柴北缘牦牛山地区辉绿岩体锆石U-Pb年龄及地质意义

青海乌兰县境内牦牛山辉绿岩体为一沿北西向构造线展布椭圆形岩体,侵位于晚泥盆世牦牛山组含砾砂岩及砾岩中。岩体风化蚀变为灰色,受后期改造不明显,未见显著变形特征;镜下观察其具辉绿结构、块状构造,主要矿物为斜长石、单斜辉石。用LA-ICP-MS方法,对牦牛山辉绿岩体中的灰绿玢岩进行锆石U-Pb测年分析,同位素测年及CL图像结果显示,本组锆石可以分为八组:～3. 2 Ga、～2. 36 Ga、～1. 9 Ga、～540 Ma、～460 Ma、～400 Ma、～350 Ma、～250 Ma,在此基础上,认为研究区作为欧龙布鲁克地块的一部分,其深部地质信息较复杂,既有太古宙及元古宙变质基底的岩浆热事件信息,又经历了加里东和印支期两次洋陆俯冲事件的叠加,使得研究区构造演化复杂化。

Zircon U-Pb geochronology and geological significance of diabase rocks in Maoniushan area of North Qaidam Basin

Maoniushan diabase is a elliptic intrusive which distributes along the northern west tectonic line in Wulan of Qinghai province. It invades in the gravel sandstone and conglomerate of Maoniushan group. The intrusive rock exposes in Maoniushan area in Wulan,and is weatheringed into gray.Later period transformation and deformation is not obvious.The rock has ophitic texture and massive structure and the main minerals are plagioclase and traversellite. The zircon U-Pb dating which is in the allgovite of Maoniushan diabase is performed with LA-ICP-MS and the isotopes data and CL image results showed that The zircon can be divided into eight groups:~3.2 Ga,~2.36 Ga,~1.9 Ga,~540 Ma,~460 Ma,~400 Ma,~350 Ma,~25 0Ma. On this basis, it is considered that the study area, as a part of the Oulongbuluke block, has deep geological information, including both magmatic thermal event information of the Archean and Proterozoic metamorphic bases, and also experienced the Caledonian Period and Indochina Period.The superposition of ocean-land subduction complicates the structural evolution of the study area.