Analogue modeling of the northern Longmen Shan thrust belt (eastern margin of the Tibetan plateau) and strain analysis based on Particle Image Velocimetry

摘要

In response to the multistage convergences across the western margin of the Sichuan Basin, a complex thrust belt developed along the Longmen Shan thrust belt (LTB). Compressional analogue modeling with double weak detachments is carried out to shed light on the development and kinematics of the triangle zone at the front of the northern LTB. (1) Two weak detachments create an essential configuration for the development of duplexes. Each detachment displays different mechanical behaviors during the evolution of the thrust belt and decouples deformation at different depths. (2) Regular erosion at the thrust front can effectively localize strain and promote the development of the back-thrust along the upper detachment to generate a sustained passive-roof duplex in the front. The similarity of the tectonic deformation between the analogue modeling and northern LTB implies a possible evolutionary mechanism of the Shuangyushi Structure. The Middle Triassic and early Cambrian weak layers act as two pivotal detachments, decoupling the tectonic styles at different depths. During the Indosinian and Yanshanian period, continuous compression contributed to the establishment of the main tectonic framework of a passive-roof duplex. In the following Himalayan period, the eastward compression complicated the middle structural layer and uplifted the thrust front, and was accompanied by regular erosion, contributing to the development of a passive-roof duplex.