A Global Analysis of the Oxygen Isotope Composition of Basalts: Evidence for Low and High 18O Reservoirs in the Mantle

It is now well established that the mantle is compositionally heterogeneous on a variety of scales. The ultimate cause for these heterogeneities is the recycling of continental and oceanic crust via subduction into the mantle. Stable isotope studies have the potential to make important contributions to studies of mantle heterogeneity, but their application has lagged behind radiogenic isotopes. In this contribution we examine oxygen isotope variations in basalts and discuss their causes. Oxygen isotopes are strongly fractionated during low-temperature processes such as weathering and hydrothermal alteration. Therefore, subduction related processes should provide an effective mechanism of introducing oxygen of variable composition into the mantle.