Mantle metasomatic influence on water contents in continental lithosphere: New constraints from garnet pyroxenite xenoliths (France & Cameroon volcanic provinces)

Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, composition, and related physical properties. Most lithologies (peridotite) contain little (~50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous (~300 ppm) relative rocks. Pyroxenites also melt at lower temperatures than peridotites thus important magma genesis. Thus, quantifying pyroxenite provides new information on distribution mantle. Here, we present phase-specific FTIR measurements xenoliths from two continental domains that experienced intense metasomatism: French Massif Central (FMC, France) Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet hydrated ([H2O]Clinopyroxene = 386–685 ppm; [H2O]Orthopyroxene 124–155 [H2O]Garnet < 0.5 FMC ones 112–465 61–104 ppm). These concentrations homogenous grain correlate with equilibrated major element concentrations, indicating they representative water, although were dehydrated during metasomatism by a carbonatitic fluid (based correlation between LaN/SmN Ti/Eu ratios); likely not affected metasomatism. show peculiar spectra may reflect preferential dehydration specific sites pyroxene structure. In both regions, modified light rare Earth (e.g., Ce) pyroxenites, resulting highly variable H2O/Ce ratios. Therefore, conclude utility ratio identify involvement magmas genesis limited.