LAUSR

Abstract Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, mantle composition, and related physical properties. Most mantle lithologies (peridotite) contain little water (~50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous (~300 ppm) relative to the mantle rocks. Pyroxenites also melt at lower temperatures than peridotites and are thus important to magma genesis. Thus, quantifying pyroxenite water contents provides new information on the distribution of water in the mantle. Here, we present phase-specific FTIR measurements of the water contents in pyroxenite mantle xenoliths from two continental lithospheric domains that experienced intense metasomatism: the French Massif Central (FMC, France) and the Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet pyroxenites are more hydrated ([H2O]Clinopyroxene = 386–685 ppm; [H2O]Orthopyroxene = 124–155 ppm; [H2O]Garnet