藏南仲巴地体早奥陶世构造—热事件及其地质意义

发布时间：2018-11-10 12:01

【摘要】：仲巴地体是雅鲁藏布江缝合带西段南北蛇绿岩带之间的重要构造单元,目前对其是否存在早古生代构造-热事件记录及构造属性判别尚不明确.通过野外观测、岩石地球化学研究和年代学分析,在仲巴地体中段的公珠错一带识别出一套侵入到黑云斜长片麻岩中的片麻状二长花岗岩,其锆石U-Pb年龄为~478Ma,表明岩石形成时代为早奥陶世;该套花岗岩具有高Si、富Al和总碱含量较高的特点,铝饱和指数A/CNK=1.13~1.20,富集大离子亲石元素Rb、K,相对亏损Ba、Sr、Nb、Ti等,属于钙碱性强过铝质花岗岩.这是首次在雅鲁藏布江缝合带西段仲巴地体内部识别出代表早奥陶世构造-热事件的地质记录,该套花岗岩形成过程与原特提斯洋向冈瓦纳大陆北缘俯冲结束后的上地壳熔融相关,证明仲巴地体在早古生代应为东冈瓦纳大陆北缘的组成部分.
[Abstract]:The Zhongba terrane is an important tectonic unit between the northern and southern ophiolite belts in the western section of the Yarlung Zangbo River suture belt. At present, it is not clear whether there are early Paleozoic tectonic-thermal events and tectonic attributes. Based on field observations, geochemistry and geochronology, a set of gneiss intruded into the gneiss in the middle of the Zhongba terrane has been identified. Its zircon U-Pb age is ~ 478Ma. It shows that the age of rock formation is early Ordovician; This set of granite has the characteristics of high Si, rich Al and high total alkali content. The aluminum saturation index A / CNK 1.13 ~ 1.20 and the enrichment of large ion lithophile element Rb,K, are relatively depleted Ba,Sr,Nb,Ti and belong to calc-alkaline strong peraluminous granites. This is the first time that a geological record representing the early Ordovician tectonic-thermal events has been identified in the Zhongba body of the western section of the Brahmaputra suture belt. The formation process of the granites is related to the melting of the upper crust after the subduction of the original Tethys ocean to the northern margin of Gondwana continent, which indicates that the Zhongba terrane should be an integral part of the northern margin of East Gondwana in the early Paleozoic.
【作者单位】：中国地质大学全球大地构造中心;中国地质大学地球科学学院;中国地质调查局青藏高原地质研究中心;东华理工大学地球科学学院;
【基金】：中国地调局青藏高原地质研究中心开放课题(Nos.21201010000150014-28,21201010000150014-29) 西藏1∶5万公珠错东地区4幅区域地质矿产调查项目(No.1212011221066) 国家自然科学基金项目(Nos.41603031,41272078)
【分类号】：P534.42

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