The water content of olivines from the North Atlantic Volcanic Province

The water content of olivine crystals from picrites and basalts from the North Atlantic Volcanic Province has been estimated using non-polarised Fourier transform infrared spectra. H₂O concentrations vary from about 18 ppm by weight to below the detection limit of ca. 0.5 ppm. The most H₂O-poor olivines (≤0.5 ppm H₂O) probably reflect olivine crystallisation or re-equilibration at shallow crustal levels, possibly after magma degassing. However, some of the Mg-rich olivines (Fo_87-91.5) have elevated H₂O contents (3-7 ppm) and indicate the presence of mantle source regions with >300 ppm H₂O for any reasonable crystallisation depth. The elevated H₂O content may be sufficiently high to significantly affect the mantle viscosity and melting behaviour and thus contribute to the simultaneous production of melt over a vast area from Baffin Island to the British Isles at 58-62 Ma.