The alpha , beta , gamma phase relations in Fe2SiO4- Mg2SiO4 and Co2SiO4-Mg2SiO4: calculation from thermochemical data and geophysical applications.

A. Navrotsky, M. Akaogi

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32 Scopus citations

Abstract

On the basis of thermochemical data for olivine (alpha ), modified spinel (beta ), and spinel (gamma ) polymorphs of Mg2SiