阿尔金山新生代隆升历史:来自塔东南若羌凹陷的沉积记录

Cenozoic tectonic evolution of the Altyn Tagh:Evidence from sedimentary record in Ruoqiang depression of the southeastern Tarim Basin

阿尔金山位于青藏高原北部边缘,在高原隆升和演化过程中扮演着重要的角色。但是,关于它的新生代隆升历史现今仍存在较大的争议。阿尔金山北麓若羌凹陷新生代接受来自山脉的剥蚀物质。因此,凹陷内的沉积特征记录了阿尔金山新生代隆升的重要信息。本文利用石油钻井编录资料及地震剖面,通过对盆地区新生代各个地层之间的接触关系、沉积相组合和沉积速率变化进行研究,结果显示阿尔金山34Ma以来的隆升分为两阶段:第一阶段为34~20.4Ma,持续低速隆升;第二阶段为16Ma至现今,急剧快速隆升。结合前人研究成果,认为渐新世—早中新世,阿尔金断裂作为一个局限在中、下地壳的韧性剪切带造成阿尔金山一带产生大范围的地表隆起,控制了山脉在第一阶段的持续低速隆升;中中新世以来,阿尔金断裂大规模左行走滑,青藏高原北缘主要通过地壳缩短的形式释放应力,控制了山脉在第二阶段的急剧快速隆升。

Altyn Tagh defines the northern margin of the Tibetan Plateau,and plays an important role in understanding the rise and northward growth of the Tibetan Plateau.Its Cenozoic evolution remains controversial.The Ruoqiang depression in the SE Tarim Basin accumulated thick clastics sourced from the Altyn Tagh in the Cenozoic era,and thus bears important records concerning the Cenozoic uplift of the Altyn Tagh.In this paper,we studied the sedimentary facies and the sedimentary rates of the Cenozoic strata as well as their contact relationship in the Ruoqiang depression,based on newly obtained drilling data and high-resolution seismic reflection profiles.The result indicated that the Altyn Tagh was characterized by two-stage uplift since 34 Ma:Sustained weak uplift during 34~20.4 Ma and accelerated uplift since 16 Ma.We concluded that,together with previous studies,the sustained weak uplift of the Altyn Tagh in the first stage was caused by basal shear of the Altyn Tagh fault in the middle-lower crust;while the accelerated uplift in the second stage resulted from significantly lower strike-slip on the Altyn Tagh fault since the Mid-Miocene,which induced intense crustal shortening in the northern Tibetan Plateau.