新疆东昆仑西段库拉甫河岩组火山岩地球化学特征及锆石U-Pb年龄

Volcanic rock geochemical characteristics and zircon U-Pb age of the Kulapuhe Formation-complex in the west of East Kunlun Mountains, Xinjiang

对东昆仑西段库拉甫河岩组火山岩地球化学进行研究,结果显示,主量元素MgO、FeO含量较高,TiO2和K2O含量分别为1.12%、0.63%,与岛弧拉斑玄武岩(0.84%、0.43%)接近;微量元素具有Sr富集,高场强元素Nb、Ta略亏损,P无明显分馏或未分馏的特征,稀土元素球粒陨石标准化配分曲线显示良好的同源性(配分曲线变化规律近似一致),且与富集型洋脊玄武岩配分趋势一致。结合构造环境判别,认为其形成于岛弧环境,具有岛弧拉斑玄武岩的特征,来源于与岛弧相关的富集地幔。利用锆石U-Pb测年获得2组年龄,其中一组年龄为688.7±5.1Ma,代表捕获晶年龄,另一组年龄483.4±3.3Ma为结晶年龄,代表玄武岩的形成年龄,属于早奥陶世。结合其构造环境、岩石地球化学特征和年龄数据,认为其是原特提斯洋俯冲消减环境下的产物,且原特提斯洋俯冲至少持续到早奥陶世。

In this paper, the authors conducted the study of volcanic rock geochemistry of the Kulapuheyan Formation-complex in the western part of East Kunlun Mountains. The results show that the values of MgO and FeO are1.12% and 0.63%, respectively, the values of TiO2 and K2O are close to the value of island-arc tholeiite (0.84%, 0.43%, respectively), the distribution of trace elements shows enrichment of Sr, slight depletion of HFSE Nb and Ta, and no significant fractionation or no fractionation of P, with rare earth pellet meteorite distribution curve showing good homologous nature (similar distribution curve variations). And it is consistent with the distribution trend of E-MORB. It is concluded that it was in an island arc environment and had the characteristics of island- arc tholeiite. It was derived from island-related enrichment mantle. The 688.7±5.1Ma represents the age of the captured crystal, and 483.4±3.3Ma is the age of the representative age of the basalts, and belongs to the Early Ordovician. In combination with its tectonic setting, geochemical characteristics and chronology, the authors hold that it was produced by the subtraction of the original Tethys Ocean subduction, and the original Tethys ocean subducted continuously at least until the Early Ordovician.