Polymetamorphism of the Variscan Basement of the Moldanubian Black Forest (Germany) Documented in Zircon and Garnet Minerals from Gneisses

t Tübingen Wilhelmstrasse 56,72074 Tübingen, Germany)2) (Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China) Abstract: High-grade metamorphic Variscan basement is exposed in the Moldanubian zone of the Black Forest (BF), being the internal zone of the European Variscan belt. Zircon grains from K-rich felsic orthogneisses and an anatectic paragneiss in the Moldanubian Black Forest demonstrate a multi-stage crystallization at ～600 Ma, ～480 Ma, ～400-380 Ma, and \{～350\} Ma. The last three stages of crystallization probably represent metamorphic overprint during pre-Variscan and Variscan metamorphism. Using stepwise leaching procedures, garnet minerals from felsic orthogneisses as well as paragneisses in the Moldanubian Black Forest yielded Early Carboniferous Sm-Nd ages (～330-340 Ma), which are consistent with the well-constrained Variscan HT metamorphic event, and Early Palaeozoic (～480 Ma) to Devonian (～400-370 Ma) Pb-Pb ages. The coincidence of growth time for zircon and garnet minerals at Early Palaeozoic is interpreted as dating a metamorphic event. These garnet data demonstrate that the Moldanubian BF basement underwent at least two metamorphic events during the Early Palaeozoic and Early Carboniferous. During the Variscan HT metamorphism, the Sm-Nd system of garnet was disturbed, but not the U-Pb system, implying the peak metamorphic temperature was lower than ～800℃.