New insights into structural characteristics in central-northern Longmen Mountains: implications for multiple-decollement deformation

Abstract

The central-northern segment of the Longmen Mountains is located in the transfer zone, for which the structural characteristics are little studied. Based on the reprocessed two-dimensional seismic data, this work used methods such as field geological investigation, drilling analysis and structural interpretation to comprehensively study the structural characteristics in the central-northern segment of the Longmen Mountains. The thick belt is characterized by deep and ductile deformation and shows the combination styles of a series of tight anticlines and synclines. The transition belt I developed many imbricate faults which cut to the ground surface. The main faults in the transition belt I derived many secondary gently dipping faults in the footwall, which controlled the development of the relative fault-propagation folds. The transition belt Ⅱ is a buried structure that includes the No.1 fault. The intense imbricate thrust structures occurred in its hanging wall and the autochthonous structure with weak fold deformation developed in its footwall. This study provides new insight that the high-angle thrust faults commonly derive secondary gently dipping faults in the footwall, and both of them formed the falling-γ type of the structure style. According to the analysis of the structure characteristics and mechanism origin, it is suggested that the composite structure styles combining the imbricate and falling-γ type are the basic structure styles in the study area, which is controlled by the multiple-decollement deformation from the deep layer to the shallow layer as well as from the trailing edge to the leading edge.

Keywords

• structural characteristics
• structural style
• multiple-decollement deformation
• central-northern segment of longmen mountains