东昆仑造山带多期隆升历史的地质热年代学证据

摘要

Multiple phases of Mesozoic and Cenozoic cooling and uplifting events are derived from fission track (FT) dating of zircons and apatites and thermal history modeling of apatite FT ages from several plutons in East Kunlun near Golmud City. Two phases of Mesozoic cooling histories revealed by zircon FT ages are phase I in Jurassic (194.1 -144.4 Ma) and phase II in Early Cretaceous (115.7~100.2 Ma). Three phases of Cenozoic cooling histories revealed by apatite FT ages and thermal history modeling are phase I in early Eocene (~52.9 Ma), phase II in middle Miocene (16.3~10.0 Ma), and phase III in Pliocene (5.1~0.9 Ma), which are considered to be closely related to the activity of Cenozoic East Kunlun thrust system. Cenozoic phase I (~52.9 Ma) cooling is consistent with the short time living of a small foreland basin formed on the north margin of the East Kunlun Mountains. The spatial distribution of apatiteFT ages in Cenozoic phase II (16.3-10.0 Ma) and III (5.1～0.9 Ma) suggests the piggyback thrusting of the East Kunlun thrust system and the forming of piggyback Qaidam Basin as a result of basin-mountain coupling. According to the age comparability of the end of thrusting in Cenozoic phase II and the beginning of the major sinistral strike-slipping of Kunlun Fault, it is inferred that there was a deformational transfer from compressing to shearing at ～10.0 Ma.%对格尔木附近东昆仑山花岗岩类侵入岩体中锆石和磷灰石进行裂变径迹(FT)定年与热历史的模拟,得到了中、新生代东昆仑山多阶段冷却与隆升的构造热历史.锆石FT年龄反映了东昆仑山中生代2期冷却历史,分别为第1期侏罗纪(194.1～144.4Ma)和第2期早白垩世(115.7～100.2Ma)冷却历史.磷灰石FT年龄和热历史模拟给出新生代3期冷却历史,分别为第1期始新世早期(约52.9Ma)、第2期中新世中期(16.3～10.0Ma)和第3期上新世(5.1～0.9Ma)冷却历史.东昆仑山新生代3期冷却历史与逆冲断层系的发育紧密相关.新生代第1期(约52.9Ma)可能反映了柴达木盆地南缘一个夭折了的前陆盆地的存在.新生代第2期(16.3～10.0Ma)和第3期(5.1～0.9Ma)冷却年龄具有规律性的空间分布,反映了东昆仑山背驮式逆冲断层系的发育历史,表明柴达木盆地主要是作为东昆仑山的背驮式盆地而建立盆山耦合关系的.根据新生代第2期冷却历史的结束与昆仑断裂大规模左行走滑运动开始的年龄对比,推测东昆仑山区域变形作用由挤压向剪切转换的时间可能在10.0Ma左右.