
Topics: 13a) 3D Geological Modelling and subsurface potentials

More data - more Model. Experiences within the project TUNB.

Maik Schilling, Christoph Jahnke, Andreas Simon, Thomas Höding

Geological Survey of Brandenburg, Germany

The goal of the project TUNB (Subsurface Potentials for Storage and Economic Use in the North German Basin) is the production of a transnational structural geological 3D model of the North German Basin. Financed by the Federal Institute for Geosciences and Natural Resources, the state geological survey organizations of the federal states of Mecklenburg Western Pomerania, Saxony-Anhalt, Lower Saxony, Schleswig Holstein and Brandenburg are involved. Usually a number of different data are available for the generation of 3D models. In addition to the indispensable borehole data, these are primarily seismic test results in the form of maps and profiles as well as gravimetric investigations and geological maps. All these data were usually collected over a long period of time. Regarding the seismic investigations this period covers more than 50 years in Brandenburg. Within this period, the technique changed which made the measurement results more accurate, but the basics used to interpret the data also changed. Therefore, the stratigraphic assignment of seismic reflectors over time varies, resulting in discrepancies in the interpreted data between the various study campaigns. Furthermore, older data has been re-processed in recent times, which results in different interpretations compared to the original. All these data cannot be used for modeling without further editing. Based on new insights into the stratigraphic assignment of reflectors, drill holes and reliable seismic results, the entire dataset must be harmonized. Only then the heterogeneous data can be used for modelling purposes. Another aspect of data collection and harmonization is the necessary border matching of models. Within a country or between neighbouring federal states, this is usually possible with manageable effort. This is especially true for the states of the former GDR, since the data base is generally the same here. However, if one wants to compare a model with a model in the neighbouring state or carry out a cross-border modelling, the differences in the interpretation of the seismic data become even clearer. In a first data comparison along the German-Polish border, there are often differences in the assignment of the seismic reflectors. In a first step the seismic data in time domain are compared as well as the different speed models to match the seismic reflectors on both sides of the border.



Mon: 70
Topics: 13a) 3D Geological Modelling and subsurface potentials

Experience with the construction of a volumetric model in the German North Sea Sector

Björn Zehner

BGR - Federal Institute for Geosciences and Natural Resources, Germany

Many projects that deal with the construction of 3D structural models of the subsurface do not model the geological bodies (rock units) directly, but instead describe them indirectly by modeling and rendering the interfaces between these bodies (faults and horizons). Converting these surface-based models into volumetric models is necessary, if they are to be used for process simulation with finite elements or finite differences. Further, this type of model can be used to define and visualize arbitrary cross-sections through the model interactively and to extract important features and subregions in order to provide more intuitive visualizations.

In the past, we have described several workflows, involving the use of Skua-Gocad together with the external software packages Gmsh and TetGen, to construct a volumetric tetrahedral representation of the 3D geological subsurface starting from surface based structural models and further to provide a rastered version of the same model. In all these cases, the scenarios presented were structurally fairly simple and where based on an artificial model generated for demonstration purposes. Hence the performance of the suggested workflows needed to be tested using a much more complicated real-world model. The 3D geological model used for this study is a small 10x20 km large sub-region of the “Entenschnabel” in the German North Sea Sector which involves 16 horizons, 43 faults and two salt diapirs. In our contribution we will provide a short discussion on the workflows and share our experience with applying them to the real-world model.



Mon: 71
Topics: 13a) 3D Geological Modelling and subsurface potentials

On the visualization of 3D geological models and their uncertainty

Björn Zehner

BGR - Federal Institute for Geosciences and Natural Resources, Germany

3D visualization is important in order to communicate to customers and stakeholders or to the public the 3D geological models generated. Depending on the anticipated audience, the visualization should be presented in such a way that is easy to understand and intuitive. While this might be worth a discussion in its own right, the issue becomes even more complicated when not only the model itself needs to be shown, but also the certainty with which the subsurface is known. As part of a work package within the GeoERA – 3DGEO-EU project, different options to visualize this uncertainty are evaluated, and example data sets and workflows explaining the use of the suggested methods for 3D geological models will be provided in the near future.

We will briefly discuss the problems we see with the visualization that is currently state of the art for certain geological models and is used by software packages, such as Gocad or Petrel or different Web-Viewers. We will than show how this visualization might be improved and be easier to understand by using volume visualization, a technique that is common in medical visualization and for the visualization of 3D seismic data, but less commonly used for 3D geological models. Further we will discuss how bi-directional transfer functions (color tables) could be used for augmenting the shown 3D geological model with the information on how certain the position and orientation of a shown structural feature is.

Several examples that show how uncertain data could be rendered have been generated and pre-processed using Gocad and have been visualized using the publicly available software Paraview for scientific visualization. Further the open source software Blender for 3D content creation has been used to test the option of providing a more photorealistic rendering, including such effects as shadows and ambient occlusion. The methods and workflows described rely on open source software and are thus available to the 3D modelling community for free. However, in order to really investigate models and data interactively using Paraview and the suggested methods, some extensions would be needed for the visualization software itself.



Mon: 73
Topics: 13c) Tectonic Systems (TSK open session)

Retrograde tectonic activity in the Mont Blanc and Aiguilles Rouges Massifs dated through hydrothermal monazite

Christian A. Bergemann1, Edwin Gnos1, Martin J. Whitehouse2

1Museum of Natural History Geneva, Switzerland; 2Swedish Museum of Natural History, Stockholm, Sweden

Ion probe dating of mm sized hydrothermal monazite is a promising method for understanding the low-T deformational history of an area. The monazites crystallize in open alpine type fissures (clefts) where they occur as a late crystallization at temperatures of ca. 300/350 ºC. The crystals record the age of crystallization without risk of diffusional lead-loss at the prevalent temperatures. Through alteration due to partial dissolution-reprecipitation/recrystallization, the monazites further have the potential to record several phases of tectonic activity down to ca. 200 ºC or somewhat below.

