Lancang Fault Assists Block Extrusion in Southeastern Tibet During Early‐Middle Miocene

Abstract The tectonic and topographic evolution of the southeastern Tibetan Plateau based on low‐temperature thermochronology data is controversial, especially whether it is tectonically‐ or climatically‐controlled, especially along the Lancang fault (LCF) that links the flat central plateau to the west with the high relief southeastern Tibetan Plateau to the east. To explore the tectonic evolution of the LCF and its role in the tectonic and topographic evolution of the southeastern Tibetan Plateau, we carried out detailed field investigation and low‐temperature thermochronology (AHe, AFT, and ZHe) analyses. Field evidence indicate that the northern LCF splits into two branches, the Yangda‐Yaxu and Baqing‐Leiwuqi faults, the latter striking N50°W and dipping to the SW at ∼55°, exposing >100 m‐wide fault rocks composed of a fault damage zone, breccia, and gouge. New thermochronology data and thermo‐kinematic modeling results suggest rapid exhumation of the region located between these two fault branches during ∼22–10 Ma at an exhumation rate of ∼1.57 km/Ma, compared to slow cooling prior to 22 Ma and since 10 Ma. We propose that internal anti‐clockwise block rotation triggered rapid local exhumation, and that the final merging of different parts of the LCF during the Early‐Middle Miocene assisted the southeastward escape of Sundaland, which profoundly affected the evolution of the regional geomorphology.