Xenoliths transported to the surface by ascending magmas are crucial to decipher the structure and composition of the Earth’s crust and provide valuable insights into melt formation and magma storage conditions. This cross-crustal sampling is of particular importance in regions where no basement outcrops exist, such as the Eifel, Germany. Crustal xenoliths containing zircon are suitable targets for U/Pb geochronology to quantify the timing of intra-crustal magmatic and metamorphic events.
The Quaternary Eifel volcanic field consist of >300 volcanoes including maars, scoria cones and tuff rings. Precise eruption ages for these are rare and often inconsistent between the different methods. A promising approach to determine accurate eruption ages is to apply (U-Th)/He geochronology to zircon extracted from partially re-melted crustal xenoliths embedded in pyroclastic material.
So far, we collected >200 xenoliths from >35 volcanoes in the West- and East Eifel. We observe significant differences in xenolith abundance between the volcanic centers and a variety of xenolith types, including magmatic and metamorphic rocks with varying degrees of pyrometamorphic overprinting. Zircon crystallization ages range from ca. 2000 to 280 Ma, clustering around Variscan and Caledonian ages. Remarkably, the youngest U/Pb ages indicate post-Variscan plutonic magmatism reaching to the Permian, which has not yet been reported for this area.
Preliminary (U-Th)/He zircon eruption ages acquired for the Meerfeld and Gemünden Maar confirm the feasibility of the method. Future work on xenolith samples from additional centers will generate a comprehensive dataset of eruption ages to unravel the spatiotemporal evolution of the Eifel volcanic field.