Arc-Parallel Shear and Orogenic Deformation Along the Oblique Himalayan Convergent Plate Margin: Implications from Topographic- and Gradient-Anomaly Profiling in the Himalaya

GNSS measurement-based geodetic studies have led to researchers explaining the regional deformation in the Himalaya in terms of arc-parallel shearing and arc-normal compression. Arc-parallel extension is caused by an increase in the shearing rate, which is reflected in the increasing arc-parallel velocities as one moves along-arc away from the arc-center. This has prompted many to recognize the significance of arc-parallel shearing and extension in the Himalayan orogeny. Several researchers have proposed that the arc-parallel deformation is taken up almost entirely by the Karakoram fault system through slip transfer from the Himalayan foothills, though recent studies have provided some evidence of dextral faulting within the Northwest (NW) Himalayan accretionary wedge. In this paper we address this issue by providing topography-derived evidence such as the deviation of the maximum gradient azimuth from the arc-normal along the Himalayan arc to show that obliquity in convergence is a significant controlling factor in shaping the morphology of the Himalayan slopes. Approximately 4 ± 3 mm/year of arc-parallel dextral shear is being accommodated within the accretionary wedge spanning the NW Himalaya (particularly the part in Himachal and Garhwal), which is approximately 55% of the total arc-parallel dextral shear resulting from the ongoing convergence between southern Tibet and the Indian Plate in this portion of the Himalaya. The study further suggests consistency of the observed Himalayan deformation with the oblique convergence model and the significant role that the underthrusting ridges inherited from the Indian Plate are playing in the strain accommodation pattern in the overlying Himalaya.