中天山南缘伊尔根布鲁克石英闪长岩锆石U-Pb年龄和地球化学特征

Zircon U-Pb Age and Geochemical Characteristics of Quartz Diorite in Yiergenbuluke at the Southern Margin of the Centre Tianshan Mountain,Xinjiang

中天山位于天山造山带核心部位,对研究中亚造山带西南段构造演化、块体起源和陆壳生长等具重要意义。本次研究围绕中天山伊尔根布鲁克石英闪长岩展开,锆石LA-ICP-MS U-Pb定年获得岩浆结晶年龄为(313.3±5.7)Ma,成岩时代为晚石炭世。花岗岩SiO_2含量58.13%~66.74%,具低CaO含量3.68%~5.79%和高Al_2O_3含量13.02%~13.68%特征。轻重稀土元素分馏明显,富集轻稀土元素,Eu弱正异常或无异常,δEu=0.95~1.3。岩石地球化学研究表明,花岗岩富集大离子亲石元素Ba,Sr,K和亏损高场强元素Nb,Ta,Ti,P,具火山弧花岗岩特征。结合岩石锆石LA-ICP-MS定年结果和区域地质背景,认为伊尔根布鲁克石英闪长岩可能是中天山南缘大洋俯冲消减作用的产物,该区大洋俯冲消减至少延续到晚石炭世。

Chinese Central Tianshan,located in the central part of the Tianshan Orogenic Belt,is of signigicant importance for understanding the tectonic evolution,origination and continental growth of the Central Asian Orogenic Belt.This paper focuses on tectonic implications of quartz diorite intrusions from the Yiergenbuluke at the Southern margin of the Central Tianshan Mountain.Granite intruded at（313.3±5.7） Ma based on the dating results of zircon U-Pb geochromology,it suggested that the granite erupted in Late Carboniferous Epoch. The granite is characterized by SiO2 content from 58.13% -66.74%,low CaO（3.68-5.79%）and high Al2O3（13.02% -13.68%）.The granite forms a LREE-enriched distribution pattern with a strong contrast between LREE and HREE and the existence of positive or normal Eu anomaly（δEu= 0.95-1.3）.Geochemical characteristic of metamorphism andesite suggest that it shows island-arc volcanic chatacteristics,being enriched in LILE such as Ba,Sr,K and depleted in HFSE such as Nb,Ta,Ti,P.In combination with the result of LA-ICP-MS zircon U-Pb dating and regional geological setting,we suggest that the Yiergenbuluke quartz diorite was resulted from the ocean subduction in the Southern margin of the Centre Tianshan Mountain,the oceanic subduction lasted for the Late Carboniferous Epoch.