Basalts and related rocks from deep-sea drilling sites in the Central and Eastern Indian Ocean

Abstract

Petrological and geochemical data are presented for basement rocks recovered from thirteen sites (211, 212, 213, 214, 215, 216, 253, 254, 256, 257, 259, 260 and 261) drilled on Legs 22, 26 and 27 of the Deep Sea Drilling Program. Basalts from Sites 212, 213, 253, 257, 259 and 261 have petrographic and geochemical characteristics of tholeiitic basalts from active spreading ridge axes in the major ocean basins. Except for the lower basalts at Site 253, all the basement rocks from four Ninetyeast Ridge sites (214, 216, 253, 254) are similar to oceanic island tholeiitic sequences such as on Amsterdam—St. Paul Islands. The geochemical data for the Ninetyeast Ridge rocks are consistent with the development of this ridge as a hot-spot trace. Basalts from deep ocean Sites 216 and 256 have geochemical characteristics more akin to tholeiitic basalts from spreading ridge axes close to major volcanic islands, i.e. they have high large ion lithophile element abundances relative to tholeiitic basalts found at spreading ridge axes away from islands. Alkali olivine basalts were recovered from Site 211 and they contain abundant amphibole. They are related to the volcanism which created the Cocos—Keeling—Christmas shoal areas.