藏南吉隆地区早古生代大喜马拉雅片麻岩锆石SHRIMP U-Pb年龄、Hf同位素特征及其地质意义

藏南吉隆地区眼球状片麻岩是大喜马拉雅结晶岩系的一部分，其矿物组成为石英、斜长石、钾长石、黑云母和少量的白云母。片麻岩中的锆石具有核边结构，由继承碎屑锆石核和具有同心环带结构的岩浆锆石边组成，SHRIMP U Pb测年显示，边部岩浆锆石加权平均年龄为（4989±44） Ma，表明片麻岩的原岩为早古生代的花岗岩，εHf加权平均值为-83±095，暗示片麻岩原岩为壳源，可能是印度大陆北部地壳部分熔融的产物。文中和现有的地质年代学数据表明，喜马拉雅造山带是一个复合造山带，经历了早古生代的造山作用，早古生代的喜马拉雅造山带是原特提斯洋向冈瓦纳大陆北缘俯冲的结果，是冈瓦纳大陆拼合之后在其边缘形成的安第斯型造山带，而不属于冈瓦纳超大陆聚合过程中陆陆碰撞形成的泛非造山带的一部分。

Zircon SHRIMP U-Pb ages,Hf isotopic features and their geological significance of the Greater Himalayan Crystalline Complex augen gneiss in Gyirong Area,south Tibet

The augen gneiss in the Gyirong Area of south Tibet belongs to the Greater Himalayan Crystalline Complex.It consists of quartz,plagioclase,K-feldspar,biotite and minor muscovite.Zircons of the augen gneiss have core-rim structures with inherited cores and magmatic rims indicated by concentric oscillatory zoning.The zircon rims gave a weighted mean age of 498.9±4.4 Ma,hinting that the protoliths of the gneiss was early Paleozoic granite.The εHf ranges between-13.6 and-4.6 with a weighted mean value of-8.3±0.95.It implies that the source of granite came from crust,possibly resulted from partial melting of the crust in the northernmost margin of the India Craton.The zircon SHRIMP U-Pb ages,combined with the published geochronological data,demonstrate that the Himalaya is a composite orogenic belt,which underwent an early Paleozoic orogenesis.The early Paleozoic Himalaya was an Andean-type orogen after the Gondwana assemblying,which resulted from the subduction of the proto-Tethys ocean beneath the India Plate,rather than a Pan-African orogen that was formed by the continent-continent collision during the Gondwana assembly.