Active morphogenic faulting and paleostress analyses from the central Nahan Salient, NW Siwalik Himalaya

Tectonics of ancient foreland basins of collisional orogens are of enormous international attention from the perspectives of applied (e.g., hydrocarbon exploration) and theoretical geosciences (e.g., tectonic models). Morphogenic faulting produces identifiable surface morphology and structural patterns that provide vital insights for reconstructing paleostress scenarios and the present-day surface topography. The principal stress directions that affected the region are important to understand the polyphase tectonic zones. We perform geomorphic analyses and combine them with paleostress analysis of mesostructures from the Panchkula-Morni region from the central Nahan Salient. We reconstruct the orientation of the principal stress axes that evolved during the tectonic evolution of the brittle sheared sandstones of the Lower/Upper Siwalik units. Three deformation phases are determined that are interpreted to be coeval with the Himalayan orogeny: (i) extensional stress field with NW oriented extension, (ii) extensional stress field with NE–ENE oriented extension, and (iii) NE-directed compression. Out of these, component (iii) led to the uplift of the Himalayan orogen and produced the present-day topography. Slickenside kinematic indicators viz., PT, RM and PO structures helped in interpreting the movement of the slip planes exposed in the uniform lithology. Compressional stress field with NE compression is consistent with the geometry of the Bisiankanet Thrust (BkT) inferred from geomorphic analyses. The NE extension direction and oblique plunge of the σ 1 -axis may be responsible for the oblique movement with major normal slip at the western extremity of the BkT. Abrupt change in topographic swath profiles, their mutual offset in the hangingwall and knickpoint migration indicate active uplift especially across the newly identified out-of-sequence Tikkar Tal Thrust (TTT) on the map and also on an existing seismic section.