1:30pm - 1:45pm
Recurrent continent-scale hiatus surfaces in Europe and links to upper mantle flow
Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München
Mantle convection is a fundamental driving force for the tectonic activity of our planet. It is commonly perceived that mantle convection is difficult to constrain directly. Its processes, however, affect the surface of the Earth and leave an imprint in the geological record. One response to topographic changes driven by mantle convection is the development of unconformities in the geological record (i.e. the absence of a stratigraphic layer), due to non-deposition or erosion. Modern geological maps allow systematic mapping of such unconformable surfaces at the continental scale.
Here we report our recently published work on the extraction of conformable and unconformable contacts (continent-scale hiatus mapping) in geological series across America, Europe, Africa, and Australia, from the Upper Jurassic onward. We find significant differences in the spatial extend of hiatus patterns across and between continents at geological series, ten to a few tens of Million years (Myrs). This is smaller than the mantle transit time, which, as the timescale of convection, is about 100–200 Myrs, implying that different timescales for convection and topography in convective support must be an integral component of time-dependent geodynamic Earth models. For the Cenozoic sedimentary cover of Europe the maps show a large hiatal surface of the Paleocene. This surface precedes the arrival of the Iceland plume and the change in motion of the North Atlantic ridge in the early Eocene.
Our results call for intensified collaboration between geodynamicists and geologists to improve our understanding of interregional-scale geologic events.
1:45pm - 2:00pm
Novel Mantle flow retrodictions reveal preferential material flow in the sublithospheric European mantle
1Ludwig-Maximilians Universitaet, Germany; 2Australian National University
The Cenozoic tectonic evolution of Northern Europe involves a number of events that are difficult to reconcile with an intra-plate setting, including magmatic events and topographic changes that are located far from plate boundaries. It is entirely plausible to relate these events to sublithospheric processes in a vigorously convecting mantle. However, traditional mantle convection models are difficult to link to the spatiotemporal constraints provided by geologic archives, because their output invariably depends on the assumptions of poorly known and arbitrary initial conditions. Here we explore a new class of time-dependent global geodynamic Earth models, known as retrodictions, which are based on inverse approach to
reconstruct past mantle flow and structure. Our high resolution, compressible, global mantle ﬂow retrodictions involve more than 670 million finite elements.
Going back 50 million years ago they reveal a preferential flow direction in the sub-European mantle related to material influx from the North Atlantic realm. The retrodictions allow us to track material back in time from any given sampling location, making them potentially useful, for example, to geochemical studies. Our results call for improved estimates on non-isostatic vertical motion of the Earth’s surface – provided, for instance, by basin analysis, seismic stratigraphy, landform studies, thermochronological data, or the sedimentation record – to constrain the recent mantle ﬂow history beneath northern Europe and suggest that mantle ﬂow retrodictions may yield powerful synergies across diﬀerent Earth sciences disciplines.
2:00pm - 2:15pm
Volcanites of MORB and WPB character in the evaporitic Permian Haselgebirge Formation (Eastern Alps, Austria) and possible tectonic implications
1University Salzburg, Austria; 2Technical University München, Germany
The evaporitic Haselgebirge Formation hosts in many places small occurrences of basaltic rocks. The geochemistry of these basalts can potentially provide information about the tectonic setting of the Haselgebirge Formation and the evolution of the Meliata ocean, respectively. XRD analysis and thin sections give hints to the original geochemistry, however the basalts altered significantly in contact with brines. Therefore, we present here 70 new XRF analyses of these basaltic rocks from various localities (Pfennigwiese, Annaberg, Wienern, Hallstatt, Moosegg, Lammertal) and compare the results with previous data from local studies (Gruber et al., 1991; Kirchner 1979; Kirchner 1980a; Kirchner 1980b; Kralik et al, 1984; Leitner et al., 2017; Schorn et al., 2013; Ziegler, 2014; Zirkl, 1957). Based on the concentrations of immobile trace elements (Zr, Nb, Y, Ti), a predominance of MORB-like compositions is observed for the Lower Austrian occurrences and for the locality Wienern (Grundlsee). On contrast, basalts from the localities Lammertal, Moosegg and Hallstatt have predominantly within-plate-type compositions. Both groups plot for the most part in the plume source field after Condie (2003). We discuss a striking regional (east-west) difference of basalt types in terms of existing palinspastic models for the Haselgebirge formation (Leitner et al., 2017; Stampfli & Borel, 2002; McCann et al., 2006).
