Structural controls on the jagged morphology of the Yangtze River: Conjugate faulting in the Lijiang-Dali area, southeastern Tibetan Plateau margin

The Jinsha River, the upper reach of the Yangtze River, displays a distinctly jagged planform along the southeastern margin of the Tibetan Plateau in the tectonically and seismically active Chuan-Dian Block. This study investigates the river’s morphology from a structural deformation perspective. Our mapping and structural analyses show that the river course corresponds more closely to the internal deformation framework of the Chuan-Dian Block than to the geometry of its major active boundary faults. The Lijiang-Dali region in the southern part of the block is cut by two groups of strike-slip faults—the Zhongdian and Lijiang fault systems trending NW-SE and NE-SW, respectively—which intersect to form an X-type conjugate fault system. New structural evidence indicates that these faults accommodate right-lateral and left-lateral movements, respectively, contrary to previous interpretations. We propose that this conjugate fault system reflects a regime of E-W contraction and N-S extension and has facilitated the development of a series of N-S−trending linear folds. The along-strike growth of these folds provides a plausible mechanism for the development of the Jinsha River’s characteristic bends. The conjugate faults appear to be part of a broader strike-slip network along the northeastern margin of the plateau and were active primarily at ca. 10 Ma; they jointly accommodate the eastward shortening and N-S extension of the Chuan-Dian Block in response to the northward movement of the Northeastern Syntaxis of the Himalayas. Although parts of the system have been locally overprinted by Quaternary extension—for example, where the Lijiang Fault is disrupted by the development of the Lijiang Basin—it remains active.