Magnetotelluric evidence for an Archaean – Proterozoic lithospheric assemblage within the Cambay rift basin, western India, and its role in channeling of plume-derived fluids within the basin

Abstract The Cambay rift basin (CRB) in western India is a hydrocarbon producing basin, which has been extensively explored geophysically for hydrocarbon reserves. However, only a limited number of geophysical studies have been carried out to image its lithospheric structure. We have conducted a magnetotelluric (MT) study along an E-W profile across the CRB to delineate its lithospheric structure. The profile starts from the eastern part of the Kachchh rift basin (KRB) to the west of the CRB and extends up to the Aravalli-Delhi fold belt in the east. MT data were acquired at 26 sites along this 210-km-long profile and cover a wide period range of 0.0026–30,000 s. Two-dimensional inversion of this dataset yields a geoelectrical model that reveals a spatially heterogeneous lithosphere in the basin. We infer that the western highly resistive and the eastern moderately resistive blocks represent an Archaean depleted and a Proterozoic lithosphere, respectively. It is postulated that the weak Proterozoic lithosphere facilitated channelization of exsolved fluids and volatile enriched (CO2, H2O) melts to the crustal depths and lithospheric alteration of the eastern block during its interaction with the Reunion plume. The thickness of the sedimentary basin in the CRB also varies between ~2 to 7 km, the thickest part being in the western block. In contrast, the basin is less than 2 km thick in the KRB.