Composition, alteration, and origin of the basement lavas and volcaniclastic rocks at Site 738, southern Kerguelen Plateau

Abstract

During ODP Leg 119 one basement hole was drilled at Site 738. The 38.2m of basement rocks drilled comprises three basaltic aa-lava flows with basal and top breccies, overlain by Turonian marine carbonates. Site 738 basalts probably erupted near a fracture zone, and were emplaced during the plateau-forming stage of Kerguelen Plateau evolution under quiet, subaerial to shallow water conditions. The basalts are T-MORB, chemically resembling Mesozoic continental flood basalts of the southern hemisphere. Two slightly different magma batches are distinguished by Fe, Ti, Al, Zr, and REE concentrations. Prior to eruption, the magmas had undergone significant olivine and some clinopyroxene fractionation. A saponite-celadonite secondary mineral assemblage confines the alteration temperature to <170°C. -from Authors