青藏高原东北缘龙首山晚新生代多阶段构造隆升的盆地记录

龙首山地区位于青藏高原与阿拉善地块的结合部位，其盆山演化过程和断裂带扩展模式的恢复对揭示青藏高原新生代北东向生长具有重要意义。本文基于龙首山南北两麓3个新近系沉积剖面的构造特征和5个砂岩样品的碎屑锆石U-Pb同位素LA-ICP-MS年龄结果，重建了青藏高原东北缘龙首山地区晚新生代的盆山演化过程。研究结果显示，龙首山地区晚新生代沉积-构造演化经历了3个主要阶段：（1）~14Ma，龙首山南缘断裂带活化，阿拉善地块南缘沿此断裂逆冲于张掖盆地之上，张掖盆地开始接收阿拉善地块的物源；（2）~5Ma，龙首山南缘断裂带的次级断裂开始发育，使龙首山南侧山麓白垩系开始剥露并为张掖盆地提供物源，同时，龙首山北缘断裂带活化并导致潮水盆地发生挠曲沉降，接收龙首山的物源；（3）5~2.5Ma，龙首山北缘断裂带的次级断裂开始发育，导致龙首山北麓白垩系开始剥露并为潮水盆地提供物源。通过对龙首山周缘盆地沉积相和物源开展分析，本研究反演了龙首山地区中新世以来的断裂带活动和山体隆升过程，表明在14~2.5Ma，随着龙首山南缘断裂、北缘断裂的活化和次级断裂的发育，龙首山经历了3次强烈的隆升，这对揭示青藏高原北东向的扩展过程具有重要的指示意义。

Basin response of muti-stage tectonic uplift of the Longshoushan area since the Late Cenozoic in northeastern margin of the Qinghai-Tibet Plateau

The Longshoushan region is located at the conjunction area of the Qinghai-Tibet Plateau and the Alxa Block, and the reconstruction of its basin-mountain evolution process and fault zone expansion model is of importance in understanding the northeastward growth of the Qinghai-Tibet Plateau since Late Cenozoic. Based on the structural characteristics of three Neogene sedimentary profiles on the northern and southern flanks of the Longshoushan and the zircon U-Pb ages of five sandstone samples from these profiles, the Late Cenozoic basin-mountain processes of the Longshoushan region were reconstructed. Three-stage evolution is suggested as follows: (1) At~14Ma, the South Longshoushan Fault was activated, resulting in the thrusting of the Alxa Block upon the Zhangye Basin, and the latter began to receive source materials from the former. (2) At~5Ma, with the expansion of the South Longshoushan Fault, the Cretaceous formations in the southern flank of the Longshoushan were exhumated and thus provided materials for the Zhangye Basin. Meanwhile, the Chaoshui Basin on the northern flank of the Longshoushan occurred flexural subsidence due to the activation of the North Longshoushan Fault, and thus received sediments from the Longshoushan as well. (3) During 5~2.5Ma, the continuous thrusting of the North Longshoushan Fault resulted in the uplift and denudation of the Cretaceous formations, and these strata became the sources for the Chaoshui Basin. The results from studies on sedimentary facies and provenance analysis of the Cenozoic strata indicate that the Longshoushan area had undergone a three-stage uplift during 14~2.5Ma associated with the thrusting and expansion of the North and South Longshoushan faults, as responding to the ongoing northeastward shortening of the plateau to accommodate the Eurasia-India continental collision.