西藏玛依岗日地区辉长岩地球化学特征及其构造意义
Geochemical Characteristics and Tectonic Implications of Gabbro in Mayigangri Area, Tibet

摘要： 西藏玛依岗日地区侵入脉岩为辉长岩，通过采集辉长岩样品，观察显微照片，并进行主量元素、微量元素和稀土元素含量测试。结果表明：Na2O与K2O含量变化范围不大，全碱(K2O+Na2O)含量为186%～411%，样品K2O/Na2O值的范围为025～066。岩石富集轻稀土、亏损重稀土，铕无正负异常。总体富集Hf、La、Nd、Ti，亏损P、Yb、Y等元素。地球化学特征表明其形成于陆内裂谷环境，岩浆来源于富集地幔，受到硅铝质地壳物质的混染。结合辉长岩围岩为晚石炭世—早二叠世浅变质岩系以及早二叠世晚期之后的地层中不发育岩墙群的事实，而且根据前人对藏北羌塘南部地区基性岩墙群为晚石炭世—早二叠世的年龄约束，推断研究区内南北向辉长岩可能为古特提斯洋拉张初期的产物。
Abstract: The intrusive dikes in Mayigangri area of Tibet are gabbros. Based on the micrograph of the gabbrosamples, the contents of major elements, trace elements and REEs are measured. The results show that the rocks are characterized by an enrichment of LREE, and a depletion of HREE. There is no positive or negative Eu anomaly. The gabbro are enriched in Hf, La, Nd and Ti, and are depleted in P, Yb, Y and other elements. The geochemical features indicate that the gabbros are generated in an intracontinental rift environment; and the magma is derived from enriched mantle with a contamination of salic crust materials. Combined with the fact that gabbro surrounding rocks are Late Paleozoic low metamorphic rock series and undeveloped dike swarms in strata after late Early Permian, and based on the age restrictions that the basic dike swarms in south part of northern Qiangtang is formed from Late Carboniferous to Early Permian by the predecessors, it is deduced that the gabbro is the product that paleoTethys ocean in this region opened initially