Geology of Mumbai and Surrounding Areas and its Position in the Deccan Volcanic Stratigraphy, India

Field data reveal that the lava flows in Mumbai and surrounding areas erupted after the rifting of the main plateau basalts of the Deccan Volcanic Province. Majority of the lava flows occur as subaqueous lavas forming hyaloclastites, spilitic pillow lavas and partially subaqueous and subaerial flows. The basic lavas are associated with rhyolitic flows and contemporaneous intrusions of basic and trachytic magmas forming hybrid rocks of monzonitic and dioritic variety. It has been shown that petrochemically the basic magma of the area is very different from the magma types associated with the mainland horizontal flood basalts ofthe Deccan Volcanic Province. The basic rocks of the Mumbai-Salsette area show lower concentrations of Cr, Ni, Y, V and Ti; and higber concentrations of K, Rb, Ba, Zr and Nb. Majority of these samples contain similar concentrations of phosphorus except for three Salsette samples which show unusual high values. The volcanics of the Mumbai-Salsette area are classified as forming the Salsette Subgroup with three Formations viz., Mumbai Island, Madh-Utan and Manori.