Upper mantle oxidation state; ferric iron contents of lherzolite spinels by 57Fe Mössbauer spectroscopy and resultant oxidation fugacities

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doi: 10.1016/0016-7037(89)90062-8
Authors:Wood, Bernard J.; Virgo, David
Author Affiliations:Primary:
Northwest. Univ., Dep. Geol. Sci., United States
Geophys. Lab., United States
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 53(6), p.1277-1291. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1989
Note:In English. 51 refs.; illus. incl. 4 tables
Summary:In order to improve the estimation of mantle O fugacity by the thermobarometric method, accurate analytical data for the Fe3O4 contents of spinel phases are presented through the determination of Fe3+ contents of spinels from 30 spinel lherzolite xenoliths, using microprobe and Mossbauer spectroscopy. Comparison of Mossbauer analyses with Fe3+ contents derived from recalculation of microprobe analyses shows large systematic errors in the latter method, though the precision of microprobe analyses is sufficiently good provided well-analysed standards (by Mossbauer spectroscopy) are used. Fe3O4 contents of the spinels analysed range 1.7-5.2 mol%, with an uncertainty of 0.2-0.3 mol%; these results were used to calculate recorded by the spinel lherzolites. The Fe3+ results translate to at 15 kbar, from 1.7 log units below and 1.2 log units above the fayalite-magnetite-quartz (FMQ) buffer. Regional differences in the derived values are discussed and overlap the - T field of MORB glasses, indicating that many of the samples relate to MORB sources. The results are > 2 log units above Fe-wustite, indicating that C-H-O fluids in the upper mantle are dominated by CO2 and H2O, and that CH4 is minor. [R.K.H.]
Subjects:Fugacity; Geochemistry; Igneous rocks; Inclusions; Iron; Mantle; Metals; Mineral composition; Mossbauer spectra; Oxidation; Oxides; P-T conditions; Peridotites; Plutonic rocks; Processes; Spectra; Spinel; Spinel lherzolite; Ultramafics; Upper mantle; Xenoliths
Abstract Numbers:90M/2038
Record ID:1989051915
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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