雅鲁藏布江缝合带东段杰莎蛇绿岩中铬铁矿特征及其构造背景  

The Feature and Tectonic Setting of Chromitite from the Jiesha Ophiolite in the Eastern Yarlung-Zangbo Suture Zone in Tibet

作　　者：熊发挥[1] 杨经绥[1] 巴登珠[1] 高健[2] 来盛民 张岚[3] 

机构地区：[1]大陆构造与动力学重点实验室中国地质科学院地质研究所,北京100037 [2]昆明理工大学,昆明650504 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质学报》2016年第11期3099-3113,共15页Acta Geologica Sinica

基　　金：国家行业专项(编号SinoProbe-05-02);国家自然科学基金重点项目(编号40930313);国家自然科学基金创新群体项目(编号40921001);国家自然科学基金项目(编号41502062和41202036);中国地质调查局工作项目(编号DD20160023和2014DFR2127C);中国地质科学院地质研究所基本科研业务费(编号J1526)和IGCP-649项目联合资助成果

摘　　要：雅鲁藏布江缝合带东段加查县杰莎岩体主要由蚀变较强的方辉橄榄岩和纯橄岩、豆荚状铬铁矿组成。铬铁矿矿体呈东西向，倾向北西，矿体的围岩为纯橄岩及方辉橄榄岩，长20-40m，宽1～3m。镜下特征和电子探针分析结果显示铬铁矿中铬尖晶石的Cr#=67．9～88．5，Mg#值变化在64．6～68．2之间，TiO2含量为0．06％～0．18％，Al2O3含量为13．1％～16．5％，表明杰莎铬铁矿为高铬型铬铁矿。方辉橄榄岩中橄榄石、斜方辉石和单斜辉石的矿物化学特征表明杰莎岩体既具有深海地幔橄榄岩特征，也具有岛弧地幔橄榄岩的特点。并且依据铬尖晶石一橄榄石／单斜辉石的矿物化学成分，识别出杰莎岩体至少经历了2期过程，包括早期部分熔融（20％～30％）和晚期的岩石／熔体反应作用（〉35％）。因此，杰莎地幔橄榄岩和铬铁矿可能与雅鲁藏布江缝合带中其他岩体一样，经历了洋中脊及俯冲带的多阶段叠加的过程。The Jiesha mafic-ultramafic body is distributed mainly in the eastern Yarlung-Zangbo suture zone of Tibet. The massif consists of harzburgite, dunite, and podiform chromitite. Chromitite orebodies with a length of 20-40 m and a width of 1-3 m trend from east to west and dip northwest. The surrounding rocks are mainly harzburgites and dunites. Microscopic characteristics and electron microprobe analysis show that the chromian spinel in the Jiesha chromite has Cr# of 67.9-88.5 and Mg# of 64. 6-68.2, with TiO2 content of 0.06% - 0.18% and Al2O3 content of 13.1% - 16.5%, suggesting that the Jiesha chromite is high-Cr type chromite. Mineral chemistry of olivine, orthopyroxene and clinopyroxene in harzburgite shows that the Jiesha harzburgite are similar to abyssal peridotite and the fore-arc peridotite. Based on the chemical composition of spinel-olivine/clinopyroxene, it can be identified that the Jiesha mafic-ultramafic body had experienced early partial melting （degree about 20% -30%） and late rock/melt reaction （degree about 〉35%）. Therefore, the Jiesha peridotites and chromite, like other rock bodies in the Yarlung Zangbo suture zone, might experience multi-stage superimposition processes such mid-ocean ridge （MOR） and late suprasubduction zone （SSZ）. zone

关 键 词：高铬型铬铁矿 构造背景 杰莎蛇绿岩 雅鲁藏布江缝合带 

分 类 号：P618.3[天文地球—矿床学]