西藏丁青蛇绿岩高铬型和高铝型铬铁矿的矿物化学和矿物包裹体特征及其对构造环境的指示意义  

Characteristics of mineral chemistry and inclusions in high-chromium type and high-aluminum type chromitites from the Dingqing ophiolite in Tibet and their critical implication for tectonic setting

作　　者：李观龙 刘飞[1] 朱昕洋 刘朋东 杨经绥[1,3] LI GuanLong;LIU Fei;ZHU XinYang;LIU PengDong;YANG JingSui(SinoProbe Laboratory,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]自然资源部深地科学与探测技术实验室,中国地质科学院地质研究所,北京100037 [2]中国地质大学(武汉)地球科学学院,武汉430074 [3]南京大学地球科学与工程学院,南京210023

出　　处：《岩石学报》2024年第12期3753-3780,共28页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(92062215、42472094);中国地质调查局地质调查项目(DD20242124、DD20221630、DD20240075、DD20230340);山东地勘局七队科研项目(QDKF-YB202301)联合资助。

摘　　要：班公湖-怒江蛇绿岩带是目前我国铬铁矿找矿最有潜力的成矿带之一,在我国铬铁矿找矿与铬资源供应中具有极其重要的地位。丁青蛇绿岩作为班怒带中出露面积最大和铬铁矿矿点最多的岩体,同时发育高铬和高铝两种类型的铬铁矿。本研究以丁青蛇绿岩中的高铬型和高铝型铬铁矿矿石及其围岩地幔橄榄岩为研究对象,开展了详细的岩石学、矿物包裹体和矿物化学等分析与研究工作。研究显示,高铬型和高铝型铬铁矿矿石与围岩纯橄岩和方辉橄榄岩的铬尖晶石的矿物化学、包裹体类型和组合及其成分等特征均表现出显著的不同。高铬型铬铁矿矿石中铬尖晶石的Cr^(#)值为70.51~73.51,NiO在0.05%~0.16%之间,TiO_(2)=0.05%~0.17%。高铝型铬铁矿矿石中铬尖晶石的Cr^(#)值为30.84~31.87,NiO=0.15%~0.27%,TiO_(2)=0.14%~0.28%。高铬型铬铁矿矿石中铬尖晶石的矿物包裹体以角闪石和单斜辉石为主,高铝型铬铁矿矿石中的铬尖晶石则以橄榄石和角闪石与单斜辉石的多晶矿物包裹体为主。通过铬尖晶石主量元素计算成矿母岩浆的组成,高铬型铬铁矿矿石及其围岩纯橄岩中铬尖晶石的母岩浆组成反映了弧前玻安岩的地球化学特征,而高铝型铬铁矿矿石及其围岩纯橄岩中铬尖晶石的母岩浆组成表现出拉斑玄武岩特征。高铬型铬铁矿矿石及其围岩地幔橄榄岩的矿物化学和矿物包裹体数据指示其形成于弧前的构造环境,而高铝型铬铁矿形成于俯冲初始阶段的弧前环境。结合丁青地幔橄榄岩具有较高的部分融熔程度和大陆岩石圈地幔的Re-Os同位素特征,暗示丁青蛇绿岩可能形成于陆缘弧前环境。Bangong Lake-Nujiang suture zone(BNSZ)is currently one of the most chromite-enriched mineralization belts in China.It holds an extremely important position in chromitite exploration and chromium resource supply in our country.The Dingqing ophiolite,as the 550km 2 largest area of ophiolite in the BNSZ with the largest number of chromitite occurrences,is characterized by the simultaneous development of high-chromium type chromitite(HCT)and high-aluminum type chromitite(HAT).This study focuses on the HCT and HAT and their wall-rock peridotites in the Dingqing ophiolite,we conduct detailed research on petrographic description,mineral contents,mineral inclusions and their geochemical compositions.The results show that the mineral chemistry,inclusion assemblages and their geochemical compositions of Cr-spinel in the HCT and HAT as well as their wall rocks are obviously different.The Cr#value of Cr-spinel in HCT ranges from 70.51 to 73.51,NiO=0.05%~0.16%,TiO_(2)=0.05%~0.17%.The mineral inclusions in Cr-spinel are mainly amphibole and clinopyroxene.In contract,the Cr#value of Cr-spinel in HAT ranges from 30.84 to 31.87,NiO=0.15%~0.27%,TiO_(2)=0.14%~0.28%.Their mineral inclusions in Cr-spinel are mainly olivine and polycrystalline assemblage of amphibole and clinopyroxene.The calculated parent magma compositions of HCT and its wall-rock peridotites geochemically reflect the forearc type of boninite features,while the HAT counterparts exhibit the geochemical characteristics of tholeiite basalt.These data combined with extremely high degree of partial melting of wall-rock peridotites with Re-Os isotope characteristics of subcontinental lithospheric mantle indicate that the HCT and HAT in the Dingqing ophiolite formed at different stages in a forearc setting close to continent.

关 键 词：班公湖-怒江缝合带 丁青蛇绿岩 高铬型和高铝型铬铁矿 矿物包裹体 弧前环境 

分 类 号：P578.46[天文地球—矿物学] P588.125[天文地球—地质学]