2:15pm - 2:30pm
The Werra-Fulda mining district, underground extension of the CEVP-alkaline magmatic province – New insights in the magmatic evolution and its interaction with evaporitic deposits.
1K+S Aktiengesellschaft, Kassel, Germany; 2Institute of Earth Sciences, Heidelberg University, Germany; 3Sedimentology & Environmental Geology, Geoscience Center, University of Göttingen, Germany
The Werra-Fulda mining district located in Central Germany hosts a world-class deposit of sulfate bearing potash salts. The Permian (Zechstein, ca. 255 Ma) evaporite sequence was intruded by mafic melts in the Neogene resulting in magmatic dykes as well as sill structures frequently observed in the subsurface mining galleries. Furthermore, volcanic rocks intersect the overlaying strata (mainly Buntsandstein and Muschelkalk) at localized spots forming distinct mountains.
In this study, samples from subsurface mafic dykes and surface volcanic rocks were intensively documented, sampled, and analyzed for their major, minor, and trace element composition. The geochemical analyses allow the characterization of the rocks that show compositions typical for within plate basanites and nephelinites with minor occurrences of phonolitic dykes. Results of the study also indicate the interaction of magma with adjacent potash salts and partly alteration of potassium and sodium concentration.
Two distinct trends in magmatic composition are revealed suggesting at least two sources for the magmatic feeder system in the local area. The geochemical results are compared to published data of the area and nearby volcanic complexes in the Rhön, Vogelsberg, Westerwald, and Siebengebirge. Additionally, we tested the fission-track and (U-Th-Sm)/He dating technique by using apatite from more than 100 magmatic rock samples. Preliminary, results provide two magmatic events: one at about 21 Ma and the other at about 13 Ma. Both events are accompanied by localized tectonic reactivation.
2:30pm - 2:45pm
Mesozoic to Cenozoic exhumation history of the Odenwald and Heidelberg, Germany
1Institute of Earth Sciences, Heidelberg University, Germany; 2Sedimentology & Environmental Geology, Geoscience Center, University of Göttingen; 3Department of Geological Sciences, University of Texas, Austin,
In Germany, the first apatite fission-track study was performed in the Odenwald (Wagner 1968) with the results of Mesozoic apatite fission-track ages. The presentation will re-examine the Mesozoic-Cenozoic exhumation history of the Odenwald and Heidelberg area with new thermochronological data. The Odenwald as part of the Mid-German Crystalline Zone is characterized by outcrops of the Variscan basement and overlain Mesozoic and Cenozoic strata. Towards the West, the Variscan Basement is bound by the Upper Rhine Graben basin and towards the East by the Mesozoic and Cenozoic cover. Variscan basement rocks, Mesozoic, and Oligocene sandstones have been studied by apatite fission-track and apatite (U-Th-Sm)/He thermochronology.
Apatite fission-track ages range between 70.4±3.8 Ma and 116.7±5.2 Ma and apatite (U-Th-Sm)/He ages between 66.4 ± 4.0 Ma and 121.3 ± 16.7 Ma. Apatite of the Oligocene sandstone deposit near Heppenheim revealed a central fission-track age of 49.4±3.6 Ma. The thermochronological data show a differentiated age distribution with cooling ages getting younger from north to south. Consequently, we assume that exhumation of the rocks in the northern part set in earlier a took place slower than in the southern part of the Odenwald. Numerical modelling using the software code HeFtyimplies either a high Cretaceous heat flow or a maximum of up to 2830 meters of Mesozoic sedimentary rocks that could have covered the Odenwald crystalline basement during the Cretaceous. The modelled t-T-evolution hints at two major phases of exhumation, one in the Cretaceous and one in the Neogene.