内蒙古贺根山蛇绿岩中铬铁矿特征及大地构造环境  

Characteristics and Tectonic Environment of Chromites from the Hegenshan Ophiolite in Inner Mongolia

作　　者：王成 任利民[2] 张晓军[3] 余国飞 田江涛 李大海 

机构地区：[1]新疆地质调查院,新疆乌鲁木齐830000 [2]中国地质大学(武汉)地球科学学院,武汉430074 [3]中国地质大学(武汉)资源学院,武汉430074 [4]湖北省地质局第一地质大队,湖北黄石435100

出　　处：《矿物岩石地球化学通报》2018年第1期139-148,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：中国地质调查局地质调查项目(1212011220448);新疆区域地质调查片区总结与服务产品开发项目(DD20160345-04)

摘　　要：为探讨内蒙古贺根山蛇绿岩形成的物化条件和大地构造环境,选取贺根山未蚀变豆荚状铬铁矿进行矿物学和矿物地球化学分析。结果表明,铬铁矿成分均一,不发育环带结构;铬铁矿中的Cr2O3含量为36.12%~43.77%,Al2O3为22.81%~30.14%,TFeO为12.63%~17.56%,Cr^#为46~56,Mg^#为68~78,Yfe为4~7,Fe^2＋#为22~36,为富铝型铬铁矿,其寄主岩石属于蛇绿岩。铬铁矿结晶温度均为1395℃,结晶压力平均为3.3 GPa,推断其形成深度约为103 km;相对于FMQ缓冲剂的地幔氧逸度为FMQ＋1.03~FMQ＋1.83 lg单位,均值为FMQ＋1.59 lg单位;地幔熔融程度F为20.63%~21.50%,均值为20.93%。推测贺根山铬铁矿原岩橄榄岩单元源区为石榴石二辉橄榄岩,形成于亏损地幔,可能产自俯冲带环境中的洋内弧后盆地环境。In order to discuss the physicochemical condition and tectonic environment for the formation of the ophiolite in Inner Mongolia,unaltered podiform chromites from the Hegenshan ophiolite were chosen to study its mineralogy and mineral geochemistry in this paper.The result shows that podiform chromites,which have no zoned texture,contain general uniform compositions of Cr2O3 varying from 36.12% to 43.77%,Al2O3 varying from 22.81% to 30.14%,and TFe O varying from 12.63% to 17.56%,with Cr^# values of 46-56,Mg^#values of 68-78,Yfe values of 4-7,and Fe^2＋# values of 22-36.They are aluminum-rich chromites hosted in the ophiolite.Moreover,the estimated average temperature and pressure for crystallization of the chromite are 1395 ℃ and 3.3 GPa,respectively,inferring its formation depth of about 103 km,the mantle oxygen fugacities varying from FMQ＋1.03 to FMQ ＋ 1.83 lg units（average FMQ ＋ 1.59 lg units）,and degrees of partial melting of the mantle varying from 20.63% to 21.50%（average 20.93 %）.Therefore,it is inferred that the Hegenshan chromite-hosting peridotite,which could be derived from the garnet lherzolites in the depleted upper mantle,could be formed in the intra-oceanic back-arc basin setting in the subduction zone.

关 键 词：豆荚状铬铁矿 蛇绿岩 洋内弧后盆地 贺根山 内蒙古 

分 类 号：P618.33[天文地球—矿床学]