古特提斯洋在三叠纪时期沿现今勉略缝合带的闭合,标志着华北板块(NCB)和扬子板块(YZB)的最终拼贴完成.秦岭造山带西段发育印支期花岗岩浆活动,为该地区的成矿作用提供了有利的条件.对这些岩浆岩的形成时代、地化属性、演化、来源等的研究将有助于了解该时期的构造背景及动力学环境.本文以西秦岭北亚带的江里沟复式岩体作为研究对象,通过LA-ICP-MS锆石U-Pb测年、锆石Hf同位素测试和主微量元素分析,对该岩体进行了系统的研究.结果显示:江里沟复式岩体的三种主要岩性为斑状黑云母二长花岗岩、花岗斑岩和细粒花岗岩,加权平均年龄分别为:229.1±1.8Ma (MSWD=0.82)、222.5±1.4Ma(MSWD=0.41)和217.1±1.8Ma(MSWD=1.4),指示该岩体形成于晚三叠世.其地球化学性质具有高硅(SiO2 =72.67％ ～ 77.84％),富碱(K2O+ Na2O=7.67％ ～ 8.75％),弱过铝质(A/CNK=1.01～1.06),高度分异(岩体由早至晚DI及Rb/Sr均升高,DI=88.9 ～95.36,Rb/Sr=1.76～ 12.19),富集Rb、Th、U、Ta、Zr、Hf和HREE元素特点,亏损Ba、Sr、P、Ti等元素;三个侵入体均发育明显负Eu异常(δEu =0.54～0.62、0.26～0.47、0.20～0.60);P2O5含量与SiO2呈明显的负相关关系,而Y的含量反之,综合判定认为,岩体属高分异I型花岗岩.岩石形成温度从早至晚明显降低(平均由786℃至755℃).εHf(t)值少数＜0外,绝大多数介于0.1～4.8之间,相应tDM2=0.95～1.25Ga.综合推断认为,江里沟岩体的原始岩浆是由部分熔融的岩石圈地幔与中新元古代的地壳混合,形成的混合岩浆,后经强烈的结晶分异作用形成江里沟复式岩体.%The Paleo-Tethys Ocean closed along Mianlue Suture in Triassic marked the final closing between North China Block (NCB) and Yangtze Block (YZB).In the western part of Qinling (named "West Qinling" for short),numerous of Indosinian granitiod caused by the strong tectonic-magmatic activity also generated a lot of mineralization in the area.These Indosinian-granites as a probe of their research will help to understand the structure and dynamics in the context of the period.The Jiangligou composite granite,occurred in the north of West Qinling,can be divided into three facies,and was carried out for LA-ICP-MS zircon U-Pb zircon dating,zircon Hf isotope test,the major and trace elements test.The zircon U-Pb dating results show the weighted average age of porphyritic biotite monzonite granite,granite porphyry and fine-grained granite were:229.1 ± 1.8Ma (MSWD =0.82),222.5 ± 1.4Ma (MSWD =0.41) and 217.1 ± 1.8Ma (MSWD =1.4),which indicated Jiangligou composite granite (JCG) was formed in the late middle-late Triassic.Geochemical data shows that:JCG have the features of high silicon (SiO2 =72.67％ ～ 77.84％),alkali-rich (K2O + Na2O =7.67％ ～ 8.75 ％),weakly peraluminous (A/CNK =1.01 ～ 1.06),high degree of differentiation (rock from early to late DI and Rb/Sr were increased,DI =88.9 ～ 95.36,Rb/Sr =1.76 ～ 12.19),enriched in Rb,Th,U,Ta,Zr,Hf and HREE element,depleted in Ba,Sr,P,Ti and other elements,significant negative Eu anomalies (δEu =0.54 ～ 0.62,0.26 ～0.47,0.20 ～ 0.60).The P2O5 has the negative correlation with SiO2 while the Y has the positive correlation with the Rb.In summary,JCG shows characteristics of highly fractional I-type granite.Rock formation temperature decreased from early to late (average from 786℃ to 755℃).εHf(t) values of the majority is between 0.1 ～4.8,except a small number of ＜ 0,with the corresponding tDM2 range from 0.95 to 1.25Ga.Comprehensive inferred that the JCG result from extensive fractionation of hybrid magma,which combined the Proterozoic crust derived melts and lithospheric mantle derived melts.
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