The neotectonic setting of conjugate strike-slip faults in central Tibet

The Indian subcontinent has penetrated more than 2500 km into the southern margin of Eurasia. However, an outstanding question remains. How is convergence related to the Indo-Asian collision partitioned throughout the orogen? Previous studies have focused on the boundaries of Tibet in comparison to geologic observations made from the interior. I have conducted neotectonic studies in the vicinity of the Karakoram-Jiali fault zone (KJFZ) to estimate the finite and instantaneous strain fields related to the Indo-Asian collision.; This study reveals a system of conjugate strike-slip faults and associated north-striking normal faults with a spacing of ∼150 km along the KJFZ. The conjugate faults merge with the Bangong-Nujiang suture zone and are comprised of NE-striking left-slip faults to the north and NW-striking right slip faults to the south. The magnitude of displacement reveals ∼12 km of fault slip for each branch of the conjugate strike-slip faults. Integrating the E-W and N-S components of finite strain associated with the conjugate faults is ∼65 and ∼12 km, respectively. If one includes the minimum displacement of the Karakoram fault, the E-W component of finite strain is >100 km. Additional brittle structures related to the Indo-Asian collision include west-dipping normal faults that are located near the intersection of the strike-slip faults that bound topographic depressions. This region coincides with the location of the Bangong-Nujiang suture zone, and suggests that active basin development along this Mesozoic suture may be related to the geometry of the conjugate strike-slip faults. This relationship implies an area increase of Tibet, and is consistent with a constrictional strain field. More importantly, the results indicate that E-W extensional strain is dominant over N-S contraction.; The instantaneous strain associated with the conjugate fault systems was determined using InSAR. The data indicates that N-S contraction and E-W extension is accommodated by the conjugate strike-slip faults. This is consistent with the long-term behavior of the fault systems. In terms of fault kinematics, while one segment of the conjugate fault system is accumulating elastic strain, its conjugate does not do so within the time span of the data and the detection limit of the technique. An unresolved problem is the mechanism for initiating the odd geometry of conjugate strike-slip faults in Tibet.