DUNITIFICATION OF MANTLE LITHOSPHERE BELOW THE SOCIETY ARCHIPELAGO - EVIDENCE FOR MAGMA-MANTLE THERMAL AND CHEMICAL TRANSFERS THROUGH XENOLITHS FROM THE PAPENOO VALLEY, TAHITI

Chemical and thermal transfers between mantle lithosphere and O.I.B. from French Polynesia are described in an inclusion suite from the Papenoo Valley, Tahiti. The methods used consider chemical exchange kinetics in geothermometry and olivine deformation study. The mineralogical study shows the extent of the chemical and thermal exchanges between a lithosphere equilibrated at 1000-1050-degrees-C and plume basalts whose liquidus temperature is about 1250-degrees-C. The dunitification process along with the spinel and olivine "fertilization" is revealed in samples which preserved features of their former mantle deformation. The deformation study also shows that interaction took place within the mantle itself. The whole of the results implies a significant metasomatism of the mantle lithosphere and alteration of the initial geochemical signature of the deep originating O.I.B. beneath French Polynesia.