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The effect of carbon dioxide on phase relationships for synthetic lherzolite and harzburgite

Wyllie, Peter J. (1984) The effect of carbon dioxide on phase relationships for synthetic lherzolite and harzburgite. Geologie en mijnbouw, 63 . pp. 213-219. ISSN 0016-7746.

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The system CaO-MgO-SiO_2-CO_2 includes mineral assemblages corresponding to model lherzolite: forsterite(Fo) + orthopyroxene(Opx) + clinopyroxene(Cpx), and model harzburgite: Fo + Opx, as well as model websterite and wehrlite. When fully carbonated, the peridotites are converted to limestones: dolomite(Do) + magnesite(Mc) + quartz(Qz), or Mc + Qz. When partly carbonated, the peridotites are converted to carbonate-lherzolite and magnesite-harzburgite, which cannot coexist with CO_2. Available experimental and calculated reaction data are presented for carbonatc-lherzolite: (6) Opx + Do = Cpx + Fo + CO_2 and (6A) Opx + Cc = Cpx + Fo + CO_2, where Do is dolomite and its solid solution, and Cc is magnesium calcite; for magnesite-harzburgite: (3) MC+ En = Fo + CO_2; for websterite + carbonate: (0) Mc + Cpx = Do + Opx and (01) Do + Cpx = Cc + Opx; and for carbonate-wehrlite: (9)Do + Cpx = Fo + Cc + CO_2. Conditions for the occurrence of dolomite(stoichiome trjc)-lherzolite are evaluated. Comparison of fossil geotherms deduced from kimbe rlite nodules with the phase diagrams for model harzburgite and lherzolite, and solidus curves with H_2O present, indicates that partially melted lherzolite may coexist with solid magnesiteharzburgite between about 175 and 195 km depth. Dissociation of magnesite could disrupt the harzburgite nodules during eruption, distributing low-calcium garnet through kimberlite.

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Additional Information:© 1984 Geologie en Mijnbouw. Manuscript received: 1983-09-30; Manuscript accepted: 1984-05-01. This research was supported by the Earth Sciences Section of the National Science Foundation, EAR-8311758. I thank W.-L. Huang, A. P. Byrnes, and J. Otto for their contributions to this research program, through years at the University of Chicago, and R. C. Newton for consultations, and E. Woermann for discussions.
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ID Code:65561
Deposited By: Tony Diaz
Deposited On:24 Mar 2016 23:46
Last Modified:03 Oct 2019 09:48

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