东昆仑山南缘大型转换挤压构造带和斜向俯冲作用

东昆仑地体和巴颜喀拉－－松潘甘孜地体之间的会聚边界是一条位于东昆仑南缘的大型转换挤压构造带。研究表明该带的东段（阿尼玛卿段）和西段（东－西大滩段）构造特征不同,阿尼玛卿段的构造以印支期具往南西造山极性的逆冲叠覆岩片和新生代脆性左行走滑构造为特征,东－西大滩段是由220Ma形成的EW向韧性左行走滑剪切带及两则伴生的挤压褶皱断裂带组成,韧性变形持续至20Ma,之后表现为脆性左行走滑构造再活动。因此,东昆仑南缘大型会聚带是一条由东段的“收缩挤压”为主向西段的“转换挤压”逐渐过度的特殊复杂的构造带,它的形成与巴颜喀拉－－松潘甘孜地体往NE方向斜向俯冲于东昆仑地体之下有关。

A Large Transpression Zone at the South Margin of the East Kunlun Mountains and Oblique Subduction

The convergence boundary between the East Kunlun terrane and the Bayan Har-Songpan Garze terrane of the Northern Tibet plateau is a large transpressional zone at the south margin of the East Kunlun Mountains. The deformation structures are different between the eastern segment (A' nyemaqen segment) and the western segment (eastern Datan and western Datan segment). The structures of the A'nyemaqen segment are characterized by superimposed thrust slices with southward erogenic polarity formed during the stage of Indosinian collision-orogeny and brittle sinistral strike-slip faults formed during Cenozoic. The eastern Datan and western Datan segment consists dominantly of an E-W-trending ductile sinistral strike-slip transpression zone com-panied by a NW-SE-trending fold and fault zone at its both sides, which formed 220 Ma ago. The ductile deformation continued till 220 Ma B. P. and then the deformation was manifested by the reactivation of the brittle sinistral strike-slip deformation structures. Therefore, the large convergence zone at the south margin of the East Kunlun Mountains is a very special tectonic zone which changed gradually from the " constrictive compression" in the eastern segment to the "transpression" in the western segment. Its formation was related to the northeastward oblique subduction of the Bayan Har-Songpan Garze terrane beneath the East Kunlun terrane since the Indosinian.