新疆东天山哈尔里克山石炭纪花岗岩锆石U-Pb年龄、成因演化及地质意义

Zircon U-Pb ages, genetic evolution and geological significance of Carboniferous granites in the Harlik Mountain, East Tianshan, Xinjiang

新疆北部广泛发育的石炭纪—二叠纪花岗质岩石一直是中亚造山带西段研究的热点之一。新获得东天山哈尔里克地区小铺黑云母二长花岗岩和沁城南含角闪石二长花岗岩LA-ICP-MS锆石U-Pb年龄分别为316±4Ma和320±3Ma。地球化学特征显示,小铺岩体为弱过铝质高钾钙碱性I型花岗岩,沁城南岩体为准铝质高钾钙碱性A型花岗岩。小铺岩体的εHf(t)值为+8.0^+13.8,沁城南岩体则更高,达到+10.8^+16.7,对应的地壳模式年龄(TDMc)分别为822~450Ma和641~268Ma,反映源区为年轻地壳物质。结合区域同时代产出的基性岩,指示这些年轻物质很可能与新的幔源基性底侵岩浆有关,为北疆哈尔里克地区石炭纪后碰撞地壳垂向生长提供了新证据。此外,沁城南岩体具有A型特征花岗岩的出现,进一步揭示晚石炭世为碰撞-后碰撞的重要构造转换期。

Extensively developed granitoids in northern Xinjiang have constituted one of the hotspots in the study of granite in the western Central Asian Orogenic Belt. LA-ICP-MS zircon U-Pb analysis of the Xiaopu biotite monzogranite and Qinchengnan hornblende monzogranite in the Harlic area yielded crystallization ages of 316±4 Ma and 320±3 Ma. Their petrological and geochemical characteristics show that Xiaopu pluton belongs to high-K calc-alkaline and weakly peraluminous series of I-type granite, whereas the Qinchengnan pluton belongs to high-K calc-alkaline and metaluminous series with A-type granite characteristics. The Xiaopu pluton has positive zircon εHf（t） values of ＋8.0 ~ ＋13.8, and the Qinchengnan pluton has higher εHf（t） values up to＋10.8~＋16.7, with corresponding Hf model ages（TDMc） of 822~450 Ma and 641~268 Ma, respectively. These isotopic compositions indicate that young crust served as the main source of the granite generation. Combined with coeval basic rocks with similar isotopiccompositions in this region, it can be believed that these young granites might have been related to the new mantle-derived basic magma underplating and exhibited the post-collision vertical growth. Additionally, the Qinchengnan granites have A-type granite characteristics, thus providing a further evidence for the transition period of Late Carboniferous from collision to post-collision settings.