Crustal xenoliths from Eifel volcanoes: constraints on continental crustal structures and timing of Quaternary volcanism

• Applicant: Professor Dr. Mario Trieloff, since 1/2023
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450662246

The Eifel is one of the world’s best-investigated continental intraplate volcanic fields. Magma ascent from the upper mantle through the continental crust to the surface, however, remains incompletely understood for these systems. Open questions also exist regarding the eruptive recurrence in the Eifel during its Quaternary activity. Mafic magmas en route to the surface often entrain xenolithic fragments of continental crustal rocks, which can yield unique insights into concealed crustal structures in volcanically active regions such as the Eifel. Crustal xenoliths provide tangible evidence of the chemical and mineralogical composition of crustal rocks, and they record when the crust was consolidated and last thermally and structurally overprinted. Pre- and syn-eruptive heating of xenoliths causes diffusion and resetting of radioactive decay systems. This also permits dating of processes near the time of eruption. Crustal xenoliths from maar volcanoes and scoria cones in the West Eifel and East Eifel volcanic fields comprise a spectrum of diverse sedimentary and metamorphic rocks, which allow reconstruction of a detailed crustal profile including basement and cover rocks that make up the Rhenish Massif. Gneissic and granulitic rocks from the Variscan mid- and lower crust are of particular interest as these are regionally not exposed. This project aims at investigating zircon and other accessory minerals to (1) constrain the magmatic and metamorphic pre-history of crustal rocks in the Eifel; and (2) quantify eruption ages and processes of pyrometamorphic overprint of the same xenoliths during Quaternary volcanism. For this, U-Pb dating of zircon will yield robust crystallization ages, whereas the conditions of zircon crystallization can be constrained by trace element and isotopic data. Eruption ages will be determined by (U-Th)/He zircon geochronology. Relative timescales of pre- and syneruptive heating will be further quantified through diffusion modelling of Li in zircon, which also will aid in the interpretation of (U-Th)/He dates for zircon from xenoliths. The proposed research will contribute to deciphering deep crustal structures in the Rhenish Massif, and constrain the Quaternary volcanic evolution of the Eifel in order to re-assess the volcanic hazard potential of this potentially active volcanic area. Combined radiometric and diffusion-based chronometry is an important improvement of the (U-Th)/He dating method applied to xenoliths, with far-reaching applications for the dating of mafic eruptions.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Axel Karl Schmitt, Ph.D., until 12/2022