Polymetamorphism of the Variscan Basement of the Moldanubian Black Forest (Germany) Docume

Polymetamorphism of the Variscan Basement of

the Moldanubian Black Forest (Germany) Documented in Zircon and Garnet Minerals from

Gneisses

陈福坤

【期刊名称】《中国地球化学学报（英文版）》 【年(卷),期】2002(021)002

【摘要】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