班公湖中特提斯洋向南俯冲的时限:来自SSZ型辉长岩的制约

发布时间：2018-03-17 01:41

  本文选题：辉长岩　切入点：锆石U-Pb年代学　出处：《大地构造与成矿学》2017年05期 　论文类型：期刊论文

【摘要】：班公湖-怒江中特提斯洋的俯冲极性和俯冲时间一直存在争议。作者通过野外地质调查、岩相学、锆石U-Pb年代学及岩石地球化学研究,从西藏班公湖蛇绿混杂岩带中识别出一套早白垩世SSZ型蛇绿岩,岩石组合上主要由辉长岩和玄武岩组成,还有少量的硅质岩和超基性岩。本文对辉长岩进行了全岩主、微量元素地球化学及LA-ICP-MS锆石U-Pb年代学研究。地球化学组成特征显示,辉长岩富集轻稀土元素,重稀土元素平坦,相对富集大离子亲石元素,高场强元素存在一定亏损;Th/Ta比值与岛弧玄武岩相似(Th/Ta1.6),Ta/Hf比值较高(0.1),显示其既保留了俯冲环境的地球化学特征,也提供了伸展构造环境的信息。辉长岩中锆石U-Pb加权平均年龄为129.2±0.4 Ma(MSWD=0.36),该年龄是班公湖-怒江缝合带中迄今报道的最年轻蛇绿岩年龄。结合区域地质背景,认为这套蛇绿岩形成于班公湖-怒江古洋盆西段向南俯冲形成的弧前盆地,而班公湖-怒江古洋盆北向俯冲可能始于早侏罗世,晚侏罗世形成双向俯冲格局,直到早白垩世洋盆关闭,晚白垩世进入陆内构造环境。
[Abstract]:The subduction polarity and subduction time of the Tethys ocean in the Bangong Lake-Nujiang River have always been controversial. The authors studied the geochemistry and geochemistry of zircon by means of field geological survey, petrography, zircon U-Pb geochronology and geochemistry. A set of early Cretaceous SSZ ophiolite was identified from the Bangonghu ophiolite melange belt in Tibet. The rock assemblage consists mainly of gabbro and basalt, and a small amount of siliceous and ultrabasic rocks. Trace element geochemistry and LA-ICP-MS zircon U-Pb geochronology. Geochemical composition features show that gabbro is rich in light rare earth elements, heavy rare earth elements are flat, and relatively rich in large ion lithophile elements. The Th / Ta ratio of the high field strength elements is similar to that of the island arc basalts, and the ratio of Th / Ta / Ta / HF is higher than that of the island arc basalts, indicating that it retains the geochemical characteristics of the subduction environment. The U-Pb weighted mean zircon age in gabbro is 129.2 卤0.4 Mai MSWDU 0.36, which is the youngest ophiolite age reported to date in the Bangong Lake-Nujiang suture zone, in combination with the regional geological background, and the zircon U-Pb weighted mean age is 129.2 卤0.4 Mai, which is the youngest ophiolite age ever reported in the Bangong Lake-Nujiang suture zone. It is considered that the ophiolite was formed in the forearc basin which subducted southward in the western section of Bangong Lake-Nujiang ancient ocean basin, while the northward subduction of Bangong lake-Nujiang ancient ocean basin probably began in the early Jurassic and formed a bidirectional subduction pattern in the late Jurassic. The oceanic basin was closed until the early Cretaceous, and the late Cretaceous entered the continental tectonic environment.
【作者单位】： 南方石油勘探开发责任有限公司;中国地质大学(武汉)地质调查研究院;中国地质大学(武汉)地球科学学院;中国地质大学(武汉)青藏高原研究中心;
【基金】：中国地质调查局西藏1∶50000聂拉木等4幅地质图区调(1212011121242) 1∶50000日土县卡易错地区4幅地质图区调(1212011121246) 油气资源与探测国家重点实验室开放基金(KFKT2010-5)联合资助
【分类号】：P542;P588.124
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本文编号：1622626