Southward propagation of the Karakoram fault system, southwest Tibet: Timing and magnitude of slip

The net slip on the southern portion of the Karakoram fault system in south west Tibet is estimated by restoring a piercing line defined by two key sur faces in the South Kailas thrust system, a regional counter thrust along th e Indus-Yalu suture, Assuming that the thrust system is planar across the K arakoram fault, we calculate 66 +/- 5.5 km of normal right slip. Documentat ion of the South Kailas thrust active at 13 Ma implies that the Karakoram f ault in southwest Tibet did not initiate until after the cessation of motio n on the thrust. However, field investigations of the central portion of th e Karakoram fault system document the fault to have been active at 17 Ma an d to have accumulated a maximum of 150 km of right slip. We suggest that th ese along-strike variations in the magnitude of slip and timing constraints are best explained by southward propagation of the Karakoram fault system. This is inconsistent with major right-lateral slip on the fault system, wh ich was used in support of extrusion models for Tibet.