中天山巴伦台一带志留纪花岗质侵入体地球化学特征及意义

Geochemistry Characteristics of Silurian Granitoids from Baluntai Area in Central Mountains,and Its Tectonic Significance

新疆中天山巴伦台地区广泛分布花岗质侵入体,通过对乌瓦门断裂北侧石英闪长岩进行LA-ICP-MS锆石U-Pb定年,获得岩体侵位年龄(441.7±2.6)Ma(n=23,MSWD=0.02),属早志留世。岩石地球化学特征表明,该期侵入岩主要为一套过铝质钙碱性系列岩石,稀土元素分布图呈右倾模式,具较高La_N/Yb_N值(7.85~22.90)、Eu负异常(δEu=0.24~0.82)。微量元素蛛网图上岩石总体富集大离子亲石元素K,Rb,Cs等和高场强元素Th,U,Zr,Hf,亏损大离子亲石元素Ba,Sr和高场强元素Nb,Ta,Ti,表明巴伦台地区早志留世花岗质侵入体形成于火山弧环境。综上认为,南天山洋盆向北的俯冲作用不晚于早志留世,为重建中天山构造演化提供了依据。

Granitoids widely distributed in Baluntai area,Central Tianshan Mountain.The LA-ICP-MS age of Monzogranite which was located in north of Wuwamen fault is(441.7±2.6) Ma(MSWD=0.02,n=23).Geochemistry results show that major elements are belong to peraluminous calc-alkaline rocks series,and REEs are characterized by right-type distribution patterns and higher La_N/Yb_N(7.85~22.90) with negative Eu anomaly(δEu=0.24~0.82).In addition,they display LILE enrichment of K,Rb and Cs,but depleted of Ba and Sr,HFSE depletion(Th,U,Zr and Hf),obviously Nb and Ta negative anomalies,and slight Ti depletion.The geochemical characteristics show that early Silurian Granitoids have characteristics of volcanic arc Granites.In conclusion,we believe that the identification of early Silurian arc magmatism in Baluntai area of central Tianshan Mountains indicating the subduction of South Tianshan oceanic basin to the north no later than the Early Silurian.This provides a basis for the reconstruction of the tectonic evolution of the Tianshan Mountains.