DYNAMIC INTERACTIONS BETWEEN HETEROGENEOUS EROSION AND CRUSTAL DEFORMATION IN A THREE-DIMENSIONAL THRUST WEDGE: THE DUJIANGYAN RECESS IN CENTRAL LONGMEN SHAN, EASTERN TIBET

Earth-surface processes can theoretically cause along-strike variation in structures of a thrust belt, as manifested by map-view curvatures (i.e., salient and recess). However, its natural example is rarely reported. We use the critical-taper wedge theory to categorize the formation mechanism of salient and recess by altering the six variables, one at a time, along the strike of a three-dimensional thrust wedge, namely, the shortening strain, wedge thickness, wedge strength, detachment strength, detachment dip, and erosion. We compare the conceptual models with the structure, topography, and erosion patterns of the Dujiangyan recess in the central Longmen Shan, eastern Tibetan Plateau margin. The Minjiang River transects the Dujiangyan recess and exerts localized fluvial shear stress on the bedrock. The surface slope and other variables show insignificant along-strike variations. We therefore conclude that the development of the Dujiangyan recess is modulated by the along-strike variation in erosion due to the presence of the Minjiang River. Moreover, the late Cenozoic deformation responsible for the salient-and-recess structure shows a similar strain pattern with the co-seismic vertical slip distribution of the 2008 Wenchuan Earthquake, indicating characteristic slip of the 2008 event.