【作者】 金贵善；

【导师】 宋彪； 陈文；

【作者基本信息】 中国地质科学院 ， 地球化学， 2006， 硕士

【摘要】 为了解古特提斯在西金乌兰-金沙江缝合带西段的地质演化历史,本文对与古特提斯有关的重要岩石进行了地球化学和SHRIMP锆石U-Pb年龄研究。为此,在野外地质调查的基础上,采集了与古特提斯洋有关的岩浆岩,包括玄武岩、石英闪长岩、蛇绿岩套中的辉长岩等,以及印度板块与欧亚板块碰撞的远程效应产生的粗面岩及花岗岩。对这些样品进行了地球化学及同位素年龄分析,取得如下进展:1.聂恰曲蛇绿岩组合中的辉长岩具有洋中脊玄武岩的地球化学特征,获得该蛇绿岩辉长岩的锆石U-Pb年龄为268±11 Ma。2.杂多纪查能基性-超基性岩为钙碱性系列,其中辉长岩中的锆石U-Pb年龄为252±6 Ma。通过与同期埃达克岩的对比,说明这类岩石是晚二叠世古特提斯洋壳俯冲形成的产物。3.将玉树-治多一带印支期花岗岩体的侵入时间厘定为209±4 Ma,即为晚三叠世。地球化学特征显示其可能形成于火山弧环境,为板块俯冲的产物。这表明沿西金乌兰-金沙江缝合带的玉树-治多一带,迟至晚三叠世,古特提斯残余洋壳的俯冲作用及伴随的板块碰撞作用可能仍在继续。4.杂多特龙赛火山岩以钙碱性为主,形成于陆缘的火山弧环境,并可能是古特提斯残余洋壳俯冲于杂多微陆块之下的产物,其喷发时间为217±9 Ma,属于晚三叠世。5.在聂恰曲蛇绿岩组合中的辉长岩中测得元古代残留锆石,说明基底物质可能参与了该地质作用过程。6.根据锆石的U-Pb年龄,确定下拉秀火山岩的喷发时间为50±1 Ma,白马海花岗岩体侵位时间为49±1 Ma。二者可能是印度板块与欧亚板块俯冲碰撞的远程效应的产物。更多还原

【Abstract】 In order to know the evolution history of the west of the Xijir Ulan-Jinshajiang suture zone, some rocks closely related with the Paleo-Tethys were studied in geochemistry and geochronology.On the base of field geological surveys, the magmatic rocks with the Paleo-Tethys, such as basalts, quartz diorites, gabbros from the ophiolites, and trachytes and granites formed by collision of India Plate and the Eurasian Plate, and so on, were collected. By the U-Pb SHRIMP dating and geochemical analyzing of the samples, the following conclusions were obtained:1. The gabbro of Nieqiaqu ophiolite has the specialties of MORB and the zircon from the rock gave a ²⁰⁶Pb/²³⁸U age of 268±11 Ma.2. The compages of Jizaneng basic-ultrabasic rocks in Zaduo County belongs to calc-alkaline series. The zircon in the gabbro from the compages gave a ²⁰⁶Pb/²³⁸U mean age of 252±6 Ma. The rock might be produced by the subduction of the oceanic crust of Paleo-Tethys in Late Permian contrasting with the contemporary adakite.3. The Indosinian granites at Yushu-Zhiduo area were dated as 209±4 Ma. The geochemical characters indicated that they might be formed in volcanic arc environment by the Plate subduction. So, it is believed that, along the Xijir Ulan-Jinshajiang suture zone, the subduction of the crustal remnants of the Paleo-Tethys, with concomitance of the plate collision, were still carried on until Late Trias.4. Telongsai volcanic rocks in Zaduo County, mainly belonging to the calc-alkaline series, were formed in epicontinental volcanic arc environment, possibly brought by the subduction of the residual oceanic crust of Paleo-Tethys to Zaduo micro-continents, and the U-Pb age of the zircon indicated that the volcano erupted at 217±9 Ma.5. The remnant zircons, being of Proterozoic ages, were found in the gabbro of Nieqiaqu ophiolites, which showed that the material of the basement might take part in the process of the formation of the ophiolites.6. After measuring zircon U-Pb age precisely, it was confirmed that the Shanglaxiu volcano eruption should be at 50±1 Ma, and the Baimahai granite was emplaced at 49±1 Ma. Both of them might be produced by the long-distance effects of the subduction collisions between the Indian Plate and Eurasian Plate.更多还原