High pressure fluids in the system MgO-SiO2-H2O under upper mantle conditions

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Authors:Stalder, R.; Ulmer, P.; Thompson, A. B.; Günther, D.
Author Affiliations:Primary:
ETH Zentrum, Institut für Mineralogie und Petrographie, Zurich, Switzerland
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 140(5), p.607-618. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:2001
Note:In English. 33 refs.; illus., incl. 2 tables
Summary:Fluids and melts have been trapped (in a diamond layer) and analysed by LA-ICP-MS in high-P experiments in the MgO-SiO2-H2O system at 6-10 GPa and 900-1200°C. Experiments on a serpentine starting composition result in MgO/SiO2 weight ratios in the subsolidus field close to 1 at 6 and close to 2 at 9 GPa. Melt compositions at 6 and 9 GPa have MgO/SiO2 ratios close to that of forsterite. At a single P, the amount of dissolved silicate in the fluid increase steadily with increasing T up to 1150°C, when a sudden increase of both MgO and SiO2 is observed. This discrete step marks the solidus, which is more clearly developed at 6 than at 9 GPa. Thus, hydrous melts within the model mantle subsystem Mg2SiO4-Mg2Si2O6-H2O are chemically distinct from aqueous fluids to ≥ 9 GPa, corresponding with 300 km depth. Extrapolation of the current data set implies that total convergence between fluid and melt along the solidus probably occurs at 12-13 GPa (∼ 400 km), i.e. close to the Earth's mantle transition zone. Beneath cratons, interactions of hydrous fluids with upper mantle lithologies cause relative silica depletion (olivine enrichment) at depths > 200 km and silica (orthopyroxene) enrichment at shallower depths. [R.A.H.]
Sections:Experimental mineralogy
Subsections:General
Subjects:Brucite; Chemical composition; Chemical ratios; Enrichment; Experimental studies; High pressure; High temperature; Magmas; Mantle; Melts; Mineral composition; Oxides; P-T conditions; Pressure; Temperature; Upper mantle
Abstract Numbers:01M/2801
Record ID:2001028795
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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