The Occurrence of Acid and Intermediate Rocks in the Deccan Volcanic Province with Associated High Positive Graity Anomalies and their Probable Signficance

Abstract

The occurrence of intermediate and acid rocks such as trachyte and rhyolite are known to occur mainly along the west coast around Mumbai and in the Saurashtra area, such as in Girnar, Barda, Osham and Alech hills. There are also other isolated occurrences in Phenai Mata region and Pavagadh hill (Sethna, 1989). It is interesting to note that both along the west coast near Mumbai and in the Saurashtra area there are occurrences of relatively high positive gravity anomalies of up to +70 m Gal Bouguer anomaly (Negi et al. 1992). It seems unlikely that such a close spatial relationship of these anomalies, and the occurrence of more evolved rock types could be entirely fortuitous. Whilst, intuitively, negative gravity anomalies might be expected in areas where less dense, evolved rocks occur, thought should be given as to the petrogenesis and possible origin of these evolved rocks.