No abstract

No abstract

The post-Variscan thermal history of the Erzgebirge (Germany) is the result of periods of sedimentary burial, exhumation and superimposed hydrothermal activity. The timing and degree of thermal overprint have been analysed by zircon and apatite (U-Th)/He and apatite fission track thermochronology. The present-day surface of the Erzgebirge was exhumed to a near-surface position after the Variscan orogeny. Thermal modelling reveals Permo-Mesozoic burial to temperatures of up to 80-100°C, although the sedimentary cover thins out towards the north resulting in maximum burial temperatures of less than 40°C. This thermal pattern was locally modified by Cretaceous hydrothermal activity that reset the zircon (UTh)/He thermochronometer along ore veins. The thermal models show no significant regional exhumation during Cenozoic times, indicating that the peneplain-like morphology of the basement is a Late Cretaceous feature.

The Erzgebirge region of Germany records two major episodes of hydrothermal activity, which includes a Late Carboniferous to Early Permian event associated with significant Sn-W mineralization that is related to late Variscan granite magmatism, and a Mesozoic episode of polymetallic vein mineralization. In contrast to the first event, the age of the younger hydrothermal activity is poorly constrained. For the latter, various geochronological methods yielded a wide age range from Permian to early Tertiary. Here we apply fluorite (U-Th-Sm)/He thermochronology (FHe) on both types of mineralization with a twofold goal: (1) to investigate the sensitivity and applicability of the new FHe method (Evans et al., 2005), and (2) to constrain the thermal history of ore deposits in the Erzgebirge region. Two hundred and thirty-three aliquots from seven mineralization localities have been dated. Fluorite from six deposits yielded Cretaceous FHe ages between 112 to 79 Ma, which are independent of their paragenesis. In contrast, fluorite from the Sadisdorf Sn-W deposit yielded an age of 234 Ma. The younger ages are interpreted as cooling ages indicating the time of the last thermal overprint, including possible hydrothermal activity, in the Erzgebirge. The oldest, Triassic FHe ages at Sadisdorf indicate that the Mesozoic thermal overprint only partially reset the (U-Th-Sm)/He system of the late Variscan mineralization. Thermal modeling based on FHe ages and He diffusion parameters in fluorite results in thermal histories comparable to the results from the well-established apatite-based thermal modeling. This study emphasizes the applicability of fluorite (U-Th-Sm)/He thermochronology, which is especially suited for ore deposits where apatite is lacking. Regional Geology and Post-Variscan Tectonic Evolution The Erzgebirge forms an antiform structure exposing high-to medium-grade metamorphic gneisses in the core surrounded by a sequence of low-grade metamorphic units, mainly composed of micaschists and phyllites. This metamorphic assemblage formed by crustal stacking during the Carboniferous (e.g., Werner and Lippolt, 2000) and was later intruded by late-to post-Variscan granitoids and locally covered by rhyolites (Kossmat, 1925; Romer et al., 2007; see Fig. 1b). The Erzgebirge is bordered in the east by the Lausitz thrust to the Cadomian basement of the Lausitz block (Linnemann and Romer, 2002). This fault is sealed by Cretaceous deposits that formed at the margin of the synsedimentary uplifting block in the east. The initially flexural margin was later transformed into a thrust (Linnemann and Romer, 2010). The Eger fault delimits the Erzgebirge toward the south (e.g., Kroner et al., 2007; Fig. 1b). The post-Variscan

No abstract