中天山南缘木斯陶萨拉南地区石英闪长岩锆石年龄及构造意义

Zircon U-Pb Age and Tectonic Implications of Quartz Diorite in the Southern Musitaosala Area,Central Tianshan Terrane,Xinjiang

为确定中天山南缘地区侵入岩的成因和构造背景,并且为南天山洋盆的俯冲时限及俯冲极性提供证据,对中天山南缘木斯陶萨拉南地区的石英闪长岩进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学研究。结果表明,岩石的平均年龄为(309±3.8)Ma,属晚石炭世岩浆活动的产物;岩体由一套钙碱性系列过铝质岩石组成,其稀土元素配分型式为明显的右倾模式,轻稀土强烈富集,重稀土强烈亏损,具有较高的(La/Yb)_N值(8.5～50.31)和较弱的Eu正异常或无异常(δEu为1.01～1.3);微量元素蛛网图显示岩石为大离子亲石元素Ba、Sr、K相对富集,高场强元素Nb、Ta、Ti、P相对亏损。综合分析认为,石英闪长岩应形成于火山弧环境,是幔源岩浆底侵带来的大量热能使晚古生代下地壳物质发生部分熔融的产物,记录了晚石炭世南天山洋向中天山微地块之下的俯冲岩浆活动。

In order to determine the origin and tectonic setting of intrusions in the southern margin of Central Tianshan Terrane,and provide evidence to constrain the timing and direction of the subduction of the South Tianshan Ocean,systematic study on quartz diorite in the southern Musitaosala Area is performed.The intrusion has zircon LA-ICP-MS U-Pb ages(309±3.8)Ma,a product of Carboniferous magmatism.The rocks belong to peraluminous calc-alkaline rocks series and are characterized by LREE enrichment with high(La/Yb)_Nratios(8.5-50.31)and weakly positive Eu anomaly(δEu=1.01-1.3).In addition,they display the enrichment of LILE(Ba,Sr and K)and depletion of HFSE(Nb,P,Ta and Ti).The geochemical characteristics suggest that parental magmas of quartz diorite are the product of partial melting of Late Palaeozoic lower crust due to the underplating of mantle-derived magma.Therefore,the Late carboniferous quartz diorite records northward subduction of South Tianshan ocean beneath the Central Tianshan Terrane.