新疆东天山红云滩地区构造-热演化探讨：来自Ar-Ar和(U-Th)/He热年代学的约束

Thermo-tectonic evolution history of Hongyuntan area,eastern Tianshan,Xinjiang: Constrained from Ar-Ar and(U-Th)/He dating

红云滩岩体位于东天山觉罗塔格西部,对其进行热演化历史研究对于揭示觉罗塔格地区乃至整个东天山地区的构造-热演化历史具有重要意义。本文对红云滩岩体进行黑云母Ar-Ar、锆石（U-Th）/He和磷灰石（U-Th）/He测年,并结合前人的锆石U-Pb测年结果,精细刻画出该岩体自形成以后经历的热演化过程,并据此识别出东天山红云滩地区发生过多期快速抬升冷却事件。黑云母阶段升温Ar-Ar法同位素定年得到的坪年龄为316.9±1.8Ma,单颗粒锆石和磷灰石（U-Th）/He同位素定年得到的平均年龄分别为213.7±9.6Ma和65.5±1.3Ma。热年代学数据及模拟结果表明东天山红云滩地区自晚古生代以来经历了3个快速冷却阶段,分别为：晚石炭世至早二叠世（ca.330~296Ma）、晚三叠世（222~220Ma）、晚白垩世（91~77Ma）。其中,晚石炭世至早二叠世的快速冷却作用是岩体侵位后与围岩热传导冷却及伴随天山造山隆升冷却综合作用的结果,晚三叠世和晚白垩世的两期快速冷却事件分别与羌塘-欧亚板块、Kohistan-Dras岛弧-拉萨地块碰撞的远程效应造成的东天山地区隆升作用有关。新生代以来,红云滩岩体所在的阿奇山-雅满苏地区构造活动相对较弱,未发生较为明显的隆升作用,与天山西段新生代的构造活动有着明显的差异。

Hongyuntan rock mass is located in the West Jueluotage area,eastern Tianshan Mountain,Xingjiang,NW China.Research on the thermal evolution history of this rock mass can provide important evidence for constraining the thermal history of the whole eastern Tianshan Mountain. This study reports new biotite Ar / Ar age,zircon and apatite（ U-Th） / He ages of a same granodiorite sample from Hongyuntan rock mass,which,in conjunction with pre-existing zircon U-Pb age and inverse modeling simulations,constrain the thermal-tectonic history of Hongyuntan area. Biotite Ar-Ar dating yields a plateau age of 316. 9 ± 1. 8Ma. Zircon and apatite（ U-Th） / He dating yield weighted mean ages of 213. 7 ± 9. 6Ma and 65. 5 ± 1. 3Ma,respectively. Three fast cooling stages can be deduced by thermochronology data and inverse model simulation： Late Carboniferous epoch-Early Permian epoch（ ca. 330 ~296Ma）,Late Triassic epoch（ 222 ~ 220Ma） and Late Cretaceous epoch（ 91 ~ 77Ma）. It is indicated that the first fast cooling stage was caused by conductive cooling after emplacement and uplift cooling company with Tianshan orogeny. Late Triassic and Late Cretaceous epoch fast cooling were related to the uplift of eastern Tianshan,which were caused by far-field effects of Qiangtang-Eurasia collision and Kohistan-Dras-Lhasa collision,respectively. Low-temperature thermochronology results indicate that Aqishan-Yamansu area,where Hongyuntan rock mass located in,was stable during Cenozoic. This is a significant different with the Cenozoic tectonic evolution of the western Tianshan.