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Upper Mantle Oxygen Fugacity and Its Relationship to Metasomatism

Mattioli, Glen S. and Baker, Michael B. and Rutter, Michael J. and Stolper, Edward M. (1989) Upper Mantle Oxygen Fugacity and Its Relationship to Metasomatism. Journal of Geology, 97 (5). pp. 521-536. ISSN 0022-1376. doi:10.1086/629332.

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We have calculated fO_2's and temperatures of various mantle environments worldwide using published analyses of coexisting olivine, orthopyroxene, clinopyroxene, and Fe^(3+)-bearing spinel from 280 peridotites. Most calculated fO_2's fall within ± 2 log units of the Fayalite-Magnetite-Quartz (FMQ) buffer at 15 kbar. Our data set defines a general trend in fO_2-T space that is not related to FMQ or to other Fe-bearing buffers. Variations in major-element, trace-element, and oxygen isotopic composition of xenoliths correlate with variations in calculated fO_2. Rare "fertile" xenoliths record fO_2's close to WM (Wüstite-Magnetite) buffer at 15 kbar and 900°C. Xenoliths with both cryptic and/or modal metasomatic overprinting are generally oxidized relative to xenoliths without evidence of such open system processing. Based on trace element and oxygen isotopic data, the best candidate for the metasomatic agent is a CO_2-H_2O-rich fluid. We suggest that metasomatic fluids are derived from oxidized, hydrated material subducted at convergent margins and that this process may have led to progressive oxidation of the earth's upper mantle through much of geologic time. This is consistent with the observation that xenoliths from Hawaii and Tahiti record fO_2's higher than mantle array's average, as do some xenoliths from the circumpacific region.

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Stolper, Edward M.0000-0001-8008-8804
Additional Information:© 1989 University of Chicago. Manuscript received December 19, 1988; accepted April 25, 1989. G. Mattioli was supported at Caltech as a Dr. Chaim Weizmann Fellow in the Division of Geological and Planetary Sciences during this project. M. Baker and M. Rutter were supported by the NSF by a grant to Prof. P. J. Wyllie (EAR-87-19792). Prof. E. Stolper was supported in part by grants from the NSF (EAR-87-18229) and from NASA (NAG9-105). Division of Geological and Planetary Sciences contribution number 4729. We thank J.D. Pasteris for her review.
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Caltech Division of Geological and Planetary Sciences4729
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Official Citation:Upper Mantle Oxygen Fugacity and Its Relationship to Metasomatism Glen S. Mattioli, Michael B. Baker, Michael J. Rutter and Edward M. Stolper The Journal of Geology Vol. 97, No. 5 (Sep., 1989), pp. 521-536
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33508
Deposited On:24 Aug 2012 18:24
Last Modified:09 Nov 2021 21:35

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