阿尔金断裂晚新生代左旋走滑位错的地质新证据

摘要

Based on field observations,this paper analyses sedimentaryprocesses and deformation history of the strike-slip basins developed along the central segment of the Altyn Tagh Fault zone(located between long.88°E and long.92°E) and puts forwards to geological evidences for Late Cenozoic left-lateral strike-slip offset along the fault zone.This study shows that the Neogene strike-slip basins experienced an early pull-apart opening probably occurred during latest Miocene to Early Pliocene and a late extinction by left-lateral strike-slip faulting since Late Pliocene.Spatial distribution of Neogene sediments along two sides of the fault indicates a minimum left-lateral offset of 80 km.The vast Suoerkuli Basin developed in the Altyn Tagh Mountain was initially originated from an erosional basin during Neogene,which became the main source area for the deposition of the Qaidam Basin.This erosional basin was closed and evolved into a depositional basin during middle-Late Pleistocene.The outlet channels of the Neogene Suoerkuli basin have been displaced left-laterally for about 100 km by the active trace of the Altyn Tagh Fault.The mean rate of left-lateral slip on the Altyn Tagh Fault is estimated based on above observations taking into account the offsets of fluvial fan systems of the first-order rivers across the Altyn Tagh Mountain.%通过对沿阿尔金断裂中段(位于东经88°至92°)发育的晚第三纪走滑盆地沉积历史和走滑变形过程的野外观测以及对第四纪索尔库里盆地形成和演化过程的沉积环境复原的分析，提出了阿尔金断裂中段晚新生代左旋走滑位错的地质新证据。研究表明，晚第三纪走滑盆地经历了中新世晚期至上新世早期斜张走滑拉分和上新世晚期以来左旋错动的演化过程，沉积体沿断裂的错位分布特征指示至少发生了80km的左旋走滑位错。发育于阿尔金山链内部的索尔库里盆地起源于晚第三纪早期强烈的侵蚀作用，成为柴达木盆地快速沉积的主要物源区。该侵蚀盆地于中晚更新世闭合并演化成一个独立的沉积盆地。通过侵蚀盆地外流通道的复原指示阿尔金断裂自晚第三纪以来累积了80～100km的左旋位错。在此基础上，结合穿越断裂构造的Ⅰ级区域水系形成的洪积裙宽度和主干河道沿断裂迹线的拐折长度，探讨了阿尔金断裂晚新生代左旋走滑位错量沿走向分布的特征，估算了左旋走滑速率。