Regional conductance map of Saurashtra and surrounding regions

Magnetovariational fields recorded by an array of magnetometers in Saurashtra and the surrounding regions have been analysed to infer the electrical conductivity distribution of the region. Only night-time magnetovariational fields were used because of the prevailing uniform source field conditions. Induction arrows (showing the relationship between vertical and horizontal magnetic field variations) are pointing towards Saurashtra and Kutch offshore basins. Thin-sheet modelling of the observed induction arrows suggest the presence of two prominent conductivity anomalies. The first elongated anomaly coincides with the horst and graben offshore structures of Saurashtra and Kutch. The second anomaly is over the Saurashtra depression and correlates well with the low-magnetization anomaly that extends in the NE–SW direction towards Cambay basin. The possible cause for the above anomalies may be fluids originated by underplating mantle material related to hotspot activity and rift phase volcanism. Large-scale upwelling, partial melts or thermal remobilization of crustal and mantle material during the processes of rifting and hotspot activity may enhance crustal/upper mantle conductivity, which explains the accentuation of the induction arrows observed in Saurashtra region.