柴达木盆地新生代演化及其构造重建——基于地震剖面的解释

CENOZOIC EVOLUTION AND TECTONIC RECONSTRUCTION OF THE QAIDAM BASIN: EVIDENCE FROM SEISMIC PROFILES

柴达木盆地是青藏高原内部最大的坳陷。柴达木盆地构造成因的研究，可以揭示青藏高原形成机制和生长历史。本文分析了柴达木盆地区域地震勘探剖面，得到如下认识：柴达木盆地一级构造为新生代宽缓复向斜，其振幅和半波长分别从柴西的〉16km和～170km变化为柴东的〈4km和～50km。褶皱首先在柴西贴近阿尔金断裂附近形成（65～50．5Ma），并向柴东扩展（23．3Ma）。复向斜的形成与较老的柴北缘逆冲断层系（65～50．5Ma）和较年轻的柴南缘逆冲断层系（35．5～23．3Ma）有关。盆地内部新生代上地壳缩短作用，由柴西的〉48％，向柴东减小到〈1％，说明在柴西和柴东之间，存在地壳加厚机制的渐进转换：柴西主要为上地壳缩短，柴东主要为下地壳缩短。

The Qaidam basin is the largest topographic depression inside the Tibetan plateau. Understanding the tectonic origin of the Qaidam basin has important implications for unraveling the formation mechanism and growth history of the Tibetan plateau. In this paper, the authors analyze regional seismic-reflection profiles across the basin. The first-order structure of the basin is a broad Cenozoic synelinorium, with an amplitude ranging from 〉 16 km in the west to 〈 4 km in the east. The fold axis propagated from the western Qaidam basin against the Ahyn Tagh fault at 65-50.5Ma to the eastern basin at 23.3Ma; its half-wavelength changes from ~ 170 km in the west to - 50 km in the east. The formation of the synelinorium was induced by an older thrust system initiated at -65-50.5Ma at the northern margin and a younger thrust system initiated at 35.5-23.3Ma at the southern margin. Cenozoic upper-crustal shortening decreases across the basin from 〉 48% in the west to 〈 1% in the east, suggesting a progressive shift in crustal thickening mechanisms across the Qaidam basin, from dominantly upper-crustal shortening in the west to dominantly lower-crustal shortening in the east.