南祁连奥陶纪花岗岩锆石U-Pb年龄及地质意义

加里东运动是祁连山早古生代以来较为重要的构造变形期, 其中以发生在晚志留世与早泥盆世之间的构造活动最为强烈。在加里东早期开始有花岗岩类侵入体涌现, 到加里东晚期时, 南祁连出现较发育的中-酸性侵入岩, 并尤以南祁连西段较为集中, 这些岩体见于哈拉湖周围以及阳康、织合玛等地。应用激光烧蚀多接收器电感耦合等离子体质谱仪(LA-MC-ICPMS)方法, 对南祁连扫迪南部侵位于志留系巴龙贡葛尔组(Sb)中的花岗岩体进行了精确的锆石U-Pb定年研究, 结果表明, 花岗岩中锆石206Pb/238U年龄平均值为461.5±1.6 Ma, 指示扫迪南花岗岩体的地质时代属中奥陶世晚期, 故巴龙贡葛尔组(Sb)时代应该早于中奥陶世。 

ZIRCON U-Pb AGE FOR GRANITE OF THE ORDOVICIAN FORMATION AND ITS TECTONIC SIGNIFICANCE IN THE SOUTHERN QILIAN

Caledonian movement is a very important tectonic deformation stage since the Early Paleozoic in Qilian. The most intense tectonic activity began to emerge between the late Silurian and Early Devonian. The granitic intrusive began to emerge in early Caledonian movement. To the late Caledonian movement, South Qiian is developed in neutral-acidic intrusive rocks, and especially in the south western part of Qilian is relatively concentrated, the rock mass around in Hala Lake and Yangkang, Zhihema, etc. We made zircon U-Pb dating for granite by LA-MC-ICPMS. Zircon U-Pb age determination results show that, the formation of granite at the age of 461.5±1.6 Ma. It indicates that the geological age of granite in Saodi belongs to Middle Ordovician. Thus, the Balonggonggeer Formation should be earlier than the Middle Ordovician.