秦昆结合区两期基性岩墙群^40Ar／^39Ar定年及其构造意义

秦昆(秦岭-昆仑)结合区在不同地质背景基础上于柴达木东缘次级造山带南东段的拉龙洼和满丈岗地区发育了两期基性岩墙群,~(40)Ar/~(39)Ar定年结果分别为393.5Ma和197.5Ma,它们分别代表着东古特提斯洋北支及其北侧秦昆间共和坳拉谷的初始伸展离散和这一构造系统封闭碰撞造山后的伸展垮塌构造岩浆事件。结合区域资料进一步分析表明,晚古生代中晚期东昆南-阿尼玛卿和阿尼玛卿-文县-勉略两支裂谷发育成相互沟通的东古特提斯洋北支时,苦海-赛什塘一支发生“夭折”而形成共和坳拉谷,这一构造系统于三叠纪晚期各区段几乎是同时发生收缩、闭合、碰撞造山,东昆南-阿尼玛卿-文县-勉略有限洋盆的向北俯冲碰撞造山形成统一的秦昆造山带,共和坳拉谷的封闭使西秦岭与东昆仑完成了侧向间的衔接。本文的研究给这一秦昆衔接的动力学演化过程提供了时代依据。

40Ar/39Ar Age of the Basic Sill Swarms of Two Periods in the Junction Area of Qinling and Kunlun and Its Tectonic Significance

Basic sill swarms of two periods were found in Lalongwa and Manzhanggang in the southeastern part of the secondary orogenic belt on the eastern margin of the Qaidam basin in the junction area of the Western Qinling and Eastern Kunlun orogenic belt. Their 40Ar/39Ar ages are 393. 5 Ma and 197. 5 Ma. The former was formed in the early period when the northern Paleo-Tethys and the Gonghe aulacogen between the western Qinling Mountains and eastern Kunlun Mountains began to be formed, whereas the latter marked extensional orogenic collapse after the tectonic system closed and collided to form an orogene. Comprehensive studies show that in the middle-late Paleozoic, when the rift from the southern Eastern Kunlun Mountains to A'nymaquen and the rift from A'nymaquen via Wenxian to Mianlue grew into an ocean, namely the northern branch of the Eastern Paleo-Tethys, the rift from Kuhai to Sertang between the Eastern Kunlun and Western Qinling Mountains failed and became the Gonghe Aulacogen. In the late Triassic, this tectonic system began to contract, close and collide to build mountains. Then the northern Eastern Paleo-Tethys was subducted under the Qaidam and Western Qinling terranes and collided to form the Qinling-Kunlun orogenic belt. The Western Qinling and Eastern Kunlun were finally joined laterally due to the closing of the Gonghe aulacogen. This research would provide evidence for the timing of the dynamic evolution of the Western Qinling and Eastern Kunlun Mountains and their junction.