Insights into magmatic evolution in the southern Central European Volcanic Province: Petrology and Geochronology

Based on U-Pb geochronology, strongly SiO2-undersaturated foidites and melilitites in the southern Central European Volcanic Province (SW Germany, E France) were shown to have formed during two distinct periods in different regions. An Upper Cretaceous to Lower Eocene group (~72–47 Ma) is characterized by melilite-free nephelinites, nepheline basanites, and haüynites, whereas an Oligocene to Miocene group (27–9 Ma) is represented by olivine melilitites and melilite-bearing nephelinites. Both rock series were generated by extremely low degrees of partial melting of the metasomatically overprinted sub-lithospheric mantle, but exhibit a number of distinct mineralogical, mineral chemical, and whole-rock geochemical features. However, thermodynamic modelling did not reveal significant differences for melt temperature, oxygen fugacity, and silica activity. Accordingly, the foiditic and melilititic melts formed at temperatures of 1100–1350 °C and their polybaric crystallization started at ~14 kbar. The silica activities vary for both age cohorts between ~0.4 and 0.9 with a ΔFMQ of +1 to +4. Thus, it is likely that the differences between the rock series reflect a temporally and spatially heterogeneous sub-lithospheric mantle source beneath central Europe and are coupled to different depths of melt formation, various initial melt compositions, and/or different degrees of partial melting. Besides, an influence of crustal contamination and fractionation cannot be completely excluded. Magmatism in both periods is associated with asthenospheric doming and surface uplift causing erosion and isostatic compensation in the Alpine foreland. These processes indicate decompression and are interrupted by a period of subsidence resulting in a ~20 Myr volcanic hiatus.