The analysis of hydrothermal monazite from open clefts in the Mont Blanc and Aiguilles Rouges Massifs in the Western Alps reveal three major phases of tectonic activity. These occurred at 11.5–10.5 Ma, 9 Ma and 8–7 Ma, interpreted as (re)crystallization during the onset and continuation of dextral strike-slip faulting. Sub-horizontal clefts formed pre 11.5 Ma in a compressive regime and monazite from the horizontal clefts may thus record all three deformational phases. A comparison of monazite ages with thermochronometers indicates that the clefts along with the network of vertical shear zones in the Mont Blanc Massif became strongly overprinted at 11.5 Ma during a switch from transtensional to pure strike-slip deformation. During these strike-slip movements a younger generation of sub-vertical clefts formed along both sides of the Mont Blanc and in the Aiguilles Rouges Massif. This and associated fluid flow may have been diachronous, as primary monazite crystallization in vertical clefts from the Aiguilles Rouges Massif likely dates their formation to around 9 Ma.



Mon: 74
Topics: 13c) Tectonic Systems (TSK open session)

Elements of the Osning Fault Zone (NW-Germany) – Key Structures of a Strike-Slip Zone

Manfred Dölling, Günter Drozdzewski

Geologischer Dienst Nordrhein-Westfalen, Germany

The WNW - ESE (hercynian) trending Osning fault zone forms a more than 200 km long strike- slip zone, which separates the Lower Saxony Basin in the north from the Münsterland basin in the south. The structure and kinematics of the Osning fault zone are analyzed on the basis of strike-slip tectonics (Drozdzewski & Dölling 2018). This superordinate structuring of the dextral strike-slip zone is carried out by five synthetic, mostly left-kicking oriented sub-segments from the Gronau segment of the Netherlands in the northwest to the Falkenhagen segment of the Hessian Depression in the southeast. Between the individual segments W - E trending en echelon folds developed as connecting structures, such as the Rothenfelde, the Ochtrup and the Waldhügel anticlines, as a result of predominantly narrow crossovers. They can be used as evidence for an N - S oriented palaeostress field during the Late Cretaceous. At the Osning fault zone, the following structural elements are characteristic for the existence of strike-slip tectonics:

- echelon arranged, left-stepping fault elements as synthetic Riedel shears with convergent connection structures. The vertical components of the various strike-slip faults of the Osning fault zone vary between several hundreds and two thousand meters, whereas the horizontal components are much bigger with amounts ranging between 1.5 and 10 km.

- Cross faults as antithetic Riedel shears that were deformed during interaction with the dominant synthetic Riedel shears of the Osning fault zone (e. g. antithetic Bielefeld cross fault).

- Overlap structures (e. g. Ibbenbüren block as push-up, the Grotenburg block as pull-apart), formed between en echelon arranged faults by transpressional and transtensional movements. Occasionally, the overlap structures are associated with block rotations.

- Flower structures with partially low-dipping polar and bipolar faults in the upper floor and steep strike-slip faults in the lower tectonic level of the northwestern Osning fault zone.

Above all, the close temporal and spatial juxtaposition of compression and extension during Late Cretaceous inversion indicates shearing instead of temporal separate processes, as suggested for instance by Baldschuhn & Kockel (1999). In addition, several other elements of the Osning block and the interpretation of the Münsterland Basin as an asymmetrical strike-slip basin support the strike-slip character of the tectonic structures.

References:

Baldschuhn, R. & Kockel, F. (1999): Das Osning-Lineament am Südrand des niedersachsen-Beckens.- Z. dt. geol. Ges., 150 (4): 673 – 695.

Drozdzewski, G. & Dölling, M. (2018): Elemente der Osning-Störungszone (NW-Deutschland) – Leitstrukturen einer Blattverschiebungszone.- scriptum-online, 7: 39 S.



Mon: 75
Topics: 13c) Tectonic Systems (TSK open session)

The boundary between Eastern and Western Alps as seen from a foreland perspective – an example from the Miocene Molasse Basin

Martin Elsner

Erdwerk GmbH, Germany

The boundary between Eastern and Western Alps is commonly assigned to the valley of the Rhine south of Lake Constance. It is documented by the predominance of Helvetic units in the West (Switzerland) and Austroalpine units in the East (Austria and Germany). In the Western Alps and the westernmost part of the Eastern Alps (Vorarlberg, Allgäu), tectonic transport was orogen-normal towards the Foreland basin during the Miocene. In contrast, the Eastern Alps are cross-cut by orogen-parallel to oblique strike-slip faults, leading to an escape of the nappes to the east.

