Implications for the lithospheric structure of Cambay rift zone, western India: Inferences from a magnetotelluric study

Broad-band and long-period magnetotelluric (MT) data were acquired along an east-west trending traverse of nearly 200 km across the Kachchh, Cambay rift basins, and Aravalli-Delhi fold belt (ADFB), western India. The regional strike analysis of MT data indicated an approximate N59 degrees E geoelectric strike direction under the traverse and it is in fair agreement with the predominant geological strike in the study area. The decomposed transverse electric (TE)- and transverse magnetic (TM)-data modes were inverted using a nonlinear conjugate gradient algorithm to image the electrical lithospheric structure across the Cambay rift basin and its surrounding regions. These studies show a thick (similar to 1-5 km) layer of conductive Tertiary-Mesozoic sediments beneath the Kachchh and Cambay rift basins. The resistive blocks indicate presence of basic/ultrabasic volcanic intrusives, depleted mantle lithosphere, and different Precambrian structural units. The crustal conductor delineated within the ADFB indicates the presence of fluids within the fault zones, sulfide mineralization within polyphase metamorphic rocks, and/or Aravalli-Delhi sediments/metasediments. The observed conductive anomalies beneath the Cambay rift basin indicate the presence of basaltic underplating, volatile (CO2, H2O) enriched melts and channelization of melt fractions/fluids into crustal depths that occurred due to plume-lithosphere interactions. The variations in electrical resistivity observed across the profile indicate that the impact of Reunion plume on lithospheric structures of the Cambay rift basin is more dominant at western continental margin of India (WCMI) and thus support the hypothesis proposed by Campbell & Griffiths about the plume-lithosphere interactions.