东昆仑造山带前陆盆地的叠加褶皱及其变形机制

SUPERIMPOSED FOLDS AND CORRESPONDING DEFORMATION MECHANISM IN FORELAND BASINS IN EASTERN KUNLUN OROGENIC ZONE

在东昆仑造山带的三叠纪洪水川群复理石岩系中，发育着两组斜歪－倒转褶皱：一组轴迹方向为北西向，与造山带主体构造线近一致；另一组为新发现的北东向，与造山带主体构造线近垂直，形成叠加褶皱．每一组褶皱均是压扁、纯剪切、纯剪切＋简单剪切三种变形机制的产物．北西向褶皱轴面的南西倒和北东向褶皱轴面的北西倒，与国内外典型的前陆盆地中的褶皱形态不尽相同，反映了动力基础是板块碰撞之后的近于垂直的北东及北西方向挤压应力相继作用下形成的叠加褶皱．北东向褶皱的发现，揭示了造山带中构造应力场的转换．

Two groups of oblique_overturned folds in the flysch rock series are located in Triassic Hongshuichuan Group, Eastern Kunlun orogenic zone, Northwestern China. The direction of the axial trace for one group of folds is a north_west one, nearly in agreement with the major structural lines in the orogenic zone. That for the other group is a newly_discovered north_east one, approximately perpendicular to the major structural lines in the orogenic zone. In this way, the two folds overlapped each other. Each group of folds is a product of three deformation mechanisms: flattening, pure shearing, and pure shearing + simple shearing. The south_west side of the north_west folding axial plane and the north_west side of the north_east folding axial plane are slightly different from those folding shapes in the typical foreland basins both inside and outside China, which indicates that they are dynamically superimposed folds that resulted from the two north_east and north_west compressive stresses approximately perpendicular to each other after the plate collision. The first discovery of the north_east folds reveals the transformation of the structural stress fields in the orogenic zone.