新疆中天山南缘代京却可却花岗岩锆石U-Pb年龄及地球化学特征

摘要

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.围绕中天山代京却可却花岗岩进行锆石LA-ICP-MS U-Pb定年获得岩浆结晶年龄为(469.7±4.9) Ma,时代为中奥陶世.花岗岩SiO2含量69.91％～74.4％,具低TiO2(0.1％～0.27％)和高Al2O3(13.02％～13.68％)特征.轻重稀土元素分馏明显,富集轻稀土元素,Eu负异常(δEu=0.69～0.81).岩石地球化学研究表明,花岗岩富集大离子亲石元素Th,Rb,K,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定年结果及区域地质背景,认为代京却可却花岗岩可能是中天山南缘大洋俯冲消减作用产物,该区大洋俯冲消减至少在中奥陶世前开始.%Chinese Central Tianshan is located in the central part of the Tianshan Orogenic Belt,is of significant importance for understanding the tectonic evolution,origination and continental growth of the Central Asian Orogenic Belt.This paper focuses on tectonic implications of granitoid intrusions from the Dajingquekeque at the Southern margin of the Central Tianshan Mountain.Granite intruded at (469.744.9) Ma based on the dating results of zircon U-Pb geochromology,it suggested that the granite erupted in Middle Ordovician Epoch.The granite is characterized by SiO2 content from 69.91％～74.4％,low TiO2 (0.1％～0.27％) 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 negative Eu anomaly (δEu=0.69～ 0.81).Geochemical characteristic of metamorphism andesite suggest that it shows island-arc volcanic chatacteristics,being enriched in LILE such as Th,Rb,K and depleted in HFSE such as Nb,Ta,Ti,P.In combination with the result of LAICP-MS zircon U-Pb dating and regional geological setting,we suggest that the Dajingquekeque granite was resulted from the ocean subduction in the Southern margin of the Central Tianshan Mountain,the oceanic subduction began at least in the Middle Ord ovician Epoch.