青海尖扎—同仁地区隆务峡蛇绿岩的形成时代及意义——来自辉长岩锆石LA-ICP-MS U-Pb年龄的证据  

LA-ICP-MS zircon U-Pb dating of the gabbro from Longwu Gorge ophiolite,Jianzha-Tongren area,Qinghai,China and its geological significance

作　　者：王绘清[1] 朱云海[1] 林启祥[1] 李益龙[1,2] 王坤[1] 

机构地区：[1]中国地质大学(武汉)地球科学学院,湖北武汉430074 [2]中国地质大学/地质过程与矿产资源国家重点实验室(武汉),湖北武汉430074

出　　处：《地质通报》2010年第1期86-92,共7页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:1212010610316)资助

摘　　要：隆务峡蛇绿岩位于青海省同仁县,大地构造位置处于西秦岭和南祁连造山带的结合部位。蛇绿岩年代学对于研究造山带构造演化和恢复古洋-陆板块构造格局至关重要。对隆务峡蛇绿岩中的辉长岩进行了LA-ICP-MS锆石U-Pb定年,206Pb/238U加权平均年龄为250.1Ma±2.2Ma(MSWD=0.7),代表了辉长岩的结晶年龄,表明隆务峡蛇绿岩是晚二叠世—早三叠世西秦岭与南祁连之间古洋盆扩张过程中岩浆活动的产物。而呈岩株侵入到蛇绿岩中的花岗闪长岩的年龄(244Ma±1.4Ma)晚于蛇绿岩中辉长岩的年龄,但早于区域上大量存在的印支期花岗岩,可能记录了蛇绿岩的侵位时代。Longwu Gorge ophiolite belt located in Tongren Area,Qinghai Province,is at the jointing part of West Qinling and South Qilian orogenic belts. The ophiolite geochronology is very important for the study of tectonic evolution of orogenic belt and the reconstruction of the ancient ocean-land and plate tectonic framework. LA-ICP-MS zircon U-Pb dating of gabbro from the Longwu Gorge ophiolite suggests an isotopic age of （250.1±2.2）Ma （MSWD=0.7）,which indicates that the Longwu Gorge ophiolite was the product of magmatic activitiy during the process of extension of paleo-ocean basin along the jointing part of West Qinling and South Qilian in the late Permian to early Triassic. Zircons from the granodiotite intruding the ophiolite yielded an age of 244±1.4Ma,which was younger than the formation of ophiolite,but it is significantly older than the Indosinain collisional granitoids in the region. There-fore,it may reflect the emplacement age of the Longwu Gorge ophiolite.

关 键 词：蛇绿岩 辉长岩 LA-ICP-MS锆石U-PB年龄 西秦岭造山带 南祁连造山带 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]