Abstract

Bouguer anomaly map of Saurashtra, prepared from the high precision detailed gravity data, depicts several highs and lows of varying wavelength and amplitudes. The large amplitude circular gravity highs are associated with known volcanic plugs of Deccan magmatism. However the most significant feature of the Bouguer anomaly map is the presence of a large wavelength gravity low centered over Jasdan plateau, which bears an inverse relation with the topography and may be related to crustal thickening due to isostasy. An unbiased estimate of isostatic regional based on zero free air anomalies shows large wavelength circular gravity low of 25 mGal in this region. Modelling of regional isostatic anomalies using constraints from DSS studies reveals presence of anomalous thick crustal root in Saurashtra. The residual anomaly map of Saurashtra peninsula obtained after subtracting the isostatic regional from the observed field still shows large wavelength gravity low over the eastern part besides several medium to small amplitude gravity lows. The large wavelength residual gravity low appears to be the result of mass deficiency in the upper mantle beneath the Cambay region, which also coincides with the low velocity zone observed in seismic tomography experiments. The small wavelength gravity lows are interpreted due to sediments below the trap, which is clearly brought out along Lodhika-Dhanduka and Kuranga-Latipur profiles. The later shows thickest sediments present in Saurashtra.