Quartz and feldspar zoning in the eastern Erzgebirge volcano-plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing

Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera biotite granites and the rhyodacitic Schönfeld volcanic rocks represent temporally and spatially separate magma sources. However, the deep magma reservoir of both is assumed to have been at a depth of 24-17 km. The drastic chemical contrast between the pre-caldera Schönfeld (Westfalian B-C) and the syn-caldera Teplice (Westfalian C-D) volcanic rocks is related to the change from late-orogenic geotectonic environment to post-orogenic faulting, and is considered an important chronostratigraphic marker.