Boundaries in the adjacent North Alpine Foreland Basin (Molasse Basin) are less distinct. Some authors prefer a subdivision in Western, Central and Eastern Molasse Basin, while others classify a Western and Eastern part only. In any case, these are largely geographic definitions, though they do match geological reasonable positions at certain times. However, for the Obere Meeresmolasse (OMM, Ottnangian) and the Obere Süßwassermolasse (OSM, Karpatian to Pannonian), the following features point to a division into a Western and Eastern part, with a transition approximately along the river Lech:

  • grain size distribution within the OMM shows a minimum here and heavy mineral assemblages indicate different sources to the East and West
  • the position of the forebulge as indicated by the Albsteinschwelle is present only in the West
  • the Kirchberger Schichten as transitional member between OMM and OSM are most prominent to the East
  • the base of Nördliche Vollschotterserie/Geröllsandserie, a gravel bearing sequence within the OSM, is distinctly more inclined westward
  • the thickness of the Nördliche Vollschotterserie/Geröllsandserie and the presence and duration of hiatuses indicate overall lower subsidence rates eastwards
  • drainage pattern from the Miocene alpine streams indicate large fan structures westward (Hörnli-, Napf-, Hochgrat-Adelegg-Fan) and much smaller ones to the East

In relation to the boundary between Western and Eastern Alps, this position is shifted for around 80 km to the east, illustrating the relevance of tectonic processes in the orogenic wedge for foreland sedimentation: flexural loading of the orogen and asymmetric, wedge-like subsidence of the foreland in the West (including the westernmost part of the Eastern alps) contrasting lateral extrusion of the piled nappes and almost uniform subsidence of the foreland in the East. Fluvial streams of the OSM showed to be very sensitive to subsidence variations and the distribution of their sediments can be used for basin analysis.



Mon: 76
Topics: 13c) Tectonic Systems (TSK open session)

Structural geological study of a shear zone at the Stora Le Marstrand formation, island Arndorsholmen (SW Sweden)

Anna Friebel, Thomas Degen

Economic Geology and Petrology Research Unit, Institut of Geosciences and Geography, Germany

The geology in SW Sweden is strongly influenced by the Sveconorwegian orogeny (1.1-0.9 Ga). During this deformational event the Idefjorden Terrain was aggregated on the Baltic Shield and large crustal units have been sheared on Baltica and stacked on each other. These crustal units are mainly built up of meta-sediments (ca. 1.67 Ga) which have been intruded by several magmatic suits (1.5-0.9 Ga) of felsic as well as mafic to ultramafic compositions.

During field work northwest of Kungälv (SW Sweden) a north-south trending shear zone on the island Arndorsholmen has been mapped. The lithological units are dominated by migmatized supracrustals of the Stora Le Marstrand formation.

The shear zone has a vertical dip and divides the island in to two different parts. In the western part are high migmatized metasediments and in the eastern part consists of a complex mixture of different lithologies. Additionally, a mafic dyke crops out longside the shear zone. The dyke is 1.5 m thick and while the western rim is deformed and shows a foliation, the eastern rim is nearly undeformed. Furthermore, there are idiomorphic garnets visible in the dyke. The garnets can grow up to 3.5 cm in size. First field observations and microscopically investigations indicate that rocks in the area have been subject to different high metamorphic conditions. Therefor a granulite facies metamorphic overprint was proved in the migmatized metasediments. Additionally, metamorphic characteristic of amphibolite facies conditions, like newly formed biotite with a preferred orientation and growth of garnet, reveal one or more metamorphic overprints under this conditions. This study aims to model the deformation history of this area by tectonic data and cross sections. Furthermore, the different lithologies are analysed microscopically with special focus on shear sense indicators and streching lineation. Moreover, the grade of metamorphism was determined to reconstruct the p-T-conditions during this deformation.



Mon: 77
Topics: 13c) Tectonic Systems (TSK open session)

Slab hydration: combining constraints from oceanic plate structure and intraslab seismicity

Jacob Geersen1, Christian Sippl2

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; 2Institute of Geophysics, Czech Academy of Sciences

Most subduction-zones exhibit two bands of intraslab seismicity, the lower one situated at 20-40 km below the plate-interface within the subducting oceanic mantle. This band, which is usually referred to as the lower seismicity plane, runs parallel to the plate-interface and is characterized by rather low magnitude earthquakes showing downdip-extensive mechanisms. The intensity of lower-plane seismicity often varies greatly along a single subduction zone, and can be completely absent in some areas. To date, there is no single accepted physical model which explains the mechanism that drives earthquake occurrence within the lower-plane as well as observed spatial variations over relatively short distances. One hypothesis that has been put forward for explanation of the existence of the lower seismicity plane is that it results from serpentinite dehydration along the 600–650∘C isotherm in the oceanic mantle. Serpentinization possibly occurs in the outer rise region of oceanic trenches by water which infiltrates the oceanic crust and mantle along bending-related faults. If this hypothesis is correct, the intensity of lower-plane seismicity should correlate with the amount and penetration depth of water in the slab, and thus with the intensity and the depth extent of bending-related faulting. To test this, we correlate the occurrence and intensity of lower-plane seismicity in the North Chilean, Japan Trench, and Central American subduction-zones with oceanic-plate fault patterns in the outer rise and trench regions. To analyze the intensity of lower-plane seismicity, we compute the ratio between event numbers in the rather homogeneously active upper seismicity plane and the lower plane in along-strike distance bins. With this approach, we avoid the issue of variable earthquake catalog completeness that would complicate the analysis if absolute event numbers were used. Fault patterns are derived from a compilation of more than 100 ship-based bathymetric surveys complemented by published seismic reflection lines which run perpendicular to the individual margins. First results point towards a higher rate of lower-plane seismicity in regions where plate-bending is expressed in well-developed horst-and-graben structures as well as in regions where topographic features on the oceanic-plate enter the subduction-zone. Future work will further explore this possible correlation.



