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Understanding the geodynamics of plateau evolution necessitates careful consideration of the spatial and temporal constraints associated with mountain building on the northeastern Tibetan Plateau. However, when and how the northeastern Tibetan Plateau grew remains highly debatable. Here we integrate apatite U-Pb, fission-track, and rare-earth element provenance indicators from the Oligocene-Miocene continental succession of the Xunhua Basin to establish a framework of drainage reorganization and topographic evolution of the Xunhua region. The results suggest three provenance changes at ca. 28 Ma, ca. 20 Ma, and ca. 12 Ma, that not only indicate topographic growth of the West Qinling, Laji Shan, and Jishi Shan, respectively, but emphasize the significance of apatite for provenance analysis. The compilation of our findings and deformations within the northeastern Tibetan Plateau reveals the Oligocene-Miocene stepwise expansion and the Middle Miocene stress reorganization within the northeastern Tibetan Plateau. Combined with regional evidences, we propose that the Early Cenozoic northward compression of the Indian continent shortened and thickened Tibetan lithosphere, and subsequently triggered the removal of thickened lithosphere beneath south-central Tibet in the Oligocene. This process not only induced Oligocene-Miocene progressive expansion across the northeastern Tibetan Plateau, but also facilitated the continuous northward injection of the Indian lithosphere. Simultaneously, accompanied by the southward insertion of the North China craton, the underthrusting of both the India and North China initiated sinistral strike-slip faults in the middle Miocene, driving a change in stress directions. The results of this study underline the contribution of both the lithospheric removal and continental underthrusting geodynamic processes in driving outward growth of plateau.
Guo et al. (Fri,) studied this question.