Abstract
Sections of Ontong Java Plateau basalt basement in central Malaita (Solomon Islands) are 0 times 5-3 times 5 km thick and resemble a much-expanded version of that recovered at Ocean Drilling Program Site 807. super(40)Ar- super(39)Ar ages (121-125 Ma) are identical to those for Site 807, southern Malaita, Ramos Island, parts of the island of Santa Isabel, and Deep Sea Drilling Project Site 289; the similar to 90 Ma eruptive episode seen in Santa Isabel, San Cristobal, and at drill sites 803 and 288 is not represented. The central Malaitan basalts provide further evidence of two distinct ocean-island-like mantle sources, and the combined data preclude a significant contribution from normal ocean-ridge-type mantle. As at Site 807, two geochemically distinct stratigraphic groups are present, the Singgalo Formation ( similar to 750 m thick in central Malaita) and the Kwaimbaita Formation (>2700 m thick). Both a peridotite plume-head and eclogite-bearing plume-head may account for the geochemical characteristics, but the observed stratigraphic succession requires special conditions for the latter model. A number of first-order features of the Ontong Java Plateau do not obviously fit the predictions of any plume-head model: for example, at least two important, geochemically similar eruptive episodes similar to 30 my apart, the lack of an obvious plume-tail trace, and lack of evidence for emergence or significant uplift.