Mon: 78
Topics: 13c) Tectonic Systems (TSK open session)

Pre-Alpine tectonic and sedimentary contacts in the southeastern Ötztal Nappe (Austroalpine, Italy)

Linus Klug, Nikolaus Froitzheim, Frank Tomaschek, Markus Lagos

Rheinische Friedrichs-Wilhelms-Universität Bonn, Germany

In its southeastern part the Ötztal Nappe comprises the Ötztal Basement s. str., the Schneeberg Complex, the Laas Series and the Texel Complex. The latter is known as the western end of the Eoalpine High-Pressure Belt, for which several subduction and exhumation models exist. For assessing these models, it is essential to clarify the relationships inside the Ötztal Nappe.

Systematic electron-microprobe garnet mapping allows discrimination between different metamorphic histories in the southeastern Ötztal Nappe by zonation patterns. Alpine garnet growth is reported in all units. Variscan high-grade metamorphism is documented by inherited cores of two-phase garnets. While the internal parts of the Schneeberg Complex show only single-phase garnets, the Ötztal Basement s. str., the Laas Series and the Texel Complex show two-phase garnets. The Schneeberg Complex can be divided into the single-phase Schneeberg synforms and the two-phase Schneeberg frame zone (Rahmenzone). The tectonic contact between the Schneeberg synclines and the other units is therefore of pre-Alpine origin. Garnet zonation does not indicate an Alpine contact between the Texel Complex and the Ötztal Basement s. str. This challenges models where the Texel Complex and the Ötztal s. str. represent the footwall and hanging wall of an exhumation-related normal fault (Sölva et al. 2005) or two different nappe systems (Schmid et al. 2004).

To test if the remaining contacts are of sedimentary nature, we used detrital zircon U-Pb dating by laser ablation ICPMS. Previous U-Pb dating of magmatic zircons of granitic intrusions in the southeastern Ötztal Nappe yielded Ordovician (450 – 470 Ma) formation ages. Our set of detrital zircon ages indicates that the Austroalpine basement containing Ordovician magmatites is the source area of the metasediments of the Schneeberg Complex and the Laas Series. We suggest that the Schneeberg and Laas series represent the post-Ordovician, pre-Permian sedimentary cover of the Ötztal/Texel basement. In contrast to the Laas Series and the other units, the rocks presently found in the Schneeberg synclines belonged to a higher structural level of the Variscan orogeny, unaffected by Variscan garnet-grade metamorphism. Therefore, the basal contact of these Schneeberg rocks probably represents a Permian extensional fault or shear zone.

References:

Schmid et al. (2004) Eclogae geol. Helv., 97, 93-117.

Sölva et al. (2005) Tectonophysics, 401, 143-166.



Mon: 79
Topics: 13c) Tectonic Systems (TSK open session)

Exhumation of a metamorphic core complex: The journey from mid-crust to surface

Georg Löwe, Kamil Ustaszewski

Friedrich-Schiller-Universität Jena, Germany

Regional-scale extension in the internal Dinarides manifests by the occurrence of several metamorphic core complexes (MCC’s) located at the distal Adriatic passive margin and within the Sava Zone. The Sava Zone represents a suturing accretionary wedge juxtaposing Adriatic thrust sheets in a lower-plate position with European-derived units. In Oligo-Miocene times, the Sava Zone underwent substantial post-collisional extension, triggered by the opening of the Pannonian Basin in response to the NE-directed rollback-motion of the Carpathian slab.

Mt. Cer in western central Serbia represents one of such core complexes and is a key-feature allowing insights into regional-scale extension and associated magmatic and metamorphic processes. Cer MCC is part of the most distal Adriatic Jadar-Kopaonik composite thrust sheet and comprises a central I-Type granitoid of Eo-Oligocene age that was subsequently intruded by an S-Type granite. This multi-phase pluton was exhumed together with amphibolite-facies grade metapelites along a low-angle detachment with top-N transport at approx. 17 Ma as shown by Ar/Ar in-situ geochronology on deformed white mica.

We further used Al-in-hornblende (Hbl) geobarometry to constrain crystallizing pressures for the I-type granitoid. Results ranging from 5 to 6 kbar suggest a mid-crustal depth of intrusion of approx. 16 km while values obtained on Hbl from a lamprophyric dike intruding the I-type granitoid show a maximum at 2 kbar, corresponding to a depth of intrusion at roughly 5 km. Field observations confirm the lamprophyric dikes to be the youngest magmatic feature as they contain pegmatitic xenoliths of S-Type granitic composition.

Our results help to constrain exhumation in a spacio-temporal manner and contribute to a more detailed understanding of the interplay between magmatism and regional-scale extensional tectonics in the internal Dinarides.



Mon: 80
Topics: 13c) Tectonic Systems (TSK open session)

The Altmark Swell – sedimentary high or uplifted graben shoulder?

Alexander Malz

Landesamt für Geologie und Bergwesen Sachsen-Anhalt, Germany

The Altmark Swell in north-western Saxony-Anhalt forms a remarkable structure where sedimentary, facial and tectonic changes occurred during the Mesozoic evolution of the North German Basin. First, it evolved as a structural high in Late Palaeozoic to Early Triassic times, which is proved by several local to regional unconformities in the Buntsandstein Group. Later, i.e. during the Late Triassic, wide areas of the North German Basin area were affected by strong WNW-ESE-directed extension. This event is suspected to have initiated uplift and erosion on top of the Altmark Swell and thus led to the formation of a hiatus spanning the whole Middle to Late Triassic time period (approx. 40 Ma). Most often this is interpreted to have been associated with strong vertical movements in the mechanical basement (sub-salt strata) or was due to the formation of salt pillows.

