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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. [ABSTRACT FROM AUTHOR]

Abstract: To discriminate possible anthropogenic and lithogenic sources of Pb in Lower Silesia (SW Poland), the Pb isotope composition was investigated in a spectrum of rocks and anthropogenic materials as well as within 10 soil profiles. Silicate rocks in Lower Silesia have 206Pb/207Pb ratios that vary from 1.17 for serpentinites to 1.38 for gneisses, and this variability is reflected in the isotope composition of the mineral soil horizons. The Pb isotope composition of coals, ores and anthropogenic materials (slags and fly ashes) is rather uniform, with 206Pb/207Pb ratios ranging from 1.17 to 1.18. Similar ratios were observed in ore and coal samples from Upper Silesia. The O soil horizons also have uniform 206Pb/207Pb ratios of 1.17–1.18 and the heterogeneity of the 206Pb/207Pb ratios increases with depth in the soil profiles. Five soils, with varying Pb concentrations, analysed far from contamination centres, show consistent, approximately 2-fold enrichment in Pb concentration from the C to A horizons, which is consistent with natural re-distribution of Pb within the profiles. The increase in the Pb concentration is accompanied by a decrease in 206Pb/207Pb ratios, also attributed to natural Pb isotope fractionation. Four soil profiles from industrial areas show variable enrichments in Pb concentrations and these are attributed to anthropogenic input from air-borne pollutants or even slag particles at smelting sites. The implication is that a lithogenic Pb source can deviate from the basement rock composition, and detailed isotope characteristics of the geological background and natural enrichments in soils are often needed to determine the lithogenic/anthropogenic proportions of Pb in soils. [Copyright &y& Elsevier]