Notes on Rock-forming Minerals(26)Enstatite from a Garnet-Peridotite Inclusion in Kimberlite

昇平, 坂野; 育夫, 久城; 義人, 松井

doi:10.5575/geosoc.69.157

Cited by 5 publications

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“…The relative abundances of the components are, however, different between garnetfree and garnet-bearing peridotires. For example, the content of alumina or Mg-Tsehermak's component is smaller in orthopyroxene from garnet-peridotite inclusion in kimberlite than in orthopyroxene from garnet-free peridotitc inclusions in basalts, as sho,wn by Banno et al [1963] and O'Hara and Mercy [1963]. Green and Ringwood [1967] suggested that garnetfree peridotitc is stable down to at least 100 km (~30 kb) and garnet peridotitc is stable below 100-120 km at near-solidus temperatures for 'pyrolite' composition.…”

Section: Introductionmentioning

confidence: 96%

Compositions of magmas formed by partial zone melting of the Earth's upper mantle

Kushiro¹

1968

J. Geophys. Res.

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219

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The upper mantle of the earth is probably composed of peridotites consisting mainly of olivine, orthopyroxene, clinopyroxene, and garnet or spinel similar to those found as inclusions in kimberlite and basaltic rocks. The compositions of the magmas produced by the partial melting of the mantle peridotites are closely dependent on the position of the isobaric invariant point where olivine and orthopyroxene are involved in systems including components of minerals of the mantle peridotites. The positions of such invariant points have been investigated in the systems Mg•SiO•-SiO2-X, where X represents CaMgSiO•, CaA120•, NaA1SiO•, and MgA120•, in the pressure range 7 to 40 kb. It was found that the liquidus boundary between forsteritc and enstatite solid solution and the invariant point where forsteritc and enstatite solid solution are involved shift from silica-rich compositions toward silica-poor compositions with increasing pressure up to at least 40 kb in all the systems examined. The experimental results suggest that the compositions of the magmas produced by the partial melting of the mantle peridotires would become more silica-deficient with increasing pressure. It is also suggested that magmas consisting essentially of pyroxene and garnet components are formed by partial melting of the mantle peridotites at pressures less than 30 kb. Magmas formed in the upper mantle by partial melting would ascend by the mechanism of 'partial zone melting' in the levels where temperature is close to the beginning of melting of the mantle peridotires. Compositional change in the magmas that ascend by the partial zone melting is dependent on the isobaric invariant point where olivine and orthopyroxene are involved and can be estimated on the basis of the present experiments.

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Section: Introductionmentioning

confidence: 96%