Host: Japan Association of Mineralogical Sciences
Combined thermobarometric and Os isotopic data for peridotite xenoliths carried in alnöite intruding crust on the Ontong Java Plateau reveal that the basal section of subplateau lithospheric mantle (95-120 km) includes pieces of mantle with unradiogenic 187Os/188Os ratios as low as 0.1156, which give Proterozoic model ages down to ∼1.8 Ga. In contrast, shallower portions (<95 km) yield a restricted range of 187Os/188Os ratios from 0.1223 to 0.1272, illustrating an affinity with modern abyssal peridotites. This contrasting Os isotope data between shallow and deep portions suggest their derivations from different reservoirs. We infer that the subplateau lithosphere forms a genetically unrelated two-layered structure, comprising shallower oceanic lithosphere and deeper impinged material, which involved a recycled Proterozoic lithosphere as heterogeneous components.
