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The Petrology, Geochemistry, and Petrogenesis of E-MORB-type Mafic Rocks from the Guomangco Ophiolitic Mélange, Tibet

查看全文 作　　者：XU [1]Mengjing;LI [1]Cai;WU [1]Yanwang;XIE [1]Chaoming 高影响力作者 机构地区：[1]College of Earth Science, Jilin University高影响力机构 出　　处：《Acta Geologica Sinica(English Edition)》索引2014年第88卷第5期,共17页高影响力期刊 基　　金：funded by the National Funds of Nature Science of China (Grant No. 41272240);the Project of China Geological Survey (Grant No. 1212011121248) 摘　　要：The Guomangco ophiolitic mélange is situated in the middle part of the Shiquanhe–Yongzhu–Jiali ophiolitic mélange belt(SYJMB) and possesses all the subunits of a typical Penrosetype ophiolite pseudostratigraphy. The study of the Guomangco ophiolitic mélange is very important for investigating the tectonic evolution of the SYJMB. The mafic rocks of this ophiolitic mélange mainly include diabases, sillite dikes, and basalts. Geochemical analysis shows that these dikes mostly have E-MORB major and trace element signatures; this is the first time that this has been observed in the SYJMB. The basalts have N-MORB and IAB affinities, and the mineral chemistry of harzburgites shows a composition similar to that of SSZ peridotites, indicating that the Guomangco ophiolitic mélange probably originated in a back-arc basin. The Guomangco back-arc basin opened in the Middle Jurassic, which was caused by southward subduction of the Neo-Tethys Ocean in central Tibet. The main spreading of this back-arc basin occurred during the Late Jurassic, and the basalts were formed during this time. With the development of the back-arc basin, the subducted slab gradually retreated, and new mantle convection occurred in the mantle wedge. The recycling may have caused the metasomatized mantle to undergo a high degree of partial melting and to generate EMORBs in the Early Cretaceous. E-MORB-type dikes probably crystallized from melts produced by about 20%–30% partial melting of a spinel mantle source, which was metasomatized by melts from low-degree partial melting of the subducted slab. 关 键 词：蛇绿混杂岩带 地球化学分析 西藏中部 岩石成因 B型 岩石学 基性岩 部分熔融程度
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