Mattioli, Glen S. and Baker, Michael B. and Rutter, Michael J. and Stolper, Edward M.
Upper Mantle Oxygen Fugacity and Its Relationship to Metasomatism.
Journal of Geology, 97
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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.
|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 Sciences||4729|
|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.|
|Deposited On:||24 Aug 2012 18:24|
|Last Modified:||09 Dec 2016 20:31|
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