The Effect of Carbon Dioxide on Phase Relationships for Synthetic Lherzolite and Harzburgite'
نویسنده
چکیده
Wyllie , P. J . 1984 T he effect of carbon dioxide on phase relationships for synthetic lhe rzo lite and harzburgite. In : FL J. Zwart , P. Hartma n & A. C. Tobi (eds): Ophioli tes a nd ultramafic rocks a tribute to Emile den Tex Geol. Mijnbouw 63:213-2 19. T he system Ca0-Mg0-Si0 2 -C02 includes mineral assemblages corresponding to model lhe rzolite: fors te rite(Fo) + orthopyroxene(Opx) + clinopyroxene(Cpx) , a nd model harzburgite : Fo + Opx, as well as model webste ri te a nd wehrlite. Whe n fully carbonated, the pe ridotites are converted to limestones: dolomite(Do) + magnesite(Mc) + qua rtz(Qz), or Mc+ Qz. When partly carbona ted, the pe ridotites a re converted to carbonate-lherzoli te a nd magnesite-harzburgite , which cannot coexist with CO,. Available experimental and calculated reaction data are presented for carbona tc-lhe rzoli te: (6) Opx + Do=. Cpx + Fo + C02 and (6A) Opx + Cc = Cpx + Fo +CO,, where Do is dolomite and its solid so lution, and Cc is magnesium calcite; for magnesite-harzburgite: (3) MC+ En = Fo + C02; for webste ri te + carbonate: (0) Mc + Cpx = Do + Opx and (01) Do + Cpx = Cc + Opx; a nd for carbonate-wehrli te: (9)Do + Cpx = Fo + Cc + C02• Conditions for the occurre nce o f dolomite(stoichiome trjc)-lherzolite a re evaluated. Comparison of fossil geotherms deduced from kimbe rli te nodules with the phase diagrams fo r model harzburgite and lherzolite , and solidus curves with H20 present, indicates that pa rtially melted lhe rzolite may coexist with solid magnesiteharzburgite be tween about 175 and 195 km depth. D issociation of magnesite could disrupt the harzburgite nodules during e ruption, d istributing low-calcium garne t through ki mbe rlite. 213
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