川西坳陷构造格局及其成因机制

Structural configuration and its genetic mechanism of the West Sichuan depression in China

川西坳陷是晚三叠世以来于四川盆地西部发育起来的前陆坳陷,经历了印支、燕山和喜马拉雅多期次构造运动。受西缘龙门山冲断带、北缘米仓山构造带和南缘川滇构造带的影响,川西坳陷相应发育北东向、近东西向和近南北向三组主要构造。川西坳陷现今构造具有东西倾向分带、南北走向分段和垂向分层的变形特点,据地表构造形迹和地腹构造展布,可划分为三个变形区(带):龙门山前缘扩展变形带主要受龙门山冲断带影响,发育北东向构造;川西北低平褶皱区同时受龙门山和米仓山构造带的影响,发育北东向和近东西向构造;川西南低缓断褶区同时受龙门山和川滇构造带的影响,发育北东向和近南北向构造。川西坳陷的构造形成受控于三大因素:基底结构和中下三叠统富膏盐岩层的分布提供了边界条件和物质基础,而周缘构造带影响下的多期、多组构造最终造就了倾向分带、走向分段、垂向分层以及复合-联合构造格局。

The West Sichuan depression is a foredeep developing in western Sichuan Basin since Late Triassic and has experienced multi-stage tectonic movements in Indosinian,Yanshanian and Himalayan.Affected by the Mt.Longmenshan thrust belt on the west side,Mt.Micangshan belt on the north side and Chuandian structural belt on the south side the NE-trending,sub-EW-trending and sub-NS-trending structures developed correspondingly in the West Sichuan depression.The present structural configuration is characterized by structural zonation in the dip direction,structural segmentation along the strike and structural delamination vertically.In term of the surface structural features and subsurface structural distribution,the West Sichuan depression can be divided into three deformation areas：（1） the expanded deformation belt along the front of Mt.Longmenshan,dominated by the NE-trending structures and affected only by the Mt.Longmenshan thrust belt;（2） the low-flat fold area in Northwest Sichuan,symbolized by the NE-and EW-trending structures related to Mt.Longmenshan and Mt.Micangshan belts;（3） the low-gentle fault-fold area in Southwest Sichuan,represented by the NE-and NS-trending structures associated with Mt.Longmenshan and Chuandian structural belts.The structure formation in the West Sichuan depression was controlled by three major factors as follows,the basement texture and gypsum-salt layers in Lower-Middle Triassic provided boundary conditions and material base,the multi-stage and multi-direction structures driven by peripheral structural belts coined eventually the structural framework of zonation,segmentation,delamination and compounding-combination superimposition.