东昆仑清水泉蛇纹岩中铬铁矿特征及其构造意义  

Characteristics and tectonic significance of chromites from Qingshuiquan serpentinite of East Kunlun,Northwest China

作　　者：冯惠彬 孟繁聪[2] 李胜荣[1] 贾丽辉[2] 

机构地区：[1]中国地质大学、地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质科学院地质研究所、大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石学报》2015年第8期2129-2144,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272052);中国地质调查局项目(1212010918003、1212011120158、12120114080101、12120115027001)联合资助

摘　　要：东昆仑造山带清水泉中超基性岩已蚀变为蛇纹岩,很难对其性质和形成环境进行判断,但蛇纹岩中存在的浸染状和条带状铬铁矿有助于识别超基性岩的性质及形成过程。显微结构和电子探针分析结果显示部分铬铁矿具环带结构,核部为富Al贫Fe的铝铬铁矿,Cr2O3为36%~44%,Al2O3为24%~28%,Ti O2含量很低（〈0.1%）,Fe O为15%~24%,而Fe2O3含量为0.6%~3.0%,Cr#为0.47~0.56,Mg#为0.45~0.62,Fe2＋#变化于0.38~0.55,显示出蛇绿岩的特性,由此推测其寄主岩石——方辉橄榄岩属于蛇绿岩成员。核部铝铬铁矿结晶温度平均约为1387℃,结晶压力平均为2.9GPa,推断其形成深度约为88km,相当于软流圈位置。核部铝铬铁矿Cr#-Mg#,Cr#-Ti O2以及Ti O2-Al2O3的关系特征显示其寄主岩石——方辉橄榄岩可能产自俯冲带环境中的弧前位置。The disseminated and banded chromites in the serpentinized ultrabasic rocks in the Qingshuiquan area,Eastern Kunlun Mountains,are helpful to clarify the characteristics and evolutionary process of the rocks. The result of electron microprobe analysis shows that some chromites have zoned texture,with rich Al but poor Fe in the core. The geochemical characteristics of the core of chromites,with Cr2O336% ~ 44%,Al2O324% ~ 28%,Ti O2 less than 0. 1%,Fe O 15% ~ 24%,Fe2O30. 6% ~ 3. 0%,Cr#0. 47~ 0. 56,Mg#0. 45 ~ 0. 62,Fe2 ＋ #0. 38 ~ 0. 55,are in accord with that of ophiolites,which indicates that the harzburgite,host rock of chromites,may be a member of ophiolites. Moreover,the crystallized temperature and pressure of the chromite are estimated to be1387℃ and 2. 9GPa on average,respectively,with a formation depth of about 88 km,which is similar to that of the asthenosphere. The discriminate diagrams,including Cr#-Mg#,Cr#-TiO2 and TiO2-Al2O3 diagrams,reveal that the host rock of chromites was formed in the depleted fore-arc setting of supra-subduction zone.

关 键 词：铬铁矿 蛇绿岩 蛇纹岩 构造环境 东昆仑 

分 类 号：P575.1[天文地球—矿物学] P578.46[天文地球—地质学]