In the framework of a large-scale 3D modelling campaign carried out at the geological surveys of Northern Germany we re-evaluated a dense network of interpreted reflection seismic sections and several hundreds of boreholes in the vicinity of the Altmark Swell. These data clearly confirm the sedimentological interpretations of earlier researchers and allows for the refinement of distribution outlines in the footwall of unconformities. Nevertheless the structural relationship of sedimentary basins, grabens and bordering faults as well as associated salt structures suggests that the Altmark Swell was rather influenced by huge sub-horizontal, decoupled movements (up to 5 km) along flat normal faults than with vertical, basement-involved faulting. We observed several large, flat faults linked with mechanically weak evaporates. These faults affected the Upper Buntsandstein Group to directly overlay the Zechstein salt. Large horizontal movements resulted in a particular structural configuration, several ramp-flat-ramp geometries and extensional duplexes. In the hanging wall of extensional detachments thick (1.5 km) Late Triassic strata was deposited while large salt pillows grew in the footwall of flat faults exposed on the Late Triassic surface.

In this contribution we present our observations and provide a tectonic-sedimentary model of the Altmark Swell, which helps to explain the distribution and extent of unconformities in relationship to fault and fold geometries observable over a distance of approximately 100 km along the western border of the Altmark Swell.



Mon: 81
Topics: 13c) Tectonic Systems (TSK open session)

Stress rotation due to discontinuities and material transitions

Karsten Reiter

TU Darmstadt, Germany

The in-situ stress state in the upper crust is an important issue for economic purposes and scientific questions as well. Several methods have been established in the last decades to indicate the present-day orientation of the maximum compressive horizontal stress (SHmax). It was assumed, that the SHmax orientation on a regional scale is governed by the same forces that drive plate motion. The SHmax orientation data, compiled by the World Stress Map (WSM) project, confirmed that for many regions in the world. Also due to the increasing amount of data, it is now possible to identify clearly several areas in the world, where stress orientation deviates strongly from the expected orientation due to plate boundary forces (first order stress sources), or the plate wide pattern. In some of this regions a gradual rotation of SHmax can be observed.

Several second and third order stress sources have been identified in the past that can explain the stress rotation. For example, these are lateral heterogeneities in the crust, such as density, petrophysical or petrothermal properties and discontinuities, like faults. Apparently, there is no study, which quantifies the potential amount of stress rotation depending on these second and third order stress sources in detail. For that reason, generic geomechanical numerical models have been set up, consisting of several sloping units, with variable elastic material properties such as Young’s modulus, Poisson ratio and density. An almost identical model geometry allows additionally to separate the units by contact surfaces allowing a slip along the faults, depending on a chosen friction coefficient.

The model results indicate, that a density contrast or variation of the Poisson’s ratio alone is only able to rotate the horizontal stress orientation sparsely. In contrast to that a lower or higher Young’s modulus as well as low friction on the faults allows significant stress rotations. Not only the area near a discontinuity or the material transition is affected by the stress rotation, whole blocks can be affected. This indicates that significant material contrasts and low friction discontinuities are able to generate significant stress rotation for larger areas in the crust.



Mon: 82
Topics: 13c) Tectonic Systems (TSK open session)

Salt pillow growth in the Bay of Mecklenburg, SW Baltic Sea: Timing and regional tectonic link

Niklas Ahlrichs1,2, Elisabeth Seidel2, Christian Hübscher2, Vera Noack1

1Federal Institute for Geosciences and Natural Resources (BGR), Berlin, Germany; 2University of Hamburg, Institute of Geophysics, Germany

We study salt pillow growth at the northeastern North German Basin margin (part of the Central European Basin System) by means of seismic imaging. New high-resolution gapless seismic sections from the BalTec project illuminate the stratigraphic and tectonic pattern of the subsurface from the base of the Zechstein salt to the seafloor. This allows a complete reconstruction and timing of salt movement from deposition to present day. We present key profiles across three adjacent salt pillows in the central area of the Bay of Mecklenburg (SW Baltic Sea). Stratigraphic correlation with onshore wells rests upon additional marine profiles as well as vintage land seismic surveys. We identify and compare phases of salt movement within the regional tectonic framework with emphasis on the nearby Glückstadt Graben and Tornquist Zone.

Salt pillow growth initiated in the Late Triassic with ongoing movement until the Jurassic. After a phase of cessation, salt movement rejuvenated in the Late Cretaceous and Tertiary. Contemporaneous tectonic activity in the Tornquist Zone allows a linkage of regional tectonics and salt movement. The rejuvenation of pillow growth in the Late Cretaceous correlates to the regional tectonic reorganization of the North German Basin and Tornquist Fan area and the change from an extensional to compressional setting alongside basinwide graben inversion and thrust faulting.



