新疆库鲁克塔格西段泥盆纪二长花岗岩年龄、地球化学特征及其构造意义

Geochemistry and geochronology of monzogranites in Kuruktag of Xinjiang and their tectonic implications

通过岩石学、地球化学、锆石U-Pb定年分析了库鲁克塔格西段的2处二长花岗岩体的岩体特征、成因及其地质意义。主量和微量元素分析结果表明,岩体高硅、富钾、偏铝,低磷、低钛,铝饱和指数(A/CNK)分别为0.83～0.97、1.09～1.12,富集大离子亲石元素Rb、K、Ba,亏损高场强元素Ta、Nb、Ti、P,并具有Eu的负异常,体现了火山岛弧花岗岩的地球化学特征,应为高钾钙碱性I型花岗岩,形成于俯冲环境。锆石LA-ICP-MS定年分别获得399.9Ma±1.5Ma及400.6Ma±1.6Ma的年龄,属早泥盆世。对比前人对塔里木北缘岩浆活动的研究成果,笔者认为岩体成因为洋壳向陆壳俯冲的过程中温度升高、脱水使地壳熔融形成长英质岩浆,同时有部分地幔成分的加入,该岩浆后期侵位形成本区的花岗岩体。岩体应形成于俯冲消减的构造环境中,表征南天山洋泥盆纪时期存在向南俯冲。

Geochemistry and geochronogy of the monzogranites from Kuruktag in Xinjiang were studied in this paper. Major elements and trace elements analyses show that the granites have high SiO2, K2O, but relatively low P205 ,TiO2, MgO. The A/CNK ratios in a granite body vary from 0.83 to 0.97 and in another granite body vary from 1.09 to 1.12, suggesting that they belong to high-K calc-alkaline 1-type granite. The granites are relatively enriched in such LILEs as Rb, K and Ba whereas depleted in such HFSEs as Ta, Nb, Ti and P, with Eu anomalies （gEu=0.16-0.18）, thus considered to be the magrnatic arc granites formed in a tectonic environment. Zircon LA-ICP-MS dating yielded the formation ages of 399.9Ma±1.5Ma and 400.6Ma±1.6Ma,which indicate that the plutons were formed in Devonian. In combination with regional geological settings, the authors conclude that the formation of the Kuruktag monzogranites had close relationship with the arc-type magrnatic rocks, and probably resulted from the partial melting of crustal rocks in the active continental margin caused by the plate subducdon.