西藏南部康马花岗岩锆石SHRIMP U-Pb年龄

U-Pb SHRIMP ZIRON AGES OF THE KANGMAR GRANITE IN THE SOUTHERN TIBET

康马花岗岩体位于西藏南部拉轨岗日岩带的中部,地质研究程度较高。本文主要探讨康马片麻状二云母花岗岩成因及其形成时代。二云母花岗岩中锆石CL图像发育有规则的韵律生长环带,表明其为典型的岩浆锆石;另锆石中Th/U比值稳定、较高的特点,也说明二云母花岗岩为岩浆成因;对锆石进行SHRIMP U-Pb定年,结果为493 Ma±14 Ma(MSWD=1.00),相当于早奥陶世,该年龄即是康马片麻状二云母花岗岩结晶时间,表明在拉轨岗日岩带中部存在加里东期岩浆作用。文章最后对康马岩体片理化的时间和成因等问题进行了探讨,认为康马岩体片理化的时间为中新世,其成因与印度-欧亚陆陆碰撞、地壳缩短而产生的变形变质作用有关。

The Kangmar gneisic two-mica granite lies in the middle of Laguigangri rock belt, southern Tibet. This paper mainly discussed the characters of the genesis and formation age of the Kangmar pluton. The crystallized rhythm zones in the zircons＇ CL images indicated that the zircons were typical magmatic zircons,which was proved by the high and stable Th/U ratios of these zircons. The zircon SHRIMP U Pb dating result of Kangmar gneisic two-mica granite was 493 Ma±14 Ma, MSWD= 1.00, consistent with the Ordovician epoch, belonging to Caledonian period. For these zircons were typical magmafic zircons, this age was the formation time of the Kangmar pluton,which implied there was a magma event in the middle of Laguigangri rock belt during the Caledonian period. Finally,the genesis and the metamorphic time of the Kangmar pluton were discussed. It was considered that the metamorphism of Kangmar rock body related to India-Eurasia collision and occurred in Miocene period.