Evolution of the Xiaojiang Fault in Response to India-Eurasia Collision: Evidence from Basin Filling Analysis and Low-Temperature Thermochronology

The evolution of the Xiaojiang fault (XJF), located on the southeastern margin of the Tibetan Plateau (SMTP), is closely tied to the ongoing deformations driven by the collision between India and Eurasia. Previous studies of the XJF have focused primarily on its late Miocene strike-slip activity, leaving unresolved whether the fault responded to earlier tectonic expansion of the SMTP during the Late Eocene–Early Miocene. In this study, we analyze basin filling patterns in the southern XJF and conduct low-temperature thermochronology on granite samples along this section. Our results identify an angle unconformity contact between the Yanshan Formation (E₂y) and the Xiaolongtan Formation (N₁x), accompanied by two distinct rapid cooling phases dated to 28-14 Ma and 13-5 Ma. Thermochronologic data further reveal that cooling propagated spatially outward from the XJF but remained restricted to a narrow zone, propagated spatially outward from the XJF but remained restricted to a narrow zone. We propose that rapid cooling from 28 to 14 Ma, coincided with thrust-dominated activity along the XJF, whereas regional uplift of the central Yunnan block only became apparent after late Miocene. Subsequent to the late Miocene, the XJF transitioned to dominantly strike-slip motion, synchronous with the activation of the Xianshuihe strike-slip fault and regional surface uplift across SMTP.