High-temperature experiments on silicate melt inclusions in olivine at one atmosphere. Inference on temperatures of homogenization and H2O concentrations
A series of heating stage experiments, at ambient atmosphere and high temperature, were conducted in order to detail the change in the homogenization temperature and the behavior of H2O of melt inclusions in olivine phenocrysts (Fo82-89). The samples were collected at different volcanic sites (Piton de la Fournaise, Réunion island; Stromboli, Aeolian islands; FAMOUS zone) expected to have a range of magmatic water contents. The melt inclusions vary in composition from basaltic to shoshonitic, with H2O contents from 0.14 to 2.9 wt.%. Temperatures of homogenization (Th) of melt inclusions systematically increase with time during heating experiments, regardless their major element composition and their H2O. It is proposed that Th changes with time in response to deformation of the host crystal and change in the volume of the cavity. The FTIR spectra successively acquired on the same inclusion repeatedly heated at constant temperature clearly demonstrated that the relative absorbance (Abs.n/Abs.0) measured at 3535 cm-1 corresponding to hydroxyl group and molecular H2O decreases with time. The H2O-rich melt inclusions may have lost from 20 to 80% H2O after the first homogenization and almost total dehydration of melt inclusions may occur within few hours or less, at one atmosphere. Water loss driven out off olivine-hosted melt inclusions possibly exists to some extents in natural large dunitic bodies or in mantle xenoliths.
Laboratoire Pierre Süe, CEA-CNRS, CE-Saclay, 91191 Gif sur Yvette, France
Chemical Geology 2002, 183, 87-98