Late Miocene onset of the Litang–Batang conjugate strike-slip fault system: implications for southward expansion of the Chuandian Block, southeastern Tibet

The Batang and Litang faults constitute a conjugate strike-slip fault in the Chuandian Block, southeastern Tibet, but their role in accommodating deformation of the Tibetan Plateau remains unknown due to poor constraints on the deformation history of the Batang fault. Structural analysis indicates that the Batang fault is a right-lateral transtensive fault. Restoration of the deflected Jinsha and Lancang rivers yields cumulative right-lateral offsets of 10.5–29.1 km. Apatite fission track and apatite and zircon (U–Th)/He data, assisted by thermal modelling, reveal three-stage accelerated cooling at 19–16 Ma, at 7–5 Ma and since 2 Ma in the fault footwall. Notably, accelerated cooling at 7–5 Ma was interpreted as recording onset of the fault, consistent with geological cross-cutting relationships, yielding a geological slip rate of 3.6 ± 1.2 mm a −1 . The synchroneity of the transtensive Batang and Litang faults suggests that they formed a V-shaped conjugate strike-slip fault at slip rates <5 mm a −1 since 7–5 Ma, contrasting with fast-slip (5–10 mm a −1 ) faults bounding the Chuandian Block. These findings demonstrate that the conjugate strike-slip faults serve as a passive marker for the weakened lower crust beneath the block interior, while the fast-slip faults on the block margins have predominantly accommodated southward extrusion of the Tibetan Plateau.