Mon: 83
Topics: 13c) Tectonic Systems (TSK open session)

Strain analysis of the Zervreila Orthogneiss of the northern Adula Nappe, eastern Switzerland, Central Alps

Burcu Tasdemir, Ruth Keppler, Nikolaus Froitzheim, Jacek Kossak-Glowczewski

IGM, Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany

The Adula Nappe of the Central Alps mainly comprises pre-Mesozoic basement rocks which were overprinted by eclogite fazies metamorphism during the Alpine cycle. The metamorphic peak conditions increase from 1.0-1.3 GPa/450-550°C in the north to 3.0 GPa/800°C in the south. The complex internal structure of the Adula Nappe is the consequence of intense deformation. According to Löw (1987) the northern Adula Nappe experienced at least four ductile alpine deformation events. The first Sorreda Phase (D1, 45-40 Ma) is attributed to isoclinal folding and thrust imbrication. The Zapport Phase (D2, 40-35 Ma) occurred during isothermal decompression (nappe emplacement) near peak conditions, leading to N-S orientated stretching lineations, mylonitic fabrics, isoclinal folding, and top-N shearing of the nappe. The Leis Phase (D3, 35-30 Ma) post-dates D2 and is still related to isothermal exhumation. It is characterized by coaxial deformation, WSW-ENE stretching lineations (orogen-parallel), and open to isoclinal folding. The formation of the Northern Steep Belt and N-vergent antiforms at the front of the Adula Nappe are attributed to the youngest Alpine deformation phase, the Carassino Phase (D4, 30-20 Ma). The sum of all these deformation phases is responsible for the complex present-day geometry of the Adula Nappe. However, the exhumation mechanism of the nappe is still in debate, since the models face kinematic problems through the absence of top-S shear sense indicators at the roof of the nappe.

In this study, we performed thin section analysis and applied the Fry method (center-to-center method) to determine deformation structures and the finite bulk strain of the northern part of the Adula Nappe, south of the Zervreila Lake. The method depends on competence difference of matrix and clasts. Thus, estimated finite strains are matrix strains at outcrop scale. Over thirteen Zervreila Orthogneiss outcrops within the study area were measured for finite strain.

Thin section analysis revealed a Sorreda Phase (D1) foliation defined by inclusions in feldspar grains. Fry analysis shows a high concentration in the flattening field of the Flinn diagram, and two samples plotting in the constrictional field. This slightly scattered pattern indicates an overprint of penetrative N-shearing Zapport structures (D2; mostly plane strain with some constrictional strain) by the younger coaxial Leis deformation phase (D3; flattening strain). The finite strain resulted from the addition of the effects of the two deformation phases.

References:

Löw, S. 1987. Beiträge zur Geologischen Karte der Schweiz N.F., 161, 1-84.



Mon: 84
Topics: 13c) Tectonic Systems (TSK open session)

On the indispensability of haptic sensations with hand specimens – a plea for integrating rock collections into structural geology and tectonics teaching in the digital era

Kamil Ustaszewski, Madeline Richter

Friedrich-Schiller Universität Jena, Germany

Experience from 5 years of teaching various structural geology and tectonics classes at both the Bachelor and Master level at the University Jena shows that the maintenance of an ample rock collection with hand specimens, which illustrate a large gamut of deformational fabrics, and its integration into ‘hands-on’ exercises forms a very welcome addition to traditional (and in the view of students sometimes soporific) classroom teaching. Vivid and convincing teaching necessitates the illustration of the numerous natural deformation processes with representative hand specimens rather than mere photographs of outcrops, samples or thin sections.

We started building a collection of rock specimens shortly after appointment of the first (senior) author at the Institute of Geosciences in Jena in 2013. Back then, the institute was hardly in possession of any hand specimens illustrating the broad gamut (as well as the aesthetics) of deformation fabrics. At present, the collection contains c. 150 specimens of samples, showing various types of tectonically induced strain fabrics (e.g. brittle vs. ductile fabrics, numerous types of foliations and lineations), igneous fabrics (magmatic flow textures, cumulate textures, intrusive contacts, migmatites) as well as examples of rock-fluid interaction (e.g. serpentinized peridotites or multiply veined carbonates). Specimens were mostly collected during student field trips and own research campaigns across Germany, the Alps and Carpathians, the Balkan peninsula and Taiwan.

The sample collection now portrays the rich spectrum of deformation fabrics acquired at both shallow-crustal conditions by dominantly frictionally controlled mechanisms (such as extension and shear fractures, cataclasites or dilational breccia) or during creep (crack-and-seal fabrics, various stylolites) as well as mid- to lower-crustal conditions by dominantly viscous mechanisms (numerous greenschist- to granulite-facies mylonites) or subordinately also frictional mechanisms (pseudotachylites).

Testimonies of our students suggest that studying traditional handouts during lectures along-side with hand specimens is a very welcome, more vivid addition to teaching, providing the students with much sought optic and haptic sensations that illustrate the large number of tectonic processes way better than field photographs (e.g. Outcropedia, outcropedia.tectask.org) or virtual 3D outcrops (e.g. eRock, www.e-rock.co.uk) can.

We hence conclude that the maintenance of a collection of hand specimens, displaying the spectrum of strain fabrics across a large range of both temperatures and strain rates is an indispensable (and well affordable) addition to traditional classroom teaching and not at all obsolete in the digital era.



Mon: 85
Topics: 13c) Tectonic Systems (TSK open session)

Extensional continental basins: Feedbacks between the tectonic and thermal history

Katharina Vogt1, Attila Balázs2, Taras Gerya3

1International Geothermal Centre, Bochum University of Applied Sciences, Bochum, Germany; 2Laboratory of Experimental Tectonics, Department of Sciences, Università degli Studi Roma Tre, Rome, Italy; 3Geophysical Fluid Dynamics Group, Institute of Geophysics, ETH, Zurich, Switzerland

Extension of continental lithosphere may result in a wide range of different crustal architectures, fault geometries, sediment patterns and thermal histories. These variations were shown to be strongly controlled by the rheological and thermal structure of the lithosphere, the kinematic history of the system, the existence of heterogeneities in the crust and/or mantle and surface processes. Understanding the geodynamic evolution of the system, and, in particular feedbacks between the tectonic and thermal history of the system has direct implications for the assessment of potential petroleum systems and geothermal applications. In order to better understand the time-dependent evolution of these key aspects, we conduct a series of numerical, thermo-mechanical models in 3D. These models are based on the thermo-mechanical code I3VIS, which solves the mass, momentum, and energy conservation equations for incompressible media. The code uses non-Newtonian viscoplastic rheologies to simulate flow and is specifically designed to study lithospheric extension. First results indicate the importance of rheological heterogeneities in the crust and/or mantle on the overall geometry and tectonic evolution of extensional continental basins. Reactivation of nappe contacts and fossil suture zone localizes deformation and results in asymmetric basins that exhibit along‐strike variability in terms of fault geometries, basement structures, subsidence, and thermal evolution.



