阿尔金断裂新生代活动方式及其与柴达木盆地的耦合分析

Tectonic processes of the Cenozoic Altyn Tagh Fault and its coupling with the Qaidam Basin,NW China

位于青藏高原北缘的阿尔金左旋走滑断裂是世界上规模最大也是最重要的线性构造之一,其新生代以来的活动方式是限定高原生长机制的重要边界条件。本文在对阿尔金山中不同方向隆起构造进行分析的基础上,综合前人资料论证了阿尔金断裂在晚始新世-中中新世时以基底剪切为主,大规模地表走滑则发生在中中新世以后。对柴达木盆地内近东西向和北西向断裂系统的分布、形态、活动时间进行了详细的分析,发现它们是在不同时间、不同区域、不同控制条件下形成的两套断裂系统,与阿尔金断裂的两阶段活动方式存在很好的耦合关系。柴达木盆地西北侧的沉积和构造特征表明阿尔金山的隆升幅度和范围在中中新世达到最大,随后则逐渐减小,这种变化也与阿尔金断裂从基底剪切到地表走滑的转换非常吻合。

The active Altyn Tagh Fault in northern Tibetan Plateau is one of the largest and most significant linear structures in the world,and its Cenozoic activity is the important constraint on the growth mechanism of the Tibetan Plateau. In this paper,we illustrate that the Altyn Tagh Fault was dominated by basal shear during Late Eocene-Middle Miocene but by large-scale left-slip movement since then based on comprehensive analysis on uplifts of different trending in the Altyn Mountain and reported materials. We study systematically on the distribution,geometry and timing of the EW-and NW-trending fault systems inside the Qaidam Basin,and find that they are completely different fault systems forming in different time,different areas and controlled by different factors,showing a perfect coupling with the two-stage movement of the Cenozoic Altyn Tagh Fault. We also discover that height and width of the Altyn Mountain culminated in Mid-Miocene and then decreased according to the sedimentary and structural characteristics in NW Qaidam Basin,which can be well explained by the transition from basal shear to left-slip of the Altyn Tagh Fault.