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Published June 1978 | Published
Journal Article Open

The effect of H_2O and CO_2 on planetary mantles

Abstract

The solidus for peridotite-H_2O-CO_2 is a divariant surface traversed by univariant lines that locate the intersections of subsolidus divariant surfaces for carbonation or hydration reactions occurring in the presence of H_2O-CO_2 mixtures. Vapor phase compositions are normally buffered to these lines; the buffering capacity of carbonates is much greater than that of amphibole and phlogopite. Near the buffered curve for the solidus of partly carbonated peridotite, extending to higher pressures and lower temperatures from an invariant point near 26 kb-1200°C, there is a temperature maximum on the peridotite-vapor solidus. On the CO_2 side of the maximum, above 26 kb, CO_2/H_2O is greater in liquid than in vapor, and liquids are SiO_2-poor; on the H_2O side of this maximum (including all pressures below 26 kb), H_2O/CO_2 is greater in liquid than in vapor, and liquids change from forsterite-normative to quartz-normative with increasing H_2O/CO_2 in vapor. Even traces of H_2O and CO_2, in minerals or vapor, lower mantle solidus temperatures through hundreds of degrees compared with the volatile-free solidus.

Additional Information

Copyright 1978 by the American Geophysical Union. (Received February 17, 1978; revised April 4, 1978; accepted April 20, 1978.) Paper number 8L0487. This research was supported by the Earth Sciences Section, National Science Foundation, NSF Grant EAR 76-20410. Supported in part by the Materials Research Laboratory Program of the National Science Foundation at the University of Chicago. This paper constitutes Contribution No. 25 of the Basaltic Volcanism Study Project, which is organized and administered by the Lunar and Planetary Institute/Universities Space Research Association under Contract NSR 09-051-001 with the National Aeronautics and Space Administration.

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Created:
August 22, 2023
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October 18, 2023