The Dhaulagiri Transtensional Zone: an active fault zone within the Western Nepal Himalaya
Field mapping and remote sensing in the Dhaulagiri Range of Nepal reveal a regionally extensive active fault zone linking the Tibrikot Fault to the Dhaulagiri Southwest Fault, herein termed the Dhaulagiri Transtensional Zone [DTZ]. Right and normally offset Quaternary features exist along the extent of the DTZ. Field investigations at key sites constrain the local geometry, kinematics, and magnitude of slip. The DTZ accommodates slip along two strike-slip faults striking N40-50W with an extensional right step-over striking N10-20E. Dextral slip is interpreted to decrease from northwest to southeast, 650 m to 450 m respectively. The DTZ is indicative of the most recent deformation processes in western Nepal, postdating other structures in the region. Oblique slip along dextral fault segments as well as linkage to dip-slip structures suggests the DTZ accommodates strain both parallel and orthogonal to the Himalayan arc. This normal/strike-slip strain is thought to be accommodated either synkinematically along the DTZ extent or cyclically with high frequency at this stage of Himalaya growth. On the basis of geometry, kinematics, and structural position we correlate the DTZ to active faulting along the Karakoram Fault, the Gurla Mandhata-Humla fault systems, and the Dhaulagiri Southwest Fault. This suggests a 350 km long right-slip fault system across the Western Nepal Himalaya. This, now contiguous, regionally extensive system lies between active north-south compression at the toe of the Himalayan thrust wedge and east-west extension in its hinterland (Tibetan Plateau). We interpret this system to operate as a transitional margin between the differing styles of deformation. Future evolution of the system into a through-going discrete structural feature suggests the possible formation of a forearc sliver, partitioning strike-slip strain from the obliquity of convergence away from other regional dip-slip structures.