The water content of olivines from the North Atlantic Volcanic Province

The water content of olivine crystals from picrites and basalts from the No rth Atlantic Volcanic Province has been estimated using non-polarised Fouri er 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 oliv ines (less than or equal to 0.5 ppm H2O) probably reflect olivine crystalli sation or re-equilibration at shallow crustal levels, possibly after magma degassing. However, some of the M-rich olivines (Fo(87-91.5)) have elevated H2O contests (3-7 ppm) and indicate the presence of mantle source regions with > 300 ppm H2O for any reasonable crystallisation depth. The elevated H 2O content may be sufficiently high to significantly affect the mantle visc osity and melting behaviour and thus contribute to the simultaneous product ion of melt over a vast area from Baffin island to the British Isles at 58- 62 Ma. (C) 2001 Elsevier Science B.V. All rights reserved.