今天是2018年10月18日

西藏雅鲁藏布江缝合带西段达巴蛇绿岩年代学、地球化学特征及其构造意义

DOI:10.3799/dqkx.2018.703

作者:程晨,夏斌,郑浩,袁亚娟,殷征欣,陆野,徐迟,张霄

联系地址:中山大学海洋科学学院,广东广州 510006

摘要:达巴蛇绿岩位于雅鲁藏布江蛇绿岩带西段南亚带,主要由地幔橄榄岩、基性岩脉和硅质岩组成,其形成时代和构造背景尚不清楚.首次报道了达巴蛇绿岩中基性岩脉的岩石学、锆石U-Pb 年代学、全岩地球化学数据.达巴辉长岩和辉绿岩具有高的Al和Mg、低Ti、K和P,为低钾钙碱性玄武质岩石.岩石具有与N-MORB一致的稀土配分模式,但是N-MORB标准化蛛网图中显示Nb负异常,显示了受到俯冲板片流体的影响.辉绿岩的锆石U-Pb年龄为120.0±1.7 Ma,为早白垩世晚期,地球化学特征显示源自于低程度的尖晶石相地幔源区的部分熔融.结合前人研究成果,认为达巴蛇绿岩形成于与初始俯冲有关的弧前扩张中心,是受到俯冲板片流体交代的上覆地幔楔部分熔融的产物.

关键字:雅鲁藏布江缝合带;达巴蛇绿岩;地球化学;锆石U-Pb定年;构造环境

Chronology, Geochemistry and Tectonic Significance of Daba Ophiolites in Western Segment of Yarlung Zangbo Suture Zone, Tibet

Author:Cheng Chen, Xia Bin, Zheng Hao, Yuan Yajuan, Yin Zhengxin, Lu Ye, Xu Chi, Zhang Xiao

Author Address:School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China

Abstract:The Daba ophiolite is located in the southern sub belt of the western segment of the Yarlung Zangbo suture zone (YZSZ) and mainly composed of mantle peridotite, mafic dikes and siliceous rocks. Its formation time and tectonic setting are not clear. This is the first report of zircon U-Pb age, petrologic and whole-rock geochemical data from the Daba ophiolite. The major elements of Daba gabbro and dolerite are characterized by high contents in Al, Mg and low contents in Ti, K and P, which belong to subalkaline basalt. The REE distribution patterns are very similar to those of the normal mid-ocean ridge basalt (N-MORB). However, the normalized spider diagram shows significant depletion of Nb, suggesting the influence of fluids from downgoing slab.The dolerites yielded zircon U-Pb ages of 120.0±1.7 Ma, and geochemical features show partial melting from the low degree spinel bearing mantle source. Combining with previous studies, it is suggested that the intrusion of the mafic rocks into the Daba peridotites may be interpreted as a result of mixing process between MORB like melts and arc derived fluids, which may have occurred during the stage of subduction initiation in an extending forearc region.

Keyword:Yarlung Zangbo suture zone; Daba ophiolite; geochemistry; zircon U-Pb age; tectonic setting

 

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作者简介:程晨(1988-),女,博士后,主要从事岩石学和地球化学研究.ORCID: 0000-0003-3478-0175. E-mail: cc37767484@126.com

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