presentationposted on 2020-07-14, 20:30 authored by Yiduo Liu, Xibin Tan, Yijian Ye, Chao Zhou, Renqi Lu, Michael A. Murphy, Xiwei Xu, John Suppe
Despite the common conception that erosion plays an important role in controlling along-strike variations in thrust-belt deformation, natural examples of focused erosion causing local variations of thrust-belt geometry, such as the formation of salients and recesses, remain underappreciated. Here we first build a classification diagram for recesses developing in critical-taper wedges, in which six independent variables lead to three morphotectonic scenarios regarding the effects of mass influx, mass efflux, and intrinsic properties of a thrust wedge. Then we investigate the structure, geomorphology, and erosion pattern along the Longmen Shan thrust system defining the eastern margin of the Tibetan Plateau. Our work shows a nearly constant surface slope across and an overall cylindrical fault-related fold geometry along the thrust belt. These phenomena can be explained by the development of a critically-tapered thrust wedge along the plateau margin. A prominent recess exists at the intersection between the transverse Minjiang River and the range-bounding thrust. There, the surface trace displays a much higher curvature than the rest of the thrust belt and the local fold geometry is conical rather than cylindrical. We infer a warped, decapitated passive-roof duplex under the recess. Formation of the Dujiangyan recess can be best attributed to localized fluvial erosion during forward propagation of the thrust wedge in eastern Tibet. This study sets a type example for map-view curves in thrust belts undergoing localized deformation-erosion interactions.