藏南冈底斯带西段麦拉花岗岩锆石SHRIMP定年及地质意义

用SHRIMP测定了冈底斯岩带西段麦拉山口岩体同碰撞黑云母二长花岗岩锆石的U-Pb年龄,黑云母二长花岗岩锆石SHRIMP U-Pb年龄为47.1±1.1Ma。这就为前人提出的雅鲁藏布江地区洋盆闭合、板块开始碰撞的时间为50Ma左右提供了同位素年代学的证据。

SHRIMP ZIRCON U-PB DATING OF GRANITES IN MAILA,WEST OF THE GANGDISE BELT,SOUTHERN TIBET AND ITS GEOLOGICAL IMPLICATION

The Maila Pluton is located at the northwest of Zhongba County, west of the Gangdise belt. The pluton contacts the Late Palaeozoic strata with the fault in the south; while the pluton invades in the Cretaceous red silicalite in the north. According to the lithologic and mineralogic characteristics it is classified as biotite adamellite. Most of the potassium feldspar and plagioclase phenocrysts are endural. Chemically, the pluton has the characteristics of high-Ti and moderate Al contents. SHRIMP zircon U-Pb dating techniques is applied to the Maila Pluton in this study. The result shows the formation time of the Maila pluton is 47.1±1.1Ma. Most researchers think the plate collision began 50Ma ago, so the Maila pluton may belong to syn-collision granite. The beginning time of collision is a little earlier than the invasion time of the syn-collision granite, the dating of the Maila pluton also provides an isotopic evidence, which suggests the suture of the YalungZangbo oceanic basin and the beginning of plate collision was about 50 million years ago.