Geomorphic evidences of active faulting in the northwestern Ganga Plain, India: Implications for the impact of basement structures

摘要

Active faults of the densely forest covered northwestern part of the Ganga Plain have been identified and mapped on the basis of geomorphic signatures as observed in the Digital Terrain Models, remote sensing data and field. The structural limit between the Ganga Plain and Himalaya in the north is defined by the Himalayan Frontal thrust (HFT), which is a direct consequence of the compression resulting from collision of Indian and Eurasian plates and present day principal displacement zone between them. This HFT is offset by dip-slip, oblique-slip and strike-slip faults, extending transversely through the Ganga Basin. Analysis of these faults in conjunction with the available geological and subsurface geophysical data reveals that the development of some of these transverse faults is localized along basement highs of the basin. These faults tear asunder the Himalayan thrust sheets and may have developed during the collision either because of a rheological contrast between the basement highs and adjacent sedimentary fill, or a lateral change in cover thickness across the basement highs, or due to the reactivation of pre-existing basement faults. The continuous pressing and prodding by these basement highs have caused bending of the strata, leading to conspicuous bending of the mountain belt. One of the tear faults has formed as a result of the along-strike propagation of an oblique ramp of the Main Boundary thrust (MBT), along which the Lesser Himalayan succession is thrust over the Siwalik. In addition to these tear faults, some transverse faults of limited lateral extent, cutting through the mountain belt and basin, may have formed during the last event of deformation along the HFT zone.