西藏班公湖-怒江缝合带中段切里湖豆荚状铬铁矿地球化学特征及构造意义  

Geochemical characteristics and tectonic significance of podiform chromitite in the Qielihu in the middle segment of the Bangong-Nujiang suture,Tibet

作　　者：闫金禹 熊发挥[1,2] 徐向珍 张承杰[3] 卢雨潇 何兰芳 王天泽 杨经绥[1,7] YAN Jinyu;XIONG Fahui;XU Xiangzhen;ZHANG Chengjie;LU Yuxiao;HE Lanfang;WANG Tianze;YANG Jingsui(CARMA(Center for Advanced Research on Mantle),Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou,Guangdong511458,China;The Second Geo-Exploration Institute of CMGB,Fuzhou,Fujian 350108,China;CNPC XDEC Geological Research Institute,Kelamayi,Xijiang834000,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing100029,China;No.5 Geological Survey Party,Tibet Autonomous Region Geological and Mineral Exploration and Development Bureau,Golumd,Qinghai 816099,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing,Jiangsu 210023,China)

机构地区：[1]地幔研究中心,自然资源部深地动力学重点实验室,中国地质科学院地质研究所,北京100037 [2]南方海洋科学与工程广东省实验室(广州),广东广州511458 [3]中国冶金地质总局第二地质勘查院,福建福州350108 [4]中国石油西部钻探地质研究院,新疆克拉玛依,834000 [5]中国科学院地质与地球物理研究所,矿产资源研究重点实验室,北京100029 [6]西藏自治区地质矿产勘查开发局第五地质大队,青海格尔木816099 [7]南京大学地球科学与工程学院,江苏南京210023

出　　处：《地质学报》2022年第12期4294-4311,共18页Acta Geologica Sinica

基　　金：青藏高原第二次科学考察专项(编号2019QZKK0801);国家自然科学基金项目(编号92062215,42172069,41720104009);中国地质调查局工作项目(编号DD20221817,DD20221630);自然资源部深地动力学重点实验室自主研究课题(编号J1901-28)联合资助成果。

摘　　要：切里湖蛇绿岩出露于班公湖-怒江缝合带中段,蕴含较为丰富的铬铁矿资源。蛇绿岩主要由蚀变地幔橄榄岩、辉长岩和辉绿岩组成,铬铁矿矿体呈透镜状分布在地幔橄榄岩内部。切里湖地幔橄榄岩橄榄石Fo(90.06~90.74)和铬尖晶石Cr#值(67.45~85.42)较高,全岩富集MgO、LREE和大离子亲石元素(LILEs,如Rb、Ba等),亏损Al_(2)O_(3)、CaO、高场强元素(HFSE,如Th、Ta、Ce、Nb)和PPGE(Rh、Pt、Pd),这些特征与缝合带其他地幔橄榄岩相似,指示它们具有深海地幔橄榄岩及弧前地幔橄榄岩特征,经历了早期高程度熔体抽取和晚期熔体交代过程。切里湖铬铁矿矿石具有致密块状和浸染状构造,包含磁铁矿、黄铜矿、方铅矿等多种包裹体。铬铁矿Cr#值为65.5~75.8,Mg#值为64.89~76.04,平衡熔体显示出玻安质熔体的亲缘性。与地幔橄榄岩相比,切里湖铬铁矿的IPGE与PPGE分馏更加明显,IPGE更加富集。地幔橄榄岩和铬铁矿Δlgf_(O2)(FMQ)的相近,介于-1.97~0.69之间,表明两者起源于相同的构造背景。对比其他蛇绿岩,认为班公湖-怒江缝合带的蛇绿岩起源于大洋中脊环境,后受到了俯冲带的影响,显示多阶段演化过程。Qielihu ophiolite is located to the middle part of the Bangong-Nujiang suture which is rich in chromitite resources.Qielihu ophiolite is mainly composed of altered mantle peridotite,gabbro and diabase,and chromite orebodies are lenticular in the interior of mantle peridotite.The olivine Fo(90.06~90.74)and chromite Cr#(67.45~85.42)of the mantle peridotite from the Qielihu are relatively high,the whole rock is rich in MgO,LREE and large ion lithophile elements(such as Rb,Ba,etc.),and depleted in Al_(2)O_(3),CaO,high field strength elements(such as Th,Ta,Ce,Nb)and PPGE(Rh,Pt,Pd).These characteristics are similar to other mantle peridotites in the Bangong-Nujiang suture zone,indicating that they have the characteristics of Abyssal mantle peridotite and Forearc mantle peridotite.Meantime,it has gone through the process of early high degree melt extraction and late melt metasomatism.The Qielihu chromitite ore has a dense massive and disseminated structure and contains many kinds of inclusions such as spinel,chalcopyrite,galena and so on.The Cr#value of chromitite is 65.5~75.8and the Mg#value is 64.89~76.04.The equilibrium melt shows the affinity of vitreous melt.Compared with mantle peridotite,the IPGE and PPGE fractionation of Qielihu chromitite is more obvious.TheΔlgf_(O2)(FMQ)values of mantle peridotite and chromitite are similar,ranging from-1.97to 0.69,indicating that they are derived from the same tectonic setting.Compared with other ophiolites,it is considered that the ophiolite in the Bangong-Nujiang suture originated from the mid-ocean ridge environment and its formation experienced multi-stage evolution.

关 键 词：班公湖-怒江缝合带 地幔橄榄岩 全岩地球化学 蛇绿岩 铬铁矿 切里湖 

分 类 号：P618.3[天文地球—矿床学]