Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany: reconstruction of an intra-continental supereruption

Marcel Hübner,Alexander Repstock,Franziska Heuer,Bernhard Schulz,Christoph Breitkreuz,Anna Pietranik,Manuel Lapp

doi:10.1007/s00531-021-02053-5

Marcel Hübner, Alexander Repstock + Show 5 more

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https://doi.org/10.1007/s00531-021-02053-5

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Abstract

Extensional tectonics in the Late Paleozoic Central Europe was accompanied by rift magmatism that triggered voluminous intracontinental caldera-forming eruptions. Among these, the Lower Permian Rochlitz Volcanic System (RVS) in the North Saxon Volcanic Complex (Eastern Germany, Saxony) represents a supereruption (VEI 8, estimated volume of 1056 km3) of monotonous rhyolites followed by monotonous intermediates. Mapping, petrography, whole-rock geochemistry along with mineral chemistry and oxygen isotopes in zircon display its complex eruption history and magma evolution. Crystal-rich (> 35 vol%), rhyolitic Rochlitz-α Ignimbrite with strong to moderate welding compaction erupted in the climactic stage after reheating of the magma by basaltic injections. Due to magma mixing, low-volume trachydacitic-to-rhyolitic Rochlitz-β Ignimbrite succeeded, characterized by high Ti and Zr-values and zircon with mantle δ18O. Randomly oriented, sub-horizontally bedded fiamme, and NW–SE striking subvolcanic bodies and faults suggest pyroclastic fountaining along NW–SE-oriented fissures as the dominant eruption style. Intrusion of the Leisnig and the Grimma Laccoliths caused resurgence of the Rochlitz caldera forming several peripheral subbasins. In the post-climactic stage, these were filled with lava complexes, ignimbrites and alluvial to lacustrine sediments. Significant Nb and Ta anomalies and high Nb/Ta ratios (11.8–17.9) display a high degree of crustal contamination for the melts of the RVS. Based on homogenous petrographic and geochemical composition along with a narrow range of δ18O in zircon Rochlitz-α Ignimbrite were classified as monotonous rhyolites. For the Rochlitz-β Ignimbrites, underplating and mixing with basic melts are indicated by Mg-rich annite–siderophyllite and δ18O < 6.0 in zircon. The wide spectrum of δ18O on zircon suggests an incomplete mixing process during the formation of monotonous intermediates in the RVS.

Highlights

Eruptions forming voluminous crystal-rich ignimbrites are often related to reheating of crystal mush in the magma reservoir; underplating/injection of basic melts causes magma mingling, mixing and homogenization (Smith 1979; Bachmann et al 2002; Bachmann and Bergantz 2004; Christiansen 2005; Folkes et al 2011)
Outcrops and drillings reveal that the Rochlitz Volcanic System (RVS) is bordered by subvertical faults in the N, NE and SW, which are assumed to have acted as volcanotectonic normal faults during caldera subsidence (Fig. 2)
A small block of the Variscan basement was uplifted in the central RVS forming a horst like structure (Fig. 2)

Summary

Introduction

Eruptions forming voluminous crystal-rich ignimbrites are often related to reheating of crystal mush in the magma reservoir; underplating/injection of basic melts causes magma mingling, mixing and homogenization (Smith 1979; Bachmann et al 2002; Bachmann and Bergantz 2004; Christiansen 2005; Folkes et al 2011) This may result in the formation of monotonous intermediates known from many subduction-related settings (Hildreth 1981; Huber et al 2012; Bachmann and Huber 2016; Kaiser et al 2017). Further examples are the Halle Volcanic Complex in central Germany (Breitkreuz et al 2018; Fig. 1) and the Intra-Sudetic and North Sudetic Basins in Poland and Czech Republic (Awdankiewicz 1999)

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