Lavas from the Quaternary East and West Eifel volcanic fields in western Germany are among the youngest volcanic products of the Central European Volcanic Province (CEVP). In a comprehensive approach, we report Sr-Nd-Pb-Os isotope as well as major and trace element data for 59 samples covering Quaternary Eifel volcanism. In accord with previous studies, all lavas are SiO₂-undersaturated including primitive basanites, melilitites, and nephelinites as well as phonolites. In the West Eifel Field (WEVF), Sr–Nd–Pb compositions of the younger ONB-suite lavas are similar to FOZO or the EAR. Conversely, older (700 to 80 ka) F-suite lavas in the WEVF and from the entire East Eifel Field (EEVF) tap a more enriched mantle component, as illustrated by more radiogenic Sr isotope compositions and variable Pb isotope compositions. Radiogenic isotope compositions of F-suite and EEVF lavas require the admixture of melts from lithospheric mantle sources. Elevated Nb/Ta and Lu/Hf in combination with variable Os isotope compositions indicate residual carbonated eclogite components as a possible source of CO₂ in the lavas. The presence of a mantle plume can neither be confirmed nor excluded based on geochemical data alone. However, the absence of W isotope anomalies together with only moderately elevated He isotope compositions argue against a deep-rooted plume beneath the Eifel volcanic fields. Collectively, plume-like melt pulses that partially tap carbonated eclogite domains and interact to variable extents with the lithospheric mantle provide a viable model for the compositional spread of volcanism in the Eifel and elsewhere in the CEVP.

The eruption history and geochemistry of the Laacher See tephra 12.9 ka ago are well-documented. This study is the first to investigate the magnetic properties of the approximately 55 m thick tephra deposits south of the vent. The goal is to establish a relationship between magnetic properties, magma fractionation processes, and emplacement conditions. Magnetic susceptibility, its field- and temperature-dependence, and natural remanent magnetization were measured, and the petrography of the opaque phases was studied. Magnetic susceptibility increases significantly with stratigraphic height, starting from very low values in the lowest deposits. This trend is also seen in remanent and total magnetization, due to an increase in the number and size of titanomagnetite grains in ash and pumice lapilli. The increase in crystal content is attributed to the highly zoned magma reservoir of the Laacher See volcano, resulting from fractional crystallization. Post-eruption, the tephra deposits represent the inverse magma column, with less fractionated crystals at the top. Field- dependence measurements of magnetic susceptibility reveal three zones with slight field dependence (up to 10 %) and a zone without field dependence in between. These four zones are also observed in temperature-dependent magnetic susceptibility. Heating curves typically show Curie temperatures between 480 °C and 530 °C, while cooling curves show significantly lower Curie temperatures (up to 200 °C), likely due to cation ordering effects. Total magnetization values provide new insights into the magnetic anomaly field in the Laacher See region, suggesting previous models overestimated magnetization by up to two orders of magnitude at depth.

Silicate melts play a key role in Earth’s evolution, influencing differentiation and planetary cooling. Understanding their formation and properties in the lower mantle is essential but remains directly directly inaccessible.

This work investigates structural changes in the coordination environment of strontium and yttrium in silicate glasses at high pressure. Laser-heated DAC experiments with X-ray absorption spectroscopy were performed at ID24, ESRF. Spectra were obtained for two simplified basaltic glass compositions of in the systems Albite-Diopside and Anorthite-Diopside. In the AbDi-glass, part of Si was replaced by Ge [1]. Both contained Sr and Y at various levels.

EXAFS analysis showed a two-stage pressure response for both elements: initial bond lengthening and coordination increase up to ~20 GPa, then bond shortening and densification. In both glasses, the change in the trend of the Y–-O and Sr–-O distances at ~20 GPa, coincides with the stabilization of higher coordination states (CN = 7 for Y, CN = 8 for Sr). Bond valence analysis of the determined bond lengths confirms the coordination transitions upon compression. The results are consistent with molecular dynamics simulations for Ca and Mg in basaltic melts [2] and experimental high-P data for Sr in aluminosilicate glass [1]. These coordination changes may affect crystal–melt partitioning at depth [3], e.g., during magma ocean crystallization or near the core–mantle boundary.

References:
[1] Krstulović et al. (2021), Chem. Geol. 560, 119980, https://doi.org/10.1016/j.chemgeo.2020.119980
[2] Karki et al. (2018), in Magmas Under Pressure, Elsevier, https://doi.org/10.1016/B978-0-12-811301-1.00016-2
[3] Ozawa et al. (2024), Sci. Adv. 10, eadp0021, https://doi.org/10.1126/sciadv.adp002

Hot spot volcanism may reflect both contributions from sublithospheric and lithospheric mantle sources. In addition to lithophile radiogenic isotopes, Re-Os isotopic data may aid in understanding the contributions from different sources. The Galápagos archipelago is the manifestation of a long-lived mantle plume. Its source reservoirs are well characterized in terms of lithophile radiogenic isotopes, major and trace elements. A distinctive feature of the Galápagos mantle source is the presence of a strongly incompatible element-depleted component that mixes in three directions with an EM1-like plume signature and a HIMU-like endmember expressed in lavas from Floreana. However, Re-Os-systematics of Galápagos, are limited by very few basalt samples. In this contribution, we present highly siderophile element (HSE) and Re-Os isotopic data of 19 ultramafic xenoliths and 2 basalts from Isla Floreana in the southern Galápagos Archipelago.

HSE patterns in the xenoliths reveal two distinct groups: some exhibit high Pd/Ir and Pt/Ir, similar to ultramafic cumulates from ophiolites, whereas other xenoliths display low Pd/Ir and Pt/Ir, consistent with typical mantle xenoliths. Measured ¹⁸⁷Os/¹⁸⁸Os vary between 0.1265 and 0.1372 and overlap with data on basalts from Isla Floreana (0.130 to 0.140) and Isla Fernandina (0.132) (Gibson et al. 2016, EPSL 449, 345-359), where the plume centre is currently located. Cumulate xenoliths and their 187/188 Os mostly reflect the slightly suprachondritic values of the lavas, while other xenoliths with lower 187/188 Os are of lithospheric origin.

The Deccan Volcanic Province (DVP) represents one of Earth’s most voluminous continental flood basalt events, erupting an estimated 1.3 × 10⁶ km³ between ~66.3 and 65.5 Ma (Jay and Widdowson, 2008; Schoene et al., 2019). This study focuses on the Thakurvadi Formation (erupted ~66.3–66.1 Ma), and the overlying giant plagioclase basalt units, to understand magma evolution, crustal assimilation, and volatile element behaviour during eruption. Field mapping and trace element geochemistry of the Thakurvadi formation reveal systematic Cu/Ag variability that correlates with proxies for mantle heterogeneity. To test whether this variability reflects primary mantle signatures or is attributable crustal processes (assimilation, fractionation, degassing), we will integrate whole rock radiogenic isotope analyses (Sr, Nd, Pb, W). Preliminary Cu/Ag trends for my samples suggest links with radiogenic isotope signatures observed by Pakulla et al., (2023), potentially indicating ancient mantle source characteristics. By combining new isotopic data for my samples with the existing trace element and isotope datasets by Pakulla et al. (2023), we will be able to establish parental melt compositions, understand the extent of crustal contamination, and assess toxic element release (e.g., As, Se) during magma ascent and weathering. The resulting comprehensive geochemical framework will advance our understanding of DVP eruption dynamics, inform models of Large Igneous Province formation, and, by understanding the role of toxic elements, potentially contribute to understanding the environmental impacts of early Deccan volcanism on the Late Cretaceous environment.