The Late Eocene‐Early Miocene Unconformities of the NW Indian Intraplate Basins and Himalayan Foreland: A Record of Tectonics or Mantle Dynamics?

Abstract A well‐developed late Eocene to Miocene unconformity, termed the base Miocene unconformity (BMU), is found throughout the intraplate basins of northwestern India and has previously been ascribed to Himalayan tectonics. This hypothesis is investigated by first describing the nature and age of the BMU in the northwest (NW) Indian intraplate basins and then reconstructing the location of the BMU relative to the Himalayan deformation front at the time it formed. We suggest that formation of the BMU in western India cannot be related to Himalayan tectonic processes associated with plate loading and flexure unless the Indian plate had an elastic thickness of >125 km, which is highly unlikely. Furthermore, the resumption of deposition post unconformity rules out inversion due to compression associated with India‐Asia convergence as a cause, as these compressive forces are still present. We note the coeval nature of the unconformity in the NW Indian plate intraplate basins and the Himalayan peripheral foreland basin. If the unconformities of the Himalayan peripheral foreland basin and the NW Indian intraplate basins were formed by a common process, uplift due to circulation in the mantle is the only possible regional‐scale mechanism. Such circulation could be the result of the intrinsically time‐dependent high‐Rayleigh number convection in the mantle, which has resulted in well‐documented unconformities elsewhere, or be the result of subducting slab break‐off beneath the Himalaya.