Mon: 86
Topics: 13c) Tectonic Systems (TSK open session)

Using thermal springs to quantify deep fluid flow and its thermal footprint in the Alps

Elco Luijendijk1, Theis Winter1, Christoph von Hagke2, Grant Ferguson3

1Unviersity of Göttingen, Germany; 2RWTH Aachen, Germany; 3University of Saskatchewan, Canada

While several studies have shown that meteoric water can penetrate large parts of the crust and can strongly alter subsurface temperatures, the extent and thermal effects of deep fluid flow in mountain belts are still largely unknown. Here we present a newly compiled database of thermal springs in the Alps, which we use to quantify the extent of deep fluid flow and its thermal effects. The database contains temperature and discharge data for 450 springs and hydrochemistry and isotope data for 150 of the springs. We discuss the distribution of springs and the relation with tectonic and seismic activity of the Alps. We present a new heat and fluid flow model code and use this code to inversely model the depth of fluid conduits and faults that feed the springs. In addition, the model is used to quantify the thermal footprint of hot springs and the effects of fluid flow on low-temperature thermochronometers. The modeled maximum flow depth and temperatures are compared with independent estimates based on the hydrochemistry and stable isotope composition of spring water. The results provide one of the first large scale images of deep fluid and its thermal effects at the scale of an orogen.



Mon: 87
Topics: 10b) Detailed insights into geodynamic processes and geotechnical applications through neutron and synchrotron X-ray diffraction

Dynamic compression of baddeleyite in membran-driven diamond anvil cells as an analogue experiments for impact events

Falko Langenhorst1, Eric Adelhardt1, Ulrich Mansfeld1, Hanns-Peter Liermann2

1University of Jena, Germany; 2Deutsches Elektronen-Synchrotron (DESY)

Fast membrane-driven diamond anvil cell (mDAC) experiments were used to simulate the effects of shock compression in rock-forming minerals [1-3]. These experiments were carried out at synchrotons allowing to obtain time-resolved in-situ X-ray diffraction data of minerals during rapid compression and decompression. Despite the absence of shock waves in DAC experiments and their distinctly smaller compression rates compared to shock experiments, the mDAC technique yields known shock effects such as amorphization of quartz and feldspars [1,3] and dislocation glide in olivine [2]. Here, we performed dynamic mDAC experiments on baddeleyite (monoclinic ZrO2), an accessory mineral in planetary basalts, which is known to undergo various phase transformations. We focus on the nature and kinetics of pressure-induced phase transformations, which are much less constrained than the temperature-induced martensitic and displacive transitions.

Polycrstalline, 1 µm sized ZrO2 powder served as starting material in two mDAC experiments run up to 37 GPa and 64 GPa. This powder was dynamically compressed under non-hydrostatic conditions at a rate of 1 GPa/s. X-ray diffraction patterns were acquired at beamline P02.2 of PETRAIII, DESY Hamburg at 25.6 keV using a Perkin-Elmer fast flat panel detector. Powdered gold was used as an internal pressure standard. Recovered samples were investigated by transmission electron microscopy (TEM) to detect persistent structural modifications in baddeleyite.

In agreement with previous slow compression experiments [4,5], our synchroton X-ray diffraction experiments reveal the immediate transformation of monoclinic baddeleyite to the orthorhombic phases I, II, and III at 6, 22, and 40 GPa, respectively. On decompression these phases even persist without reversion to the baddeleyite structure. The lattice constants a, b, and c of the orthorhombic phases abruptly change at the transformation pressures, while the overall cell volume almost linearly increases with increasing pressure.

TEM inspection of recovered samples confirms the occurrence of nanocrystalline aggregates of the orthorhombic phases at ambient pressure. Individual nanocrystals are strongly strained but otherwise defect-free. These observations indicate the displacive nature of the pressure-induced phase transformations. The persistence of the orthorhombic phases at ambient pressure is attributed to internal strain in nanocrystalline aggregates.

[1] Carl E.-R. et al. (2017) Meteoritics & Planetary Science 52:1465-1474. [2] Langenhorst F. et al. (2017) 80th Annual Meeting of MetSoc: #1987. [3] Sims M. et al. (2019) Earth and Planetary Science Letters 507:166-174. [4] Leger J.M. et al. (1993) Phys. Rev. B 47:14075. [5] Bouvier et al. P. (2000) Phys. Rev. B 62: 8731.



Mon: 88
Topics: 10b) Detailed insights into geodynamic processes and geotechnical applications through neutron and synchrotron X-ray diffraction

EPSILON - the neutron time-of-flight strain/stress diffractometer and its sample environment for strain investigations in rocks

Christian Scheffzük1,2, Birgit I.R. Müller1, Roland Tremmel1, Badmaarag Altangerel2, Frank R. Schilling1

1Karlsruhe Institute of Technology, Institute of Applied Geosciences, Germany; 2Frank Laboratory of Neutron Physics, JINR Dubna, Russia

The investigation of uniaxial and triaxial stress states in mono- and polyphase geological samples is a key to a better understanding of the deformation behaviour of rocks. The neutron time-of-flight strain/stress diffractometer EPSILON at the pulsed neutron source IBR-2M is equipped with various sample environment techniques to enable in situ - deformation experiments as well as at axial and triaxial deformation conditions.

