Cenozoic crustal shortening and structural transition in the NW Yunnan basin region, SE Tibetan Plateau

Striking changes in kinematics and deformation styles often occur in convergent orogens in the later stages of their tectonic evolution, such as in the southeastern Tibetan Plateau, which transitioned from transpression to transtension and experienced kinematic reversal on regional fault systems since the Miocene, approximately 40 Ma after the initial collision. Although this shift has long been identified, the spatial patterns of onset and driving mechanisms are unclear, hindering an understanding of the processes and dynamics of intracontinental orogeny. We target the NW Yunnan basin region in the SE Tibetan Plateau. We conduct an integrative study of apatite (U-Th)/He and fission track thermochronology along with structural and sedimentary analysis to decipher the structural evolution of this region. Nearly E-W-directed shortening may have occurred during the Eocene to Oligocene, forming various-scale thrust and fold systems, widespread exhumation, and topographic uplift. Combined with existing data, this region has undergone a transition to transtension during the late Miocene-Pliocene, forming basin-and-range style landscapes. Furthermore, we explore the crustal deformation patterns and kinematics of major active faults based on newly processed geophysical data. Thickened crust in a hyper-oblique convergent zone would raise the temperature at depth and weaken the long-term strength of the upper mantle, especially in the presence of water. Such lithospheric conditions are more prone to localized tectonics and can cause late-stage orogenic gravitational collapse, driving striking structural transitions in the NW Yunnan basin region.