Water storage in cratonic mantle

Abstract

AbstractKnowledge of the water capacity of the deep lithosphere is crucial for validating models of craton growth and for constraining solid earth volatile cycles over geologic time. However, experimental constraints on water solubility and partitioning often disagree with natural rock data. We present a bulk compositionally dependent model of water storage capacity in pyrolite over a range of lithospheric mantle pressures and temperatures. Models are compared against published xenolith nominally anhydrous mineral (NAM) water contents, which have been recalculated to reflect the last water content of the mantle lithosphere by using coexisting pyroxene water contents in the same samples. Our main findings are that (1) regardless of tectonic setting, olivine records similar recalculated water contents, suggesting a common level of water undersaturation in the lithospheric mantle, and (2) equilibrium water partitioning between clinopyroxene and orthopyroxene (Dcpx/opx) increases down‐temperature. We propose these trends may be explained by re‐hydration/re‐fertilization of cratonic mantle early during coalescence, followed by cooling‐induced water exsolution from orthopyroxene and garnet formation as cratons thicken and stabilize.