The Eastern Erzgebirge sensu strictu represents a volcano-tectonic depression, which may be described as a paleo-caldera, the Altenberg-Teplice caldera of trap-door type (Benek, 1991). New geochemical and geochronological data and a synthesis first based on a regionally quite complete data set using results from several prospecting decades are a fundamental key for the current discussion and understanding of the role of volcanics in the petrogenetic and metallogenic evolution of this crustal unit.
Late-Variscan crustal evolution in the Eastern Erzgebirge is characterized by intense fracture tectonic activation forming graben and horst systems. The faults produced trend NNW and NE and control multiple intrusive and extrusive felsic magmatism. The dominant element in the area is the 20 km long, NNW-trending Teplice Rhyolite complex (TR). With the same orientation this is followed by the subvolcanic intrusion of the so-called Altenberg Granite Porphyry (GP), a more rhyodacitic unit in particular with some cumulate features. The caldera stage is followed by Li-F granite intrusions.
The maximal thickness of the dominantly pyroclastic TR unit amounts to 1000 m. Besides ignimbrites also lava flows, tuffs, tuffites, and sedimentary layers of intra-volcanic playa character occur.
The eruption of the TR ignimbrites took place as a westward directed blast. The step-by-step formed caldera collapse is figured by increasing thickness of the rhyolites towards the eruption centre(s) situated along a NNW trending deep fault, the Meissen-Teplice line.
The distribution of the pyroclastics from the margins of the caldera to the NNW striking eruption centre represents the depositional zoning. Using data from lithogeochemical mapping in the study area, Zr, Ba, TiO2 and Sr characterize best the petrogenetic zonation of the volcanics, e.g. of the effusives and extrusives in the lithogeochemical map, as well as serve as a fundamental key to reconstruct the fractionation patterns, the vertical zonation and the eruption mechanisms of the magma chamber(s).
Li and especially high Rb contents reflect the hidden granite relief below the (sub)volcanic depositions, in particular the elevations of the albite-zinnwaldite granites intruding into the rhyolite and gneiss units.
Additionally, geochemically investigated drilling profiles (Rb, Sr, Zr) including the whole eruptive sequence could be used to identify the petrochemical evolution patterns of the TR in general (reversed zonation) and to show the same trend for single extrusive events, too. Whereas Rb-rich units reflect Rb accumulation in micas and feldspars (the first eruption stages of each cycle), is Zr representing the final eruption stages up to the formation of cumulates. The whole evolution shows a reversed zoned magma chamber producing regardless the observed trends heterogenous volcanic products.
Benek, R., Z. Geol. Wiss. 19, 379-389 (Berlin, 1991).