新疆准噶尔晚古生代陆壳垂向生长(Ⅰ)——后碰撞深成岩浆活动的时限

Late Paleozoic vertical growth of continental crust around the Junggar Basin,Xinjiang,China(PartⅠ):Timing of post-collisionai plutonism

准噶尔是新疆北部古生代造山带的重要组成部分,以广泛发育晚古生代后碰撞花岗岩为特征,是中亚造山带中显生宙陆壳生长作用非常显著的地区之一。根据新近获得的SHRIMP锆石U-Pb年龄,并参考已经发表的锆石U-Pb年龄,本文重新厘定了准噶尔晚古生代后碰撞深成岩浆活动的时限。按照最新的国际地质年表中石炭纪和二叠纪划分方案(Gradstein et al．,2004),准噶尔后碰撞深成岩浆活动是从早石炭世中-晚维宪期开始、于早二叠世末期结束的。东准噶尔后碰撞深成岩浆活动发生在330～265Ma之间,而西准噶尔后碰撞深成岩浆活动的时限在340～275Ma之间,持续时间分别约65Ma。但是,在东准噶尔,后碰撞深成岩浆活动集中在330～310Ma和305～280Ma两个时段发生,而在西准噶尔,后碰撞深成岩浆活动的高峰发生在310～295Ma之间。准噶尔晚古生代后碰撞深成岩浆活动在空间上没有受到重要地质界线(如蛇绿岩带)的分隔控制,在有的地方花岗岩还可以侵位在蛇绿岩带之中。而晚古生代后碰撞深成岩浆活动不但在准噶尔分布广泛,而且在准噶尔北邻的阿尔泰造山带和南邻的天山造山带中均有出现,具有广泛的区域性。

As an important part of the Paleozoic orogenic belt in northern Xinjiang, the Junggar is characterized by intense and extensive development of Late Paleozoic granitoid plutons together with minor marie plutons, and it is one of the representative regions for the Phanerozoic continental crustal growth in the Central Asian Orogenic Belt. On the basis of new SHRIMP zircon U-Pb dating on the plutons in the East and West Junggar, in association with the zircon U-Pb ages from the literature, an attempt is made in this study to establish the timing of the late Paleozoic post-collisional plutonism in the region. It is concluded that the Late Paleozoic post- collisional plutonism occurred from middle-late Visean of Carboniferous to the end of Early Permian in accordance to the Geological Time Scale （Gradstein et al. , 2004）. Temporally, the plutons in the East and West Junggar formed in a period of 65Ma, from 330 to 265Ma and from 340 to 275Ma, respectively. However, the plutonism in the East Junggar showed two peaks of 330 to 310Ma and 305 to 280Ma, whereas most plutons in the West Junggar were emplaced from 310 to 295Ma. Spatially, the plutonism occurred in all tectonic units separated by ophiolite belts and even some granitoid plutons intruded in ophiolites. Furthermore, the post-collisional plutons can be found not only in the Junggar, but also in the Ahai orogenic belt to the north and in the Tianshan orogrnic belt to the south.