青藏高原羌塘中部果干加年山一带晚三叠世花岗岩的特征、锆石定年及其构造意义

藏北羌塘果干加年山的东部出露有一处花岗岩岩体,其主要岩性为黑云母二长花岗岩和花岗细晶岩岩脉,侵入晚三叠世望湖岭组和晚石炭世—早二叠世展金岩群之中。锆石LA-ICP-MS U-Pb年龄测定结果表明,该花岗岩的形成时代为晚三叠世（210.3Ma±2.6Ma）,略晚于区域上高压变质带的变质峰期年龄和望湖岭组底部流纹岩的年龄。岩石地球化学数据显示,该花岗岩岩体属高钾钙碱性过铝质花岗岩,形成于后碰撞环境,是岩石圈碰撞加厚之后减压过程中岩浆活动的产物,说明在210Ma左右果干加年山地区的构造环境开始由碰撞阶段向板内阶段转化,进入了后碰撞阶段。

Characteristic,zircon dating and tectonic significance of Late Triassic granite in the Guoganjianianshan area,central Qiangtang,Qinghai-Tibet Plateau,China.

The granite rock body located in Guoganjianianshan area,Qiangtang,Northern Tibetan Plateau mainly includes biotite adamellite and granite aplite dike and intrudes into Late Triassic Wanghuling Formation and Late Carboniferous-Early Permian Zhanjin Group-complex.LA-ICP-MS U-Pb dating were carried on the zircons of this granite rock body and the dating results showed that it was formed in Late Triassic（210.3Ma±2.6Ma）.This age is slightly later than the metamorphic peak time of the high-pressure metamorphic belt in this area and the age of the rhyolite in lower Wanghuling Formation.Geochemistry studies indicate that this granites belong to high-potassium peraluminous calc-alkaline granites and were formed in post-collisional tectonic setting and by the magmatic activity of the decompression process after the collision and thickening of lithosphere,which means that the tectonic setting of Guoganjianianshan area was transforming from collision stage to intraplate stage and entered post-collision stage.