Fluid genesis through serpentinites and the origin of subsurface electrical conductors in Northwest India and adjoining regions

Abstract

Large-scale conductivity anomalies have been detected and subsequently modelled/inverted based on the data of geomagnetic deep sounding in Northwest India by various researchers. In this study, by analytical dissection of several other geophysical parameters, in conjunction with the constrained modelling of electrical parameters of the conductors, we believe that we have resolved the origin of three Northwest Indian conductors. This issue had remained, so far, either speculative or an explanation was given without taking due analytical support from other geophysical data. Moreover, a unique relationship has been found and the same advocated amongst the high values of Poisson’s ratio and the electrical parameters of conductors. These high values of Poisson’s ratio conform to the presence of serpentinites in the region at appropriate depths. Under the present geotectonic setting, the upward migration of serpentine from mantle to subcrustal level and its consequent dehydration leading to fluid genesis seems to be the appropriate cause for the conductivity anomalies in the Northwest Indian region, including Lesser Himalaya, however, the exact mechanism for upward migration (a fact established elsewhere) may, at present, remain tentative. Some indirect inferences have been drawn through a hypothesized model (cartoon) to shed light on the possible mode of fluid transport resulting in conductivity anomalies of the region. The presence of fluids has also been cited in literature in Higher Himalayan regions, resulting due to under-thrusting of the Indian basement. Elsewhere in the Northwest Himalayan region, the presence of serpentinite in close association of eclogite has been found. These serpentinites are formed by hydration of the mantle wedge resulting due to de-watering of the subducted slab. These facts strengthen the belief of the continuation of fluid body in Himalayan and adjacent Northwest region in the crust.