On the basis of present study, it is concluded that the deep crustal structure of passive continental margins is best interpreted with the help of geophysical methods such as deep seismic reflection, seismic refraction, gravity, and magnetic data. The results from these methods are combined to obtain a geologically plausible model from the deep crustal structure.
In the present study an integrated interpretation of the results obtained from gravity, magnetic, bathymetry and deep seismic reflection data sets was used to develop the deep crustal picture of Indus offshore basin beneath the seismic line PC/9074-86. This deep seismic profile, running across the continental margin (northeast - southwest), suggests a maximum sediment thickness greater than 10 Km to the west of Base Tertiary hinge zone i.e., in the offshore "depression area". The deeper (6 sec twt) parts of the seismic section do not show any evidence of discontinuous seismic events in the extensional regime of the Indus offshore, which is most possibly due to extra-thick sedimentary sequence above the acoustic basement, and weak energy source used in the seismic survey.
Steep positive gravity gradient towards southwest of the well PakCan-1, above thick sedimentary strata (greater than 10 Km), is attributed to a prominent rise in the mantle. Intuitively, extending the depth model beyond the present day shelf break and computing its gravity indicates that the overall gravity effect is one of the typical shelf edge anomalies. Furthermore, it is speculated from the 2D-modelling of free-air gravity anomalies along the seismic line PC/9074-86 that the area to the west of the Base Tertiary hinge zone suffered maximum crustal attenuation (approximately 24.5 Km thick crust towards north-east is reduced to 6.5 Km on the mantle rise) and this could be one of transitional crustal regions formed during the rifting phase of the margin development. It is further speculated that in the outer shelf regions, where upper mantle rocks are shallower, overall geothermal gradients are expected to be higher than the innermost shelf regions. It is also interpreted that the younger sediments in the offshore area may have attained maturity due to thinning of the crust and consequent rise of mantle in the outermost shelf regions and may produce hydrocarbons.