Whether tectonic strain from the early stage India‐Asia collision has synchronously affected the far‐field margin of the Tibetan Plateau is crucial for understanding plateau deformation and growth processes. However, direct evidence for early far‐field deformation remains scarce. Utilizing illite K‐Ar dating of three fault gouge samples, we established the faulting history of the Leibo fault zone (LFZ) at the southeastern margin of the Tibetan Plateau (SEMTP). Consistent authigenic illite ages of 52 ± 2, 54 ± 12 and 55 ± 6 Ma suggest the reactivated thrust faulting of the LFZ in the Early Cenozoic. Positioned ∼700 km east of the collisional boundary and at the intersection of three blocks with distinct lithospheric rheology in strength/viscosity, this event suggests a quasi‐synchronous far‐field tectonic response in the SEMTP to the India‐Asia collision.

The occurrence of a sharp turn along the upper course of the Yangtze River is referred to as the “Great Bend” and represents a large-scale drainage reorganization in response to the surface rise of the Tibetan Plateau. However, the timing and mechanism of the formation of the Great Bend remain disputed. In this paper, we report new (U–Th)/He and apatite fission track thermochronological data from the deep river valley in the Great Bend area of the southeastern margin of the Tibetan Plateau. Compared with the adjacent Jianchuan Basin, two phases of younger rapid cooling for the Great Bend area are identified based on thermal-history modeling, namely, Miocene (ca. 17 to 11–8 Ma) and Quaternary, with the former phase being contemporaneous with the formation of the anticline in the Tiger Leaping Gorge. Progressive increases in the normalized channel steepness (k_sn) and the degree of river-valley incision with increasing distance downstream for tributaries of the Yangtze River in the Tiger Leaping Gorge indicate that river rerouting and formation of the Great Bend occurred during the Miocene. Samples located at the bottom of the Tiger Leaping Gorge also reveal a phase of rapid cooling since ca. 1.9 Ma, with an exhumation rate of 1.5 ± 0.2 mm/year. We hypothesize that enhanced Quaternary exhumation in the southeastern margin of the Tibetan Plateau occurred mainly within the narrow region between the Sichuan Basin and the Eastern Himalayan Syntaxis, corresponding to an episode of widespread extensional deformation superimposed above middle- to upper-crustal flexure in this region.

The rearrangement of drainage basins provides critical insight into crustal deformation and geodynamic mechanisms. Near the southeastern boundary of the Tibetan Plateau, the Dadu River abruptly shifts from south- to east-flowing, providing important implications for regional tectonogeomorphic development since the mid-Pleistocene. South of the bend, the headwaters of the Anning River occupy an unusually wide valley. Field investigations show that large quantities of fluvial/lacustrine sediments are widespread along the Dadu and Anning rivers and are exposed at their drainage divide. Detrital zircon U-Pb age patterns confirm that these fluvial/lacustrine sediments are the remnants of the paleo-Dadu River, which strongly suggests that the paleo-Dadu River originally flowed southward into the Anning River. The cosmogenic nuclide burial ages of the lacustrine sediments along the Dadu and Anning rivers suggest deposition of these sediments from separate dammed lakes ca. 1.2 Ma ago, ca. 0.6 Ma ago, and ca. 0.9 Ma ago from north to south, respectively. Provenance and burial-age studies indicate that reorganization of the Dadu drainage occurred within the last 0.6 Ma. We propose that this drainage reorganization in southeastern Tibet resulted from progressive convergence between the India and Eurasian plates during the Pleistocene.

The Xianshuihe-Anninghe fault extents SE–S and constitutes the southeastern margin of the Tibetan Plateau. However, the associated Dadu River does not flow following the fault, but makes a 90º turn within a distance of 1 km at Shimian, heading east, and joins the Yangtze River, finally flowing into the East China Sea. Adjacent to the abrupt turn, a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault. Therefore, many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River. However, evidences for the capture of the integrated N–S paleo-Dadu-Anning River, its timing, and causes are still insufficient. This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers. Similar with sands in the modern Dadu River, the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz (>50%), anorthite (about 10%), orthoclase (about 5%), muscovite (about 5%), and clinochlore (about 4%). Correspondingly, bulk major elements show high SiO₂, with all samples >60%, and some of them >70%, low TiO₂ (≤0.75%), P₂O₅ (≤0.55%), FeO* (≤5%), and relatively high CaO (1.02%–8.51%), Na₂O (1.60%–2.52%), and K₂O (2.17%–2.71%), with a uniform REE patterns. Therefore, synthesizing all these results indicate that these lacustrine sediments have similar material sources, which are mainly derived from its course in the Songpan-Ganzi flysch block, implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake. The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the Xianshuihe-Xiaojiang fault system.

The youngest tectonic structures in Tibet are a series of grabens trending approximately north-south. However, the grabens in central Tibet are less prominent than those in southern Tibet, which suggests that there is spatial variability in deformation mechanisms. The Chem Co half-graben is situated in the westernmost segment of central Tibet and is characterized by boundary normal faulting that occurred during the late Quaternary. The bedrock exposure ages, as recorded by cosmogenic nuclides 10Be and 26Al, vary linearly with elevation along the normal fault plane, yielding an average extension rate of 2.2−2.4 mm/yr. This millennial extension rate is ten times higher than the long-term rate (i.e., 0.3−0.4 mm/yr over millions of years), suggesting an episode of accelerated extension. We performed lithospheric flexure modeling to simulate extension of the westernmost segment of central Tibet. The results reveal heterogeneous σ2 stress concentrations at depth, suggesting that the accelerated extension is most plausibly the result of localized stress concentrations associated with lateral variations in crustal rheology. By comparing the material loss calculated from the extensional rates and crustal thinning, it seems that the eastward spread of crustal material is decoupled from the middle–lower crust but is affected by its upwelling. Therefore, the direct effects of convergence between India and Eurasia are less prominent in central Tibet, except for its western part, where rapid uplift continues owing to oblique collision.