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Science 2 July 1993:
Vol. 261. no. 5117, pp. 66 - 68
DOI: 10.1126/science.261.5117.66
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Articles

Diamonds, Eclogites, and the Oxidation State of the Earth's Mantle

Robert W. Luth 1

1 C. M. Scarfe Laboratory of Experimental Petrology, Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

The reaction dolomite + 2 coesite rarrlarr diopside + 2 diamond + 2O2 defines the coexistence of diamond and carbonate in mantle eclogites. The oxygen fugacity of this reaction is sim1 log unit higher at a given temperature and pressure than the oxygen fugacities of the analogous reactions that govern the stability of diamond in peridotite. This difference allows diamond-bearing eclogite to coexist with peridotite containing carbonate or carbonate + diamond. This potential coexistence of diamond-bearing eclogite and carbonate-bearing peridotite can explain the presence of carbon-free peridotite interlayered with garnet pyroxenites that contain graphitized diamond in the Moroccan Beni Bousera massif at the Earth's surface and the preferential preservation of diamond-bearing eclogitic relative to peridotitic xenoliths in the Roberts Victor kimberlite.

Submitted on January 14, 1993
Accepted on April 20, 1993


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Science. ISSN 0036-8075 (print), 1095-9203 (online)