祁连山玉石沟橄榄岩岩浆作用的记录和铬铁矿的成因  

The Magmatic Record in the Peridotites from Yushigou,Qilian Orogen and the Petrogenesis of the Ophiolite-Type Chromitites

作　　者：胡振兴[1] 牛耀龄[2,3,4] 刘益[4] 孙文礼[1] 陈硕[3] 李继永[3] 张国瑞[1] 

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [2]Department of Earth Sciences,Durham University, DurhamDH1 3LE,UK [3]中国科学院海洋研究所,山东青岛266071 [4]中国地质大学地球科学与资源学院,北京100083

出　　处：《西北地质》2015年第1期1-15,共15页Northwestern Geology

基　　金：中国地质调查局地质调查项目“新疆北部晚古生代大规模岩浆作用与成矿藕合关系研究”(1212011121092);中国大型-超大型矿床成矿地球动力学背景、过程和定量评价综合研究(1212011220928)

摘　　要：祁连山玉石沟蛇绿岩型铬铁矿是典型的高铬型铬铁矿床。通过对玉石沟铬铁矿和橄榄岩围岩进行原位定距离采样研究表明：全岩高的MgO和低的SiO2含量指示这些蛇纹石化橄榄岩不是简单的部分熔融残余,而是经历了后期的熔体再富集作用。玉石沟近矿橄榄岩尖晶石（Cr#〉65）和铬铁矿尖晶石的矿物包裹体化学特征反映矿体和围岩形成于俯冲带上覆岩石圈地幔。距离矿体由近及远,赋矿围岩尖晶石化学成分（Cr#=43.9～77.2,TiO2=0.06%～0.34%）无规律变化。这说明高铬型铬铁矿体成矿所需铬并非来源于围岩,而是与玻安质熔体渗滤有关。尖晶石含水矿物包裹体仅赋存在玉石沟铬铁矿尖晶石与硅酸盐矿物接触部位附近可能揭示了玉石沟铬铁矿体的成因：成矿铬尖晶石在上侵的含水熔体与周围方辉橄榄岩的反应过程中形成聚集。The origin of ophiolite-type chromites remain poorly understood despite the great effort over the years. We have sampled podiform chromites and its host peridotites at certain intervals in Yushigou ophiolite, which is well-known for its high-Cr chromites in the Early Paleozoic Qilian suture zone. The very high MgO and low SiO2 content of these serpentinized peridotites reflect that they are too depleted to be residues of partial melting. Both the chromites and peridotites may have undergone multi-processes of tites, their spinels have very high Cr# melt refertilization. Compared with global abyssal perido- （〉65）. Furthermore, the uniform chemical characteristics of chromite-hosted silicate mineral inclusions suggest that the orebody may have formed in the suprasubduction zones setting. With irregular changes of spatial distribution in Cr# from 77.2 to 43.9 and TiO2 from 0.34 % to 0.06 %, the spinels in host peridotites show that formation of the high-Cr chromites have a boninitic melt affinity instead of originating from the host peridotites. The hydrous mineral inclusions only occur near the outer edge of chromian spinels and silicate minerals may provide evidence for our hypothesis： chromite ore formation results from interaction of hydrous melt with harzburgitic ambience during ascent.

关 键 词：豆荚状铬铁矿 包裹体 玻安质熔体 水 玉石沟 

分 类 号：P511.4[天文地球—地质学]