Cenozoic out-of-sequence thrusting and its control on drainage evolution in the eastern Tibetan Plateau

The Yalong-Yulong fault system (YYFS) is the principal thrust system along the eastern margin of the Tibetan Plateau and has been widely linked to the early topographic growth of the plateau margin. However, its growth history and its relationship to basin development and drainage evolution remain poorly constrained. Here, we integrate geochronological, thermochronological, and provenance data from the Yongning and Ninglang basins, located in the hanging walls of the Lijiang-Xiaojinhe and Jinhe-Qinghe faults (two major branches of the YYFS), respectively, to reconstruct the coupled evolution of major thrust faults, basin development, and regional drainage networks. Our results show that deposition in the Yongning Basin occurred between ∼36 and ∼20 Ma, postdating sedimentation in the more easterly Ninglang Basin, which ceased before ∼36 Ma. We interpret this diachronous basin development as reflecting diachronous fault growth, with deformation initiating along the eastern Jinhe-Qinghe Fault and subsequently shifting hinterlandward to the western Lijiang-Xiaojinhe Fault. The younger initiation of the hinterland Lijiang-Xiaojinhe Fault indicates that the YYFS evolved through out-of-sequence thrusting rather than simple forward propagation. Provenance data suggest the presence of an exorheic drainage system originating in the northwest and passing through the Yongning Basin during the late Eocene–Oligocene. More importantly, contrasting provenance signatures between the Yongning and Ninglang basins record a major reorganization of sediment-routing systems, which we interpret as a progressive westward deflection of the major exorheic drainage network driven by the out-of-sequence growth of the YYFS. These results provide basin-based constraints on the growth history of the YYFS and demonstrate that the geometry and kinematic evolution of major thrust faults exerted a first-order control on the development and reorganization of regional drainage networks in eastern Tibet.