Abstract:

According to the coupling relationship between basins and mountains and the depositional characteristics of the Xujiahe Formation in the western margin of Sichuan basin,it is deduced that Indosinian deformation occurred in three episodes in Longmengshan,with episodic progressive overthrust nappes developed from north to south.The early Indosinian episode happened during the deposition of the second member of Xujiahe Formation when the deformation was confined to the north section of Longmengshan;the middle Indosinian episode was within the deposition of the fourth member of Xujiahe Formation when the deformation was limited on the north part of the middle section of the mountain;and the late Indosinian episode was at the end of deposition of the Xujiahe Formation when the deformation was the strongest and most extensive in the study area.It is also noted that the Rhaetian deposits are generally absent in the western Sichuan basin with deformation of various degrees.

Key words: Indosinian episode, progressive deformation, chronogenesis, Longmenshan structural leelt