龙门山中段川西前陆盆地初始盆山边界及其变迁

The preliminary boundary of the West Sichuan foreland basin and orogenic belt and its migration in the central Longmen Mountains,Sichuan,China

通过对龙门山中段造山带、前陆盆地、飞来峰的构造变形和构造演化研究,结合前陆盆地物源分析,确定了盆山转换时期川西前陆盆地初始盆山边界,重塑了盆山边界的变迁过程。研究表明,盆山转换初期川西前陆盆地盆山初始边界断裂为茂汶断裂,现今分布于冲断带内的飞来峰均来自于茂县-汶川断裂与北川-映秀断裂之间的区域。印支-燕山期造山带向南东挤出,使位于茂县-汶川断裂带与映秀-北川断裂带间的地层发生变形和冲断隆升,形成北东向构造。作为前陆盆地基底的海相碳酸盐岩地层逐渐被抬升剥露,成为飞来峰的源。随着造山带不断地冲断隆升,前陆冲断带向南东扩展,盆山边界由初始的茂县-汶川断裂依次向南东迁移至北川-映秀断裂、彭-灌断裂和关口-彰明断裂以东。

Through comprehensive studies of the tectonic deformation and development of the orogenic belt,foreland basin,klippe and combined with the provenance analysis of the foreland basin,the preliminary boundary is determined and the migration process of the West Sichuan foreland basin is reconstructed.The research indicates that the preliminary boundary fault between the West Sichuan foreland basin and the orogenic belt is Maowen fault,and the klippes distributed over the thrust zone in the foreland basin were from the areas between the Maowen fault and the Beichuan-Yingxiu fault.The southeastern extrusion of the Songpan-Ganzi orogenic belt during the Indosinian-Yanshan epoch is responsible for the deformation and thrusting uplift of strata between the Maowen fault and the Beichuan-Yingxiu fault.It resulted in the development of NE trending structure.The exhumation of carbonate rock strata as the foreland basin basement is the potential roots of klippes.With the thrust sheets uplift and progression from NW to SE,the west boundary of the West Sichuan foreland basin migrates gradually from the preliminary Maoxian-Wenchuan fault to the Beichuan-Yingxiu fault,the Peng-Guan fault and the east of the Guankou-Zhangming fault in turn.