新疆磁海超大型铁矿区基性岩及其成矿背景指示

新疆磁海超大型铁矿区基性岩与铁成矿关系密切,是认识大规模铁成矿及其背景的关键.磁海铁矿区基性岩以辉绿岩为主,辉绿岩中断裂-裂隙控制板状铁矿脉群,单颗粒锆石U-Pb法测得206Pb/238U平均年龄为263.8±3.6 Ma(n＝11,MSWD=1.3),与二叠纪塔里木、东天山造山带、北山构造-成矿带等区域基性岩同时代.磁海铁矿区基性岩球粒陨石标准化微量元素蛛网图较平坦,Sr、Ba显示弱富集,Nb略亏损,球粒陨石标准化的REE配分曲线平坦,岩浆起源于亏损软流圈地幔,与其所在区域的北山构造-成矿带、东天山造山带、塔里木等地的基性岩均属碱性-钙碱性系列,它们的微量元素组成相近,岩浆性质相似,成生关系密切.磁海铁矿区基性岩可能是二叠纪地幔柱成因塔里木大火成岩省的组成部分,大规模铁成矿于地幔柱背景,北山构造-成矿带可能是塔里木地幔柱的一枝. 

Basic Igneous Rock in Cihai Giant Iron District,Hami, Xinjiang,and Its Indication to the Metallogenic Setting

The basic igneous rock in Cihai giant iron district has a close relationship with the iron mineralization which is the key to understanding of the larger scale of iron metallization and the metallogenic setting. The diabase is the main basic igneous rock in Cihai iron district,and the platy iron-vein group are hosted by the fault-fissures in diabase; the U-Pb dating of single-grained zircon from diabase yielded an average weighted 206Pb/238U age of 263.8±3.6 Ma (n＝11,MSWD=1.3)which is contemporary with that of the basic igneous rock in Permian Tarim basin,eastern Tianshan orogenic belt and Beishan tectonic-metallogenic belt. The trace elements chondrite-normalized patterns of basic igneous rock in Cihai iron district are relatively flat with Sr,Ba enriched and Nb lost lightly; the REE chondrite-normalized patterns are flat. The content of trace elements and magmatic nature of basic igneous rock in Cihai iron district are similar to that of the basic igneous rocks in Permian Tarim basin,eastern Tianshan orogenic belt and Beishan tectonic-metallogenic belt and they all belong to alkaline-calc-alkaline series with close genetic relationship; the basic igneous magma of Cihai district most possibly originated from asthenospheric mantle. The basic igneous rock in Cihai district is possibly a part of Tarim large igneous provinces formed by Permian mantle plum; and the large scale of iron mineralization are also formed in the setting of mantle plum which is a branch of mantle plum in Tarim basin as Beishan tectonic-metallogenic belt.