Transverse Faizabad Ridge in the foreland Ganga basin: A mosaic of fragmented crustal blocks as revealed by magnetotellurics

Abstract

The Ganga basin bordering the central segment of the Himalayan arc hosts several buried transverse ridges, which are considered to have significant influence on the Himalayan seismicity and tectonics. Information on the nature of crustal structure, composition and spatial heterogeneities of these ridges is elusive. The Faizabad Ridge is one such prominent ridge, considered to be subsurface northward continuation of the Bundelkhand craton. We have carried out a magnetotelluric (MT) study along a 335-km-long profile covering this ridge to delineate its crustal structure. The two-dimensional geoelectric model of the crust and sub-crustal lithosphere suggests that the Faizabad Ridge is constituted of at least three resistive crustal blocks rather than a single unit. Moderate conductivity zones bounding these blocks broadly coincide with the locations of major rivers implying that these rivers follow the geological trend of the buried conductive zones. A major conductive zone at the southern end of the profile marks the lithospheric contact between the exposed Bundelkhand craton and a Proterozoic mobile belt. The post-collision sedimentary succession above the Ridge forms a smooth layer that thickens northward and attains a thickness of about 6 km at the Himalayan foothills. Our results rule out northward progression of the Faizabad Ridge into the Himalaya along its NNE strike. In conjunction with seismically derived depth of the acoustic basement along the Himalayan arc in Nepal, our results imply that the Faizabad Ridge, if it continues up to the Himalaya, possibly takes a westward turn north of Faizabad.