Longmenshan Nappe Structure
This nappe structure is located on the northwestern margin of the Sichuan Basin and has a NE trend. It starts in the southeast near Luding and extends northeast through Guanxian County, Wenchuan, and Mian County in Yangping, where it enters the Qinling Mountains. Its total length is approximately 600 km, and it forms an important geological demarcation line between eastern and western China. It is also associated with an obvious gravity gradient. The tectonic movements have been strong since the Mesozoic, resulting in an overthrust-nappe belt more than 30 km wide that forms the eastern border of the Qinghai-Tibet Plateau.