Solubility of water in the α, β and γ phases of (Mg,Fe)2SiO4

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doi: 10.1007/s004100050161
Authors:Kohlstedt, D. L.; Keppler, H.; Rubie, D. C.
Author Affiliations:Primary:
Universitat Bayreuth, Bayreuth, Federal Republic of Germany
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 123(4), p.345-357. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1996
Note:In English. 39 refs.; illus., incl. 1 table
Summary:The solubility of hydroxyl in these three phases of (Mg,Fe)2SiO4 was investigated by hydrothermally annealing single crystals of San Carlos olivine. Experiments were performed at T of 1000 or 1100°C under a confining P of 2.5 to 19.5 GPa in a multi-anvil apparatus with the fO2 buffered by the Ni:NiO solid-state reaction. Hydroxyl solubilities were determined from IR spectra obtained of polished thin sections in crack-free regions up to 100 µm in diameter. In the α-stability field, hydroxyl solubility increases systematically with increasing confining P, reaching a value of ∼ 20 000 H/106Si (12 wt.% ppm H2O) at the α-β phase boundary near 13 GPa and 1100°C. In the Γ field, the solubility is ∼ 450, H/106Si (27 000 wt.% ppm H2O) at 19.5 GPa and 1100°C. The observed dependence of hydroxyl solubility with increasing confining P in the α phase reflects an increase in water fugacity with increasing P moderated by a molar volume term associated with the incorporation of hydroxyl ions into the olivine structure. These data demonstate that the entire present-day water content of the upper mantle could be incorporated in the mineral olivine alone; therefore, a free hydrous fluid phase cannot be stable in these regions of the upper mantle with a normal concentration of hydrogen. Free hydrous fluids are restricted to special tectonic environments, such as the mantle wedge above a subduction zone. [P.Br.]
Subjects:Fugacity; Geochemistry; Hydroxyl ion; Iron silicates; Magmas; Magnesian silicates; Mantle; P-T conditions; San Carlos Olivine; Silicates; Solubility; Upper mantle; Water
Abstract Numbers:96M/4180
Record ID:1996073492
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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