阿尔金盖里克片麻岩地球化学特征及构造环境分析

Geochemical Characteristics and Tectonic Environment Analysis of the Proterozoic Gneiss in Gailike ,Altun

阿尔金曼特里克地区元古代盖里克片麻岩锆石U-Pb年龄为927.1±5.5Ma。岩石SiO2含量为62.02%~68.89%,Al2O3含量为14.08%~16.54%,TFe2O3含量为3.73%~7.44%,CaO含量为1.77%~3.81%,TiO2、MnO、P2O5含量均小于1%;(Na2O+K2O)含量为5.32%~7.06%。岩石的碱度率指数AR为1.80~2.53,显示富铝的特征,岩石的Mg#值为39.08~57.44,里特曼指数σ为1.13~1.87,说明盖里克片麻岩岩体具有钙碱性系列岩石的特征。岩石微量元素富集Rb、Th、K、Nd等元素,相较亏损高场强元素,如Zr、Hf、Nb、Ta等,显著亏损Ba、Sr、P、Ti等元素,说明该岩体具有大陆碰撞型花岗岩相应的元素丰度特征;稀土元素中岩石轻稀土分馏较明显,重稀土分馏表现相对较弱,显示LREE富集、HREE略显平坦的右倾型分布特征。地球化学特征显示盖里克片麻岩的岩浆主要来源于下地壳中角闪岩相基性岩类(变玄武岩)的部分熔融,形成于俯冲-同碰撞构造转折环境,结合年龄数据说明其可能是阿尔金南缘Rodinia超大陆碰撞事件的反应,为新元古代阿尔金造山带的构造演化提供了有力的证据。

The LA-ICP-MS zircon U-Pb age of the Proterozoic Gailike gneiss in the Altun Mantelike area is 927.1+5.5 Ma. The content of SiO 2 is 62.02%~68.89%, Al 2O 3 is 14.08%~16.54%, TFe 2O 3 is 3.73%~7.44%, CaO is 1.77%~3.81% in rocks, TiO 2、MnO、P 2O 5 less than 1% and (Na 2O+ K 2O) is 5.32%~7.06%. Calculated rock AR is 1.80~2.53, showing the characteristics of aluminium-rich rocks. Mg # value of rocks ranges from 39.08 to 57.44, and σ ranges from 1.80 to 2.53, indicating that the rock body has the genetic characteristics of calc-alkaline series rocks. Trace elements in rocks enrich Rb, Th, K, Nd, etc. Relatively depleted HISF, such as Zr、Hf、Nb、 Ta、Ba、Sr、P、Ti, the results show that the rocks have the corresponding element abundance characteristics of typical continental collisional granites, and the fractionation of light rare earth elements in the rocks is obvious, while the fractionation of heavy rare earth elements is relatively weak, indicating that LREE enrichment and HREE have a slightly flat right-leaning distribution characteristics. Geochemical characteristics show that the magma of the Gelik gneiss originated mainly from partial melting of amphibolite facies basic rocks (metabasalts) in the lower crust and formed in a Subduction-Collision tectonic turning environment. Combined with the dating data, it is suggested that the magma may be the reaction of the Rodinia supercontinent convergence event on the southern margin of Altun, which provides strong evidence for the Neoproterozoic tectonic evolution of the Altun orogenic belt.