Tectonic Model and Genetic Mechanism of Kuangshanliang Anticline in Northwestern Margin of Sichuan Basin

Abstract:

Understanding the geological structure and tectonic evolution process of the piedmont thrust belt can provide reliable basis for studying the factors of basin-mountain transformation and the mechanism of intra-continental orogenic deformation. The Kuangshanliang anticline which located in the northern part of the Longmen mountain foreland thrust belt is an ideal place to study the process of intra-continental orogeny. In this paper, shallow surface geological structure and deep geological structure of Kuangshanliang anticline are depicted by drilling, field geological outcrop information and high-resolution three-dimension seismic data, and the multi-layer detachment model of Kuangshanliang anticline is established comprehensively. Through 2D MOVE software and tectonic sandbox modelling, the structure quantitative analysis and verification of the Kuangshanliang anticline are carried out in combination with inversion, providing a reliable scientific basis for studying the transition mechanism of the Longmenshan foreland thrust belt in the basin and mountain.

The results are as follows: The delamination deformation of the anticline of the Kuangshanliang is caused by the delamination of the Cambrian, Silurian and Triassic Feixianguan formation.The Kuangshanliang anticline can be divided into allochthone (Luziba-Shanliang anticline core thrust nappe), parautochthone (Deep Cambrian - Feixianguan formation duplex structure) and autochthone (Jialingjiang Formation - Cretaceous at the front limb of Kuangshanliang anticline).The formation and evolution of the Kuangshanliang anticline were controlled by the Late Triassic Indochina movement, the late Jurassic to Cretaceous Yanshan movement and the late Cenozoic Himalayan orogeny. The tectonic restoration results show that the total shortening amount is 42 km and the total shortening rate is 55.4%.Tectonic sandbox modelling indicates that the anticline of KuangShanliang is in the state of supercritical (critical taper angle is about 10°) before late Cenozoic, and the tectonic movement of the late Cenozoic leads to the development of the foreland thrust belt, making the angle less than the critical taper angle and returning to the steady state.