阿尔金断裂东端的旋转构造及其动力学意义

Tectonic Transformation in the Eastern Part of the Altun Fault

在阿尔金主断裂与祁连山北缘断裂的交汇部位 ,发育一个反时针旋转构造———照壁山旋转构造 ,它是新构造运动期阿尔金断裂左行走滑运动的结果。结合前人资料 ,对照壁山旋转构造变形及其发育过程进行了初步分析 ,认为阿尔金断裂与祁连山北缘断裂的构造转换是通过旋转构造变形来实现的。沿阿尔金断裂一系列旋转构造的存在和青藏高原东北缘旋转构造的发育表明 ,伴随青藏高原北部物质绕喜马拉雅东构造结的顺时针旋转运动 ,使旋转构造成为高原北部边缘带转换、吸收构造变形的重要表现形式。

The kinematic manner and transform relation between the Altun strike-slip fault zone and the northern thrust zone of the Qilian Mountains is the most important problem of intraplate deformation in the northern margin of the Qinghai-Tibet plateau, and is also one of the primary problems about the uplift of the Qinghai-Tibet plateau. How has the large strike-slip displacement of the Altun fault in the eastern part been absorbed by the northern Qilian Mountains fault zone? And what was the specific scheme of strain distribution in the region? Interpretation of remote sensing image and high-resolution aeroborne image of the region, together with field geological survey, combined with previous research results, it shows as follows: the neotectonic deformation at the cross point of the Altun fault and the northern Qilian thrust is absorbed, adjusted and transformed by rotational shear structural system. Some problems including development of Zhaobishan vortex structure at the eastern part of the Altun fault, activity of strike-slip of the Altun fault, forming age, deformation manner and progressive deforming process of the vortex structure are analyzed. We concluded that the Zhaobishan vortex structure was formed by the rotation of rock blocks surrounded by two groups of shear faults caused by intensive activity of strike-slip of the Altun fault in Cenozoic Era.The Zhaobishan Mountain serve as the axes of rotation, and Jiuxi depression, Changma depression, Daba depression together with the Altun Mountains, western part of north Qilian Mountains and Hongliuxia uplift acted as rotational shear zone of the vortex structure. During Quaternary period, destroying of the vortex structure, incision of its axes, and the deformation of eastern part of the Altun fault along one group of broom-shaped shear plane, represent the results of rotational shear movement at that stage. Based on decomposition of about 4mm/a strike-slip rate of eastern part of the Altun fault during late Quaternary, we obtained estimated rate of slipping along the Zhaobishan broom-shaped fault and the main north Qilian thrust. A group of arcuate faults represented by the Changma fault in the south part showing intensive activity in the late Quaternary, function as main passages of distribution of strain energy of strike-slip of eastern part of the Altun fault within Qilian Mountains. Except of the rotational shear structure at eastern part of the Altun fault, there are several other vortex structures existing in the southern part of the Altun fault and in the northeast margin of the Qinghai-Tibet plateau. Their existence show the importance of vortex structures being main manner of transformation and absorption of tectonic deformation in the north margin of the Qinghai-Tibet plateau, and reflecting clockwise rotation movement of the Qinghai-Tibet plateau centered with east Himalayas structural knots.