新疆东准噶尔扎河坝橄榄岩单斜辉石、铬尖晶石地球化学特征及铬铁矿成矿作用
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P618.33

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中国地质调查局项目(DD20190071)和中国地质科学院基本科研业务费项目(JKY201908-01)联合资助。


Geochemistry of clinopyroxene and chrome spinel in the Zhaheba peridotite, Eastern Junggar, Xinjiang, China and its chromitite metallogenesis
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    摘要:

    扎河坝蛇绿岩是东准噶尔地区一条重要的蛇绿岩带,主要由橄榄岩、层状辉长岩、玄武岩、斜长花岗岩、硅质岩等组成。其中橄榄岩主要由方辉辉橄岩(方辉橄榄岩)、二辉橄榄岩和少量纯橄岩组成。二辉橄榄岩中的单斜辉石Cr2O3平均1.11%,Al2O3平均4.77%,MgO平均16.99%,CaO平均21.84%,SiO2平均50.00%;铬尖晶石副矿物具有较低的Cr2O3(平均40.35%)、Cr#(平均0.53)和更高的Al2O3(平均24.10%),MgO(平均13.23%)和Mg#(0.62)含量,属高Al型,橄榄岩形成于扎河坝洋扩张时期(MOR环境);块状铬铁矿铬尖晶石各元素含量变化较小:Cr2O3平均55.45%,Al2O3平均10.88%,MgO平均11.98%和Mg#为0.60,属SSZ背景高Cr型铬铁矿。二辉橄榄岩单斜辉石具有典型的熔融残余结构和熔-岩反应结构,斜方辉石保留绢石化假晶和部分未蚀变的辉石残余体(主要是顽火辉石),铬尖晶石副矿物具有熔蚀特征。单斜辉石的熔融残余结构是含铬矿物熔融、释放铬的一种表现,是橄榄岩部分熔融程度升高,向更富镁方向演化的结构标志,但可能对富Cr型铬铁矿的形成贡献有限。橄榄岩存在熔-岩反应新生的单斜辉石、橄榄石及结构标志。熔-岩反应过程中流体、挥发分的作用不可忽视。文章还探讨了铬铁矿Cr#、Mg#和Al2O3含量差异与蛇绿岩形成的构造背景关系及影响因素。卡拉麦里洋壳俯冲和地幔对流循环使扎河坝早期形成于MOR环境的富Al铬尖晶石富集,形成高Cr块状铬铁矿。

    Abstract:

    Zhaheba ophiolite is a significant ophiolite complex in Eastern Junggar, consisting mainly of peridiotite, basalt, layered gabbro, plagiogranite and chert. Among them, the peridiotite is mainly composed of harzburgite, herzolite, and minor dunite. The average contents of clinopyroxene in herzolite are Cr2O3 1.11%, Al2O3 4.77%, MgO 16.99%, CaO 21.84%, SiO2 50.00%, and the accessory mineral chromium spinel falling within the high-Al types has lower average contents Cr2O3 40.35%、Cr# 0.53 but higher Al2O3 24.10%, MgO 13.23% and Mg#(0.62),which indicate that it was formed during the extension of Zhaheba ocean in MOR environment. While the element contents of chrome spinels in massive chromites changes little with average contents of Cr2O3 55.45%、Al2O3 10.88%, MgO 11.98% and Mg# 0.60, which fall in high-Cr type fields and belong to SSZ type of chromites. Clinopyroxenes in herzolite is characterized by typical structures of melted residue and melt-rock reaction, and orthopyroxene in harzburgite kept bastitic pseudomorphs and unaltered enstatites, but chrome spinel accessory minerals show corrosion features. The melting residual structure of monocline is a manifestation of the melting and chromium release of chromium-bearing minerals, and also a structural indicator of the partial melting degree of peridotite increasing and the evolution towards more magnesium rich direction, which may have limited contribution to the formation of Cr-rich chromite. The peridotite contains monoclinopyroxene, olivine and textures newly generated from melt-rock reaction. The role of fluid and volatiles in the melt-rock reaction cannot be ignored. Based on the above studies, the relationship among the content differences of Cr#、Mg# and Al2O3 of chromite and tectonic settings of ophiolite, and its influence factors are discussed. It is concluded that mantle convection and subduction of Kalamaili ocean led to the enrichment of the high-Al chrome spinels in MOR environment and forming of massive chromites.

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王召林,孟贵祥,汤贺军,袁璐璐,杨竹森,肖艳东. 新疆东准噶尔扎河坝橄榄岩单斜辉石、铬尖晶石地球化学特征及铬铁矿成矿作用[J]. 中国地质, 2021, 48(2): 477-494.
WANG Zhaolin, MENG Guixiang, TANG Hejun, YUAN Lulu, YANG Zhusen, XIAO Yandong. Geochemistry of clinopyroxene and chrome spinel in the Zhaheba peridotite, Eastern Junggar, Xinjiang, China and its chromitite metallogenesis[J]. Geology in China, 2021, 48(2): 477-494(in Chinese with English abstract).

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  • 收稿日期:2019-12-04
  • 最后修改日期:2020-02-18
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  • 在线发布日期: 2021-05-06
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