柴北缘夏日达乌铌钽矿区花岗岩地球化学特征及地质意义

Geochemical Characteristics and Geological Significance of Granite in Xiaridawu Niobium-Tantalum Mining Area,Northern Margin of Qaidam Basin

柴北缘夏日达乌铌钽矿区分布有大量早古生代花岗岩,剖析花岗岩的岩浆来源、形成机制和构造环境,对于揭示柴北缘陆壳的形成与演化机制具有重要作用。对柴北缘夏日达乌铌钽矿区花岗岩进行了岩石学和地球化学特征分析,结果表明:夏日达乌地区黑云母花岗斑岩主量元素具有高硅、高钾、富铝以及低镁、贫锰、少钛的特征;富集轻稀土元素,相对亏损重稀土元素,REE球粒陨石标准化配分曲线呈“V”字形分布,具有明显负Eu异常;相对富集大离子亲石元素,相对亏损高场强元素。岩石成因属于高分异S型过铝质花岗岩,其中物源主要由地壳物质发生低温熔融所提供,不排除地幔物质的混染;推断花岗岩形成于碰撞造山向板内过渡的碰撞构造环境。

The northern margin of the Qaidam Basin is located in the north of the Qaidam Basin and the south of the Qilian orogenic belt,and in the Qinling-Qilian-Kunlun orogenic belt with strong tectonic-magmatic activity.It is one of the hot areas of geological research in recent years.A large number of early Paleozoic granites are distributed in the Xiaridawu niobium-tantalum mining area in the northern margin of the Qaidam Basin.The analysis of the magma source,formation mechanism and tectonic environment of granites plays an important role in revealing the formation mechanism and tectonic environment of granites,which also plays an important role in revealing the formation and evolution mechanism of continental crust in the northern margin of the Qaidam Basin.Based on the analysis of petrological and geochemical characteristics of granites in Xiaridawu niobium-tantalum mining area on the northern margin of Qaidam Basin,the magma source,formation mechanism and tectonic environment of granites was analized.It is found that the biotite granite porphyry in the Xiaridawu area has high silicon,high potassium and aluminum,and the other major elements show the characteristics of low magnesium and low manganese,poor phosphorus and titanium.The biotite granite porphyry is enriched in light rare earth elements,while relatively depleted in heavy rare earth elements,REE chondrite-normalized partitioning curve is‘V’shaped distribution,and the negative Eu anomaly is obvious.It is relatively enriched in large ion lithophile elements,relatively depleted in high field strength elements.According to the analysis of related parameters of major,trace and rare earth elements,the granite porphyry in the mining area is a highly differentiated S-type peraluminous granite.In addition to the low-temperature melting of crustal materials,the source is not excluded from the contamination of mantle materials,and there are some separated crystallization products,which has a very favorable effect on the mineralization of niobium and tantalum deposits in this area.According to the tectonic environment discrimination of multiple sets of main elements and trace elements,the granite porphyry in the Xiaridawu niobium-tantalum mining area on the northern margin of Qaidam Basin was formed in the collision tectonic environment of the transition from collision orogenic to intraplate.The study has important geological significance for understanding the genesis,provenance,tectonic environment and prospecting direction of granite in this area.