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

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.

Large-Volume Permian Felsic Volcanism in the Tisza Mega-Unit (East-Central Europe): Evidence from Mineralogy, Petrology, Geochemistry, And Geochronology

“…As discussed before, the Highis ¸ granitoid and subvolcanic samples, showing an apparently primary magmatic composition (Fig. 12), suffered from a penetrative alteration effect of halogen-rich (Ishikawa et al, 1976) vs. Carbonate-Chlorite-Pyrite Index (Gifkins et al, 2005) plot (modified after Shanks III and Thurston, 2012;Hübner et al, 2021) focusing on the postmagmatic alterations of the studied Permian volcanic rocks as well as the Highis ¸ granitoids (Szemerédi et al, 2021). fluids shortly after the Middle Permian emplacement (Bonin and Tatu, 2016;Szemerédi et al, 2021).…”

“…In general, the mineralogical and chemical compositions of pyroclastic rocks such as welded ignimbrites can be modified by vapor-phase reactions and subsequent diagenetic processes (e.g., silicification, Kand/or Na-metasomatism). Furthermore, many ancient volcanic rocks were affected by various types and degrees of alterations, including recrystallization, hydrothermal overprint, and metamorphism (see, e.g., McPhie et al, 1993;Gifkins et al, 2005;Hübner et al, 2021). Previous studies (Bonin and Tatu, 2016;Nicolae et al, 2014;Szemerédi et al, 2020aSzemerédi et al, , 2021Tatu, 1998) revealed that the Permian felsic volcanic and plutonic rocks in the Tisza MU were also influenced by various postmagmatic alterations, including multiple hydrothermal effects and, locally, deformations (Alpine metamorphism, Miocene tectonics).…”

“…12. (a) Na 2 O/Al 2 O 3 vs. K 2 O/Al 2 O 3 and (b) Na 2 O/K 2 O vs. SiO 2 /Al 2 O 3 diagrams (Garrels and Mackenzie, 1971), and (c) Alteration index(Ishikawa et al, 1976) vs. Carbonate-Chlorite-Pyrite Index(Gifkins et al, 2005) plot (modified afterShanks III and Thurston, 2012;Hübner et al, 2021) focusing on the postmagmatic alterations of the studied Permian volcanic rocks as well as the Highis ¸ granitoids(Szemerédi et al, 2021).…”

Diverse magma evolution recorded in trace element composition of zircon from Permo-Carboniferous rhyolites (NE German Basin, NW Polish Basin)

“…On the other hand, extensive and thick sheets of welded ignimbrite with high explosivity centres are found on the eastern part of the Variscan Belt in Europe (e.g. calderas of the North Saxon Volcanic Center, Hübner et al 2021;Repstock et al 2018; or the Altenberg-Teplice, Casas-García et al 2019Fig. 1); whereas a wide range of possible morphological volcanic forms occurs within the voluminous magmatism of the Central European Variscan foreland surrounded by the (SPB) Southern Permian Basin (e.g.…”

A New Water-Based 87Sr/86Sr Isoscape Map of Central and NE Germany, with Special Emphasis on Mountainous Regions

“…The small sub-catchment of the Freiberger Mulde (Eastern Erzgebirge) has a very diverse lithology where Paleozoic gneisses and phyllites alternate with granites, volcanic dykes, but also with some Cretaceous sediments. In addition, numerous hydrothermal and mineral deposits occur in this region (Hoth et al 1995;Rohde 2014;Fig. 2a).…”