Diachronous pulses of Variscan magmatic activity in the Eastern and Western Erzgebirge (Germany and Czech Republic), their temporal geochemical evolution, and their relation to ore formation

Two magmatic periods have been proposed in the Erzgebirge: a late Variscan (ca. 325–315 Ma) and a post-Variscan (ca. 300 Ma). Until now, only few data exist for the second period. We analyzed 13 samples from granites and rhyolites that have been suggested to belong to the second magmatic period. Zircons of these rocks were dated with the high-precision U–Pb chemical abrasion-isotope dilution-thermal ionization mass spectrometry. Seven samples belong to the post-Variscan period (305–296 Ma), among them are two granites that were not known before. A compilation of all high-precision zircon ages records distinct periods of magmatic activity in the Erzgebirge. Based on this compilation, we provide the first evidence that the magmatic evolution in the Erzgebirge was diachronous since magmatism occurred earlier in the Western Erzgebirge (323–313 Ma, 306–303 Ma) compared to the Eastern Erzgebirge (315–310 Ma, 301–296 Ma). In both parts of the Erzgebirge, these two magmatic stages are associated with abundant hydrothermal ore formation. Early Variscan melts are more magnesian compared to later and post-Variscan melts, which have ferroan and anhydrous character and commonly share some characteristics with A-type granites. The dominant protoliths of all Variscan melts were crustal quartzofeldspathic rocks with likely minor contribution of mantle material. Based on the earliest records of volcanic rocks, an earlier onset of uplift and exhumation of the eastern part of the Erzgebirge is assumed, whereas the uplift began later in the western part but reached deeper erosion at the present-day level.