SHRIMP zircon U-Pb ages and their geological implications for the metamorphic rocks in the Qiangtang Basin

The parametamorphic rocks characteristic of regional metamorphism are observed in Margog Caka, northern Qiangtang Basin. Lithologically, the parametamorphic rocks are assembled by felsic gneiss containing kyanite and sillimanite and sericite quartz schist containing kyanite and sillimanite, and entitled to the name of the pre-Ordovician Qilongwuru Group Complexes based on the 1:250 000 regional geological survey. These rocks occur as isolated small domes along the northern margin of the central uplift zone. The SHRIMP U-Pb ages for the zircons from the gneiss range between 347 Ma and 2827 Ma. The zircons have complex genetic types, including magmatic zircon, metamorphic zircon and anatectic zircon. However the metamorphim ages and protolith ages of the zircons remain uncertain. The SHRIMP U-Pb age of 2827 Ma indicates that the zircons originated from the Mesoarchean, during which the tectonic thermal events once occurred in the Qiangtang Basin. The present paper deals, in detail, with the tectonic thermal events of varying ages and their geological implications.