Two distinct age groups of melilitites, foidites, and basanites from the southern Central European Volcanic Province reflect lithospheric heterogeneity

Abstract

Petrographic observations and in situ U–Pb ages of melilitites, foidites, basanites, phonolites, and trachytes from the southern part of the Central European Volcanic Province (CEVP) and related plutonic inclusions therein reveal two distinct age groups separated by a gap of ~ 20 Myr. A late Cretaceous to early Eocene group (~ 73–47 Ma; Taunus, Lower Main plain, Odenwald and Kraichgau area, Bonndorfer Graben and Freiburger Bucht area, Vosges and Pfälzerwald) is characterized by nephelinites and basanites mostly devoid of melilite and perovskite, and by rare haüynites, and trachytes. In contrast, a late Oligocene to late Miocene group (~ 27–9 Ma; Lorraine, southern Upper Rhine Graben, Urach, Hegau area) is dominated by melilitites, melilite-bearing nephelinites (both carrying perovskite), and phonolites. Both magmatic episodes are related to domal topographic uplift, erosion, and formation of major angular unconformities in the Upper Rhine Graben, suggesting an association with dynamic topography interrupted by phases of subsidence (or abatements of uplift). The investigated rocks in the southern CEVP (south of a line Eifel–Vogelsberg–Rhön–Heldburg), except for the Kaiserstuhl volcanic complex, mostly comprise small and isolated occurrences or monogenetic volcanic fields, whereas the northern CEVP is dominated by large volcanic complexes and dyke swarms, which are mostly SiO2-saturated to weakly SiO2-undersaturated. In the northern CEVP, evidence of spatially varying but recurrent volcanic activity exists since the Eocene, lacking the distinct 20 Myr gap as documented from the southern CEVP. While the temporal and spatial distribution of volcanism are a result of the Cretaceous to Miocene tectonic evolution in Central Europe, further studies are needed to explain the petrographic differences between the two age groups in the south.

The Muschelkalk aquifer of the Molasse basin in SW-Germany: implications on the origin and development of highly saline lithium-rich brines in calcareous hydrothermal reservoirs

“…The early Miocene Upper Marine Molasse, deposited during Burdigalian transgression, consists of shales and glauconite sands. The fluviatile sediments of the middle-to-late Miocene Upper Freshwater Molasse intercalate with the 14-9 Ma volcanic and volcaniclastic rocks in the Hegau area (Schreiner 1992;Binder et al 2022). Middle-to-early Miocene regional uplift and erosion affected SW-Germany and consequently parts of the Molasse basin fill have been eroded (Bachmann et al 1987;Bertleff et al 1988;Geyer and Gwinner 2011;Stober 2014;Hoffmann, 2017;Schreiner 1992).…”