Hübner, Marcel
[VerfasserIn];
Breitkreuz, Christoph
[VerfasserIn];
Repstock, Alexander
[VerfasserIn];
Schulz, Bernhard
[VerfasserIn];
Pietranik, Anna
[VerfasserIn];
Lapp, Manuel
[VerfasserIn];
Heuer, Franziska
[VerfasserIn]
Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany
: reconstruction of an intra‑continental supereruption
Beschreibung:
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 km 3 ) 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 δ18 O. 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 δ 18 O 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 δ18 O < 6.0 in zircon. The wide spectrum of δ 18 O on zircon suggests an incomplete mixing process during the formation of monotonous intermediates in the RVS. Keywords: Monotonous rhyolites · Monotonous intermediates · Magma mixing · Ti-in-biotite thermobarometer · δ18O in zircon · VEI 8 fissure eruption