羌塘盆地变质岩锆石SHRIMP U-Pb年龄及其地质意义

摘要

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.%笔者在位于北羌塘的玛尔果茶卡发现了具有区域变质特点的副变质岩组合,岩性为含蓝晶石矽线石长英质片麻岩、含蓝晶石夕线石绢云母石英片岩.1∶25万区域地质调查将这套岩石命名为前奥陶纪齐陇乌如岩组,呈断续出露的小型穹隆分布在中央隆起带北缘附近.笔者对片麻岩中的锆石进行了SHRIMP年龄分析,获得锆石年龄347～2827Ma.本文对不同年龄段所反映的构造热事件及其地质意义进行讨论.