Calculated Mineral Reactions in the Earth's Mantle
نویسنده
چکیده
Thermochemical and compressibility data are used to calculate the approximate pressures and temperatures required for the reaction of clinoenstatite to Mg•SiO• (spinel or olivine) or to periclase and stishovite, the reaction of forsteritc to Mg•SiO• (spinel) or periclase and stishovite, and the breakdown of Mg•SiO• (spinel) to periclase and stishovite. The calculated reaction lines for Mg•SiO• (olivine) --• 2 MgO •SiO• and MgSi08 --• MgO •SiO• are p ---199 ñ 17 • 0.021T and p -182 ñ 17 • 0.024T (p in kilobars and T in degrees Celsius). These reaction lines lie at higher pressures than previously estimated. Because of the formation of Mg2SiO• (spinel) these two reactions probably do not take place in the earth's mantle. It appears, rather, that the reactions Mg•SiO• (olivine) --• Mg2SiO• (spinel), Mg_•SiO• (spinel) --• 2 MgO •SiOn, and 2 MgSi08 --• Mg•SiO• (spinel) •SiO• take place along p _-110 ñ 11 •0.024T, p -• 321 ñ 38 -0.013T, and p .• 133 ñ 19 -• 0.039 T, respectively.
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