晚三叠世-早侏罗世祁连山东部隆升的裂变径迹年代学证据及地质意义

祁连山东北部为青藏高原隆升和东扩的前锋带，新生代以来经历了快速隆升和强烈剥露改造过程，致使前新生代地层面目全非，中生代陆内构造演化事件研究仍较薄弱，缺乏年代学的约束.为揭示和分析祁连山东部中生代构造隆升时限与过程，进而探讨秦祁造山带中生代陆内构造演化特点及区域动力学环境.主要采用物源分析、碎屑沉积物及基岩磷灰石裂变径迹定年，并结合裂变径迹热史反演模拟技术开展研究.研究表明，研究区侏罗系龙凤山组为近源的断陷盆地沉积，物源主要来自其周邻前中生代地层；其碎屑磷灰石裂变径迹未发生重置，年龄、径迹长度特征表明其源区在晚三叠世（±215 Ma）出现了快速冷却事件，同时东北部基岩裂变径迹热史模拟结果亦显示其较好地记录了该期事件，这与前人利用40Ar-39Ar年代学所揭示的西秦岭地区中晚三叠世快速抬升事件具时空统一性.分析表明研究区晚三叠世-早侏罗世发生了快速抬升事件，并认为该构造隆升事件是对中晚三叠世勉略洋闭合、秦岭最终碰撞造山过程的响应. 

Late Triassic-Early Jurassic Uplifting in Eastern Qilian Mountain and Its Geological Significance: Evidence from Apatite Fission Track Thermochronology

The northeastern margin of the Qilian Mountain, which is the outer zone of the uplift and eastward expansion of Tibetan plateau, has undergone a rapid uplift and strong exhumation process since the Cenozoic. The Mesozoic tectonic evolution study remains very weak for without the chronological constraints because pre-Cenozoic strata in the area have been subjected to the later alteration. Based on the analysis of source of the clastic rocks, sedimentary characteristics and basement apatite fission track dating, this paper reveals the Mesozoic tectonic uplift timing and process of the eastern Qilian Mountains with inversion simulation of fission track thermal history, aims at further exploration of the Mesozoic intracontinental tectonic evolution and regional dynamic background in the Qin-Qi orogenic belt. The results show that the Longfengshan Formation is the rift basin sediment of near-source accumulation from the pre-Mesozoic strata. The detrital apatite fission track has not been annealed, and it still retains the history of uplift and erosion in its source area. The fission track age and the thermal history simulation show that the rapid cooling event occurred in Late Triassic (±215 Ma) in source area, which has also been recorded by thermal history simulation results of the northestern granite body. Our results show the same time-space characteristics with the rapid uplift of the West Qinling region previously revealed by 40Ar/39Ar chronology. Apatite fission track dating reveals a rapid uplift event of the study area in the Late Triassic-Early Jurassic. It is believed that the tectonic uplift event may have been a response to the closure of Mianlue Ocean and consequent collision orogeny in the Middle to Late Triassic.