小兴安岭东部早古生代花岗岩的发现及其构造意义

Discovery of Early Paleozoic granites in the eastern Xiao Hinggan Mountains, northeastern China and their tectonic significance

通过全岩-单矿物的Rb-Sr法和锆石激光剥蚀等离子体U-Pb法定年研究,确定小兴安岭东部地区存在508～471Ma的早古生代花岗岩。根据岩石学和年代学的特征,进一步将小兴安岭东部地区的早古生代花岗岩划分为与高级变质岩伴生的片麻状花岗闪长岩-二长花岗岩(508Ma±15Ma)、块状花岗闪长岩-二长花岗岩(499Ma±1Ma)和碱长-碱性花岗岩(471Ma±3Ma)3种岩石组合类型。上述3类花岗岩组合的依次出现反映了同碰撞-碰撞后伸展的构造演化特点,表明小兴安岭东部早古生代存在碰撞造山事件。

In this paper, the existence of 508-471 Ma Early Paleozoic granites is confirmed by using the whole rock-mineral separate Rb-Sr method and LA-ICP-MS zircon U-Pb dating method. Based on their petrology and geochronology, the Early Paleozoic granites may be subdivided into three rock associations, i.e.： gneissic granodiorite-monzogranite associated with high-grade metamorphic rocks （508±15 Ma）, massive granodiorite-monzogranite （499±1 Ma） and alkali-feldspar-alkaline granite （471±3Ma）. The successive occurrence of the three granite associations suggests that the tectonic evolution experienced syn-collisional to post-collisional extension, implying that a collisional orogenic event took place in the eastern Xiao Hinggan Mountains in the Early Paleozoic.