Abstract:
The Kachchh and Cambay rift basins are two pericontinental rift basins at the western continental margin
of India (WCMI), which evolved during different
stages of the Mesozoic era. Magnetotelluric measurements were carried out at 68 stations along four east–
west trending profiles across these basins with an aim
to infer basement configuration and sediment thickness. The data were analysed for galvanic distortions
and decomposed into transverse electric (TE) and
transverse magnetic (TM)-modes by rotating the impedance tensor into corresponding geoelectric strike
directions of the four profiles. The decomposed data
responses were then inverted using a nonlinear conjugate gradient algorithm. The top conductive layers
(~2500–7500 S) across the Kachchh and Cambay rift
basins indicate the presence of Cenozoic sediments
and Deccan traps, which corroborates the results of
earlier geophysical studies across these basins. The
sediment thickness is low across Diyodar and Tharad
ridges compared to the Sanchore, Patan and Mehsana
sub-basins. A high conductive zone near Mehsana
may support the evidence for the presence of Mesozoic
sediments beneath traps as inferred from a deep seismic sounding (DSS) study. Even though the Oil and
Natural Gas Corporation Limited (ONGC) drilled
wells and DSS study reported the presence of Mesozoic sediments beneath the traps near Tharad ridge,
their presence here is not clear from this study. Igneous intrusives and a Precambrian Aravalli–Delhi fold
belt are delineated on either side of the Cambay rift
basin. The electrical resistivity variations across these
basins lead to the inference that the subsurface structure is highly heterogeneous in nature due to faults
within the rift basins.
