Multi-level decollement zones and detachment deformation of Longmenshan thrust belt, Sichuan Basin, southwest China.

As is well known that many decollement layers were developed in the Longmenshan thrust belt, Sichuan Basin, China. Through field investigation, explanation of seismic profiles and analysis of the balanced sections, we can divide the decollement zones into 3 categories: (1) the deep level decollement zones, including the crust-mantle decollement layer, intracrustal decollement layer, and presinian basal decollement layer. The main structural styles of their deformation are the crust-mantle decoupling detachment deformation, the basal ductile shear deformation, etc.; (2) the middle level decollement zones, including the Cambrian-Ordovician decollement layer, the Silurian decollement layer, etc., the main structural styles of their deformation are the isopachous fold, the angular fold, the saddle structure, and the combination styles of them; and (3) the shallow level decollement zones, including the Xujiahe Formation decollement layer of Upper Triassic and the Jurassic decollement layers, the main structural styles of their deformation are the thrust-nappe tectonic, the pop-up, the triangle zone, the duplex, etc. Multi-level decollement zones not only made the Longmenshan thrust belt develop many different deformation styles from deep place to shallow place, but also made some local areas have the superimposition of the tectonic deformation apparently. This study indicates that the multi-level decollement zones have a very important effect on the shaping and evolution of the Longmenshan thrust belt. [ABSTRACT FROM AUTHOR]