内蒙古阿拉善右旗塔木素地区三叠纪正长花岗岩成因及构造环境分析

Rock Genesis and Tectonic Environmental Analysis of the Trias Syenogranites From Tamusu Area, Inner Mongolia

塔木素地区三叠纪正长花岗岩岩石化学特征显示其总体呈富硅、碱,高FeOT/MgO比值和10 000×Ga/Al值,贫钙、镁的特征,属准铝质-弱过铝质、高钾钙碱性系列-钾玄岩系列;轻重稀土分馏明显,Eu负异常明显,稀土曲线右倾,属轻稀土富集型;微量元素表现出Zr、Hf、K元素相对富集,而Rb、Sr、Nb、Ta、U、Ti、Cr、Co、Ni元素亏损;同时具有较高的Y/Nb和Rb/Nb值,显示A2型花岗岩的特征。结合相关花岗岩构造图解分析,塔木素三叠纪正长花岗岩为在大陆边缘正常岩浆弧上,由地壳重熔而形成的增生于大陆边缘上的花岗岩,岩浆来源应为壳幔混合。其作为新生地壳的一部分,代表了碰撞晚期或碰撞后地壳增厚、抬升、拉张的构造环境。

The geochemical characteristics of the Trias syenogranites from Tamusu area show that they belong to quasi-alumionous-weakly peralumionous and high-K calc-alkaline granites-shoshonite series with high contents of Si and alkaline and FeOT/MgO and 10000xGa/AI and low contents of Ca and Mg; They indicate that a significant depletion between LREEs and HREEs with a obviously negative Eu anomaly , which belong to richness in LREEs; The elements such as Rb, Sr, Nb, Ta, U, Ti, Cr, Co, Ni are poor and other elements such as Zr, Hf, K are rich .These rocks also have high Y/Nb and Rb/Nb, implying the aluminous A2-type granite. Combined with related the tectonic diagrams of granite, the Trias syenogranites from Tamusu area is a granite which is formed by remelting of the crust and hyperplasiaed on the normal magma arc of the continental margin, whose magma source should be mixed with crust and mantle. As a part of the new crust, it represents the tectonic environment of crust thickening, uplift and tension in the late collsion or after collision.