Petrology of Offshore Basalts of Bombay Harbour Area, West Coast of India

Abstract

Recent marine geological and geophysical surveys indicate that the Deccan Traps extend to the offshore area of Bombay. Cores from bore holes in Deccan Traps collected from Bombay Harbour have been classified as basalts, olivine basalts, spilitic basalts, and dolerites. Plagioclase composition of basalts ranges from An72-60 to An40-45 (while in spilitic basalts it is in the range of 10-32U+0025); augite (2Vz = 30 degrees - 50 degrees), fresh and altered olivine with ubiquitous magnetite and devitrified glass are conspicuous. The chemical data indicate that the basalts are tholeiitic. Secondary minerals encountered support the view that the basalts are spilitised. Basalts of this area show affinities to both continental and oceanic types especially in the abundances of TiO2 (1.21-2.51U+0025), and therefore may be of transitional nature.