The neutron diffractometer is equipped with a detector system consisting of 9 detector units at a diffraction angle of 2θ=90°, so that 9 different sample directions can be investigated. Lattice spacings up to d= 5.3 Å are achievable, so that lower symmetrical crystal structures with large elementary cells can be investigated.

An axial pressure device enables σmax = 150 MPa using sample dimensions of Ø = 30 mm, l = 60 mm; the axial [σ1] and radial [σ3]-directions can be detected, simultaneously. The sample environment has been extended by a triaxial pressure device to generate the axial pressure σ1_max= 150 MPa, the confining pressure σ3_max= 70 MPa, and the pore pressure pp= 70 MPa, independently. This sample environment allows in situ determination of intracrystalline strain of porous polycrystalline materials.

We have developed and used this pressure device for the investigation of porous sandstone in order to generate the conditions in geological samples as they occur in upper crust reservoirs, namely in depth intervals of 3,000 to 5,000 m.



Mon: 89
Topics: 10b) Detailed insights into geodynamic processes and geotechnical applications through neutron and synchrotron X-ray diffraction

Pressure-induced crystallographic changes of dynamically compressed quartz by X-ray diffraction and electron microscopy

Christoph Otzen1, Hanns-Peter Liermann1, Falko Langenhorst2

1Deutsches Elektronen-Synchrotron DESY, Germany; 2Friedrich-Schiller-Universität Jena

Large asteroid impacts play a crucial role in the history of the Earth, traces of which can still be found in minerals today and provide important information about past impact events. Being robust evidence and barometers for impacts, the amorphization of tectosilicates is the most significant impact indicator. To constrain the pressure conditions for the occurrence of amorphization and observe the crystallographic changes in-situ, diamond anvil cell experiments are typically performed on powder samples for X-ray diffraction. Powders, having typical grain sizes in the micron to submicron range, however, are inadequate to analyze how amorphization is affected by the orientation of the crystal with respect to the direction of load. Furthermore, the small particle sizes are unrepresentative of natural target material which consists of grain sizes in the millimeter range.

In the present work, we have carried out dynamic compression experiments on various orientations of quartz single crystals at the Extreme Conditions Beamline at PETRA III, DESY, Hamburg, Germany. Aiming at creating the dynamic pressure conditions that can be found in natural impacts, we use membrane-driven diamond-anvil cells to compress the samples uniaxially and rapidly to high pressures. Using transmission electron microscopy, we analyze the pressure-induced crystallographic changes of the recovered single crystals in detail. Our research provides insights into the mechanisms of pressure-induced amorphization in quartz.



Mon: 90
Topics: 10b) Detailed insights into geodynamic processes and geotechnical applications through neutron and synchrotron X-ray diffraction

Synchrotron diffraction as a tool for the texture analysis of mid-ocean ridge serpentinites

Rebecca Kuehn1, Michael Stipp1, Bernd Leiss2, Jan Behrmann3

1Martin-Luther-University Halle, Department of Geodynamics, Halle (Saale), Germany; 2Geoscience Center of the Georg-August-Universität Göttingen, Department of Structural Geology and Geodynamics, Göttingen, Germany; 3GEOMAR Helmholtz Centre for Ocean Research Kiel, Marine Geodynamics, Kiel, Germany

Oceanic serpentinites comprise to a great extent the serpentine polymorphs lizardite and chrysotile. Analysis of their crystallographic preferred orientation (texture) is challenging due to the fibrous crystal habit of chrysotile. More conventional methods such as electron backscatter or neutron diffraction are inapplicable, as the first requires polished surfaces that cannot be produced, while for the second neutrons are absorbed by the hydrogen within the serpentine crystal lattice, respectively. We therefore used hard X-ray synchrotron diffraction for unpolished sample cylinders with a diameter of up to 20 mm, which is also suitable for samples containing hydrous minerals.

Measurements were conducted at the European Synchrotron Radiation Facility in Grenoble, France at beamline ID22. As beam size was limited to 1 mm, we measured several slices of the full sample cylinder to improve grain statistics. A suite of serpentinite samples from the Atlantis Massif oceanic core complex, located on the mid-Atlantic ridge at 30° N, was studied. They were cored during International Ocean Discovery Program Expedition 357.

Samples are highly altered ultramafics, containing lizardite and chrysotile, as well as magnetite and further minor minerals. The textures and microstructures vary from weakly foliated bastite-rich to strongly foliated bastite-free mesh structures. Samples with less or no bastite clasts have intense foliations defined by the orientation of the serpentinizing microfractures. Serpentine texture in bastite-rich samples is dominated by the bastites, while in bastite-poor samples the texture seems to be controlled by the serpentinizing microfractures. The variations could depict differences in strain, in primary composition or fabrics inherited from the peridotite.

We show that synchrotron diffraction can be successfully used to determine the textures of oceanic serpentinites. This overcomes the severe limitations posed by more conventional methods, and opens the possibility of quantitative assessment of physical properties of hydrated oceanic Earth's mantle. Even though the texture in the samples originates from different microfabrics, it may lead to enhanced anisotropic physical properties.



 
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