Cooling history of the Gongga batholith: Implications for the Xianshuihe Fault and Miocene kinematics of SE Tibet

Using thermochronological data and thermokinematic modeling, we constrain the timing of late Miocene exhumation of the northern portion of the Gongga batholith, located in Southeast Tibet along the Xianshuihe Fault (XF). We show that rapid exhumation started in the north of the Gongga batholith at ∼9 Ma at a rate of ∼1.85 km/Myr and slowed down since ∼4 Ma. A magmatic pulse occurring during the early Pliocene (∼4 Ma) has overprinted the rapid Miocene exhumation phase in some parts of the batholith, which record mainly early Pliocene post-magmatic cooling. Slow exhumation since ∼4 Ma is consistent with the present-day lower relief observed in the centre of the batholith, which contrasts with the rugged high peaks located to the south. We propose that the northern segment of the XF, the Yalahe fault, which is not active at present, was active between 9 and 4 Ma, forming a restraining bend that focused exhumation south of it. Since ∼4 Ma, the Selaha and the Zheduotang faults form the present-day restraining bend south of which the highest part of the massif is located, including the Gongga Shan that rises more than 3000 m above the mean elevation of the plateau. In the north of the batholith, similar peaks have been removed since the Miocene by local relief reduction at high elevations. Considering that the onset of motion along the XF is contemporaneous with the onset of rapid exhumation recorded along the Kangding transect at ∼9 Ma and a total offset of ∼62 km documented for the XF, the average slip rate of the XF is ∼7 mm/yr since 9 Ma.