Spatial and Temporal Characteristics of Deformation along the Karakoram Fault System, Western Tibet

To better understand the structural development of releasing bends along the Karakoram fault and its cumulative slip history, we investigated the interaction between basin-bounding faults and basin fill of the southern Gar basin, one of only two known releasing double-bend basins along the fault. Field relationships indicate the basin is bounded by a N-NW-striking E-dipping master normal fault that merges with NW-striking right-slip faults. The master fault displays older striations which indicate right-slip. This fault and others in the area are oriented ~20-15° clockwise from the active PDZ. Another prominent set of structures are oriented ~20-15° counterclockwise from the active PDZ. Based on the kinematics we interpret them to have evolved as Reidel (R) faults in a distributed simple shear zone which we estimate to be 50-35 km wide. The later phase of normal dip-slip can be explained by linking of the PDZ to the R faults causing a change in the style of deformation to dominantly extensional. Folding of the basin fill suggests a listric fault at depth. We explain this style of deformation and history via a model that calls upon reactivation of R shears at shallow levels in the crust (low confining pressures), while at deeper levels in the crust these faults merge with the PDZ forming an extensional flower structure. Forward modeling of the master fault system shows the basin accommodates 8 km of east-west extension during the second phase of deformation. Based on the structural relationship to the adjacent Ayi Shan detachment, the system may accommodate 10's of kilometers of extension. Based on restoration of R shears on either side of the basin we estimate 55 km of right-slip along the Karakoram fault. We interpret that the system evolved from an en echelon configuration to a through-going linked system of P and R faults.