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The uplift and deformation styles of the Tibetan Plateau have been long debated on stepwise growth and crustal channel flow. Here, we offer new insight into this issue by constraining the pulsed exhumation history of the Yalong thrust belt in eastern Tibet, using apatite and zircon (U–Th)/He data from three ∼1 km vertical transects. The results revealed two rapid cooling pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35 °C/m.y.), respectively, which we ascribe to the staged‐thrusting faulting of this belt. These thrust faulting events indicated upward and eastward growth of the Tibetan Plateau, further suggested that the high topographic relief across the Yalong thrust belt mainly formed (at least) since the Late Oligocene. The available documents from paleoaltimetry, basin sediment accumulation, and thermochronometers and our new results reveal a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet. Plain Language Summary: The role of faulting in crust thickening has been one of the main controversies in the formation and evolution of the Tibetan Plateau. The Yalong thrust belt in eastern Tibet is a major Cenozoic structure with a 1.8–2.4 km topographic step, and its deformation processes are closely associated with the Cenozoic eastward plateau growth. In this study, we report 79 apatite and 78 zircon (U–Th)/He (AHe and ZHe) ages of 26 granitoid samples from three ∼1 km vertical transects. We suggest that the Yalong thrust belt underwent two rapid cooling (exhumation) pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35°C/m.y.), respectively. These pulses of exhumation and uplift along the Yalong thrust belt contributed to the development of the current morphology across eastern Tibet. Integrating previous findings and those reported in our study allow us to propose a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet. We suggest that the dynamic development of the deformation pattern may have been driven by the northward indentation of the Eastern Himalayan Syntaxis and the consequent lower crustal flow into southeastern Tibet. Key Points: The Yalong thrust belt underwent two rapid cooling pulses in the Late Oligocene (∼24 Ma) and Middle Miocene (17–14 Ma)The topographic relief across the Yalong thrust belt is mainly the result of pulsed thrusting at least since 24 MaA regional‐scale stepwise propagation pattern was proposed for the Middle–Late Cenozoic tectonic deformation in eastern Tibet [ABSTRACT FROM AUTHOR]

Abstract The uplift and deformation styles of the Tibetan Plateau have been long debated on stepwise growth and crustal channel flow. Here, we offer new insight into this issue by constraining the pulsed exhumation history of the Yalong thrust belt in eastern Tibet, using apatite and zircon (U–Th)/He data from three ∼1 km vertical transects. The results revealed two rapid cooling pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35 °C/m.y.), respectively, which we ascribe to the staged‐thrusting faulting of this belt. These thrust faulting events indicated upward and eastward growth of the Tibetan Plateau, further suggested that the high topographic relief across the Yalong thrust belt mainly formed (at least) since the Late Oligocene. The available documents from paleoaltimetry, basin sediment accumulation, and thermochronometers and our new results reveal a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet.

Thrusting implication in the crustal thickening history of eastern Tibet is highly debated. The ∼250 km‐long Muli thrust of the Yalong thrust belt in SE Tibet is a major Miocene structure with a pronounced topographic step (∼2,000 m). Using thermo‐kinematic modeling based on thermochronology data, we constrain the crustal geometry of the thrust as being steep (>70°) at the surface, in agreement with field observations, and flattening at depth (≥20 km) on an intra‐crustal décollement. Thrusting motion on the fault shows a velocity of 0.2 ± 0.06 km/Ma since 50 Ma, followed by an acceleration at a rate of 0.6 ± 0.08 km/Ma starting at 12.5 ± 1 Ma, yielding a total of ∼15 km of exhumed crust. Deeper, deformation may be localized through a ductile shear zone, and be related to the ∼15 km Moho step and shear wave velocity contrast imaged by tomography beneath the Yalong thrust belt. Plain Language Summary: The India‐Eurasia collision (∼50 million years ago [Ma]) led to the formation of the Tibetan Plateau, the world's largest and highest orogenic plateau. The formation and evolution of such a unique geological feature has been one of the main controversies in Earth Sciences for decades, especially regarding the role of faulting in the thickening of the crust. Here, we present 3D thermo‐kinematic models of thermochronology data allowing to constrain the exhumation history of the Muli thrust fault, a ∼250 km‐long major structure of the SE Tibetan margin, linked to significant steps in surface topography and in crustal boundary at depth (Moho). We constrain a steep fault (>70°) within the upper crust, consistent with field observations, that flattens at depth (≥20 km). The Muli thrust presents rapid thrusting motion (0.6 ± 0.08 km/Ma) that initiated at ∼12.5 Ma, following a slower phase (0.2 ± 0.06 km/Ma) since 50 Ma, with total rock exhumation of ∼15 km. This underlines the important role of thrust faulting in the thickening of the SE Tibetan crust. Key Points: Thermo‐kinematic modeling of Muli thrust, a major thrust fault of SE Tibetan Plateau15 km crust exhumation in 50 Ma on a high‐angle (>70°) ramp—décollement fault linked to thickening of SE Tibetan crustFault related to significant Moho step and shear wave velocity contrast in deep crust suggests entire crust implication [ABSTRACT FROM AUTHOR]

Rapid denudation and uplift of eastern Tibet have accelerated during the Late Miocene due to lateral lower crustal flow, without a significant contribution from upper crustal shortening. However, growing lines of evidence have revealed that Early Cenozoic faulting controlled enhanced denudation and shortening. Here, we report 51 new zircon and apatite (U Th)/He and apatite fission-track ages from seven granite samples along one primary branch fault (the Yunongxi fault) of the Yalong thrust belt in eastern Tibet. Cooling ages and inverse thermal modeling revealed two pulses of accelerated exhumation during the Late Cretaceous (70–65 Ma) and the Late Eocene–Early Oligocene (40–30 Ma). We suspect that the surface uplift of eastern Tibet, due to the convergence rate acceleration between India and Eurasia, triggered the first cooling stage. A synchronous out-of-pace Early Cenozoic cooling pattern across the Yunongxi fault was further identified and could be due to fault initiation at ca. 40–30 Ma. We argue that the Late Eocene–Early Oligocene rapid cooling and exhumation and the associated outward plateau growth were primarily accommodated through upper-crust faulting along the Yalong–Longmen Shan thrust belt. This deformation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet. More extensive Late Miocene deformation driven by lateral lower crustal flow consequently bypassed these early-stage fault systems and overwhelmed the Late Cretaceous and Late Eocene–Early Oligocene deformation in eastern Tibet. • The footwall of Yunongxi fault underwent accelerated exhumation during the Late Cretaceous and Late Eocene–Early Oligocene. • The striking differential cooling across the Yunongxi fault was most likely due to fault initiation ca. 40–30 Ma. • The second exhumation pulse was the first-stage response of fault activity to the India–Eurasia collision in eastern Tibet. [ABSTRACT FROM AUTHOR]