Deformation and Zonation of the Longmenshan Fold and Thrust Zone in the Western Sichuan Basin

Based on the geological surveying and seismic data,we divided the Longmenshan fold and thrust zone into five tectonic belts,that is,the Songpan-Graze tectonic belt to the west of the Qingchuan-Maowen fault,the ductility deformation tectonic belt between Qingchuan-Maowen fault and Beichuan-Yingxiu fault,the basement involution fold and thrust belt between Beichuan-Yingxiu fault and Majiaoba-Tongjichang-Shuangshi fault,the front fold and thrust belt between Majiaoba-Tongjichang-Shuangshi fault and Guangyuan-Guankou-Dayi fault,and the foreland depression belt to the east of Guangyuan-Guankou-Dayi fault.Each fault is tectonically characterized with piggyback propagation,with intense tectonic deformation in the Songpan-Graze tectonic belt and the ductility deformation tectonic belt where nappe structure were well developed.The tectonic deformation was weak in the front fold and thrust belt and the foreland depression belt where pop-up,fault related fold and so on were developed widely.While the northwestern area displays the features of a ductile deformation and gradually changes to ductile-brittle deformation and brittle deformation to the southeast.The depth of each fault decreased toward the basin from the seismic section.Zonation of Longmenshan fold and thrust belt was affected by many factors,the main factors of which are the tectonic setting,multiple decollement layers and lithology.