雅鲁藏布江缝合带西段普兰地幔源区特征  

Characteristics of source of the Purang pyrolite in the western Yarlung-Zangbo suture zone

作　　者：胡杰 钟宏[1,2] 阮涛 郑石基 柏中杰 HU Jie;ZHONG Hong;RUAN Tao;ZHENG Shi-ji;BAI Zhong-jie(State Key Laboratory of Deposit Geochemistry,Institute of geochemistry Chinese Academy of Sciences,Guiyang 550081,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地球化学研究所,矿床地球化学国家重点实验室,贵州贵阳550081 [2]中国科学院大学,北京100049

出　　处：《矿物学报》2022年第5期590-604,共15页Acta Mineralogica Sinica

基　　金：第二次青藏高原综合科学考察研究(编号:2019QZKK0806);国家杰出青年基金(编号:41425011)。

摘　　要：普兰蛇绿岩位于西藏雅鲁藏布江缝合带西部,岩体出露面积约800km~2,是雅江蛇绿岩带上为数不多的保存完好、岩石新鲜度高的大岩体之一。目前对于普兰地幔为弧下地幔或MORB地幔,还是大陆岩石圈地幔仍存在分歧,其形成时是否存在洋内俯冲以及地幔深循环等地幔动力学过程的了解也不够充分。本文对普兰地幔岩展开精细的岩石学、矿物学和地球化学研究,初步探讨普兰地幔源区性质和地幔过程。结果表明,普兰二辉橄榄岩具有深海橄榄岩的特征,经历10%~15%的部分熔融,而方辉橄榄岩与弧前橄榄岩类似,并经历13%~25%的部分熔融。普兰地幔岩具“V”型原始地幔标准化稀土配分模式,显著富集不相容元素,如轻稀土元素、部分高场强元素(Hf、U、Pb等)和大离子亲石元素(Rb、Sr等)。我们认为这种富集特征源自俯冲含水熔体的交代作用,普兰地幔是一个经历了洋内俯冲过程的弧下地幔。The Purang ophiolite, located in the western Yarlung-Zangbo suture zone(YZSZ), with the covered area of 800 km~2, is one of the largest massifs with well-preserved and fresh mantle peridotites in the YZSZ. It is still debated whether the source of Purang pyrolites belongs to the sub-arc mantle, the MORB mantle, or the subcontinental lithospheric mantle, and it is poorly understood whether there was the intra-ocean subduction or the deep mantle cycling of mantle geodynamic processes at the time of the formation of Purang pyrolites. In this study, we have conducted detailed petrological, mineralogical and geochemical studies of the Purang pyrolites, and have preliminarily explored the nature and related mantle dynamic processes of the source of Purang pyrolites. The results show that the lherzolite in the Purang area has similar geochemical characteristics of the abyssal peridotite and had experienced 10%-15% partial melting, while the harzburgite has similar characteristics of the fore-arc peridotite and had experienced 13%-25% partial melting. The Purang pyrolites are characterized with “V-shaped” primitive mantle-normalized REE patterns, and are significantly enriched in incompatible elements such as LREEs, high field strength elements(e.g., Hf, U, Pb) and large ion lithophile elements(e.g., Rb and Sr). We have suggested that this feature of the enrichment of incompatible elements in the Purang pyrolites was resulted from the metasomatism of the mantle by subduction-related hydrous melts and the source of Purang pyrolites could be a sub-arc mantle which had been experienced the intra-ocean subduction process.

关 键 词：雅鲁藏布江缝合带 地幔橄榄岩 俯冲过程 弧地幔 普兰 

分 类 号：P585.1[天文地球—岩石学] P584[天文地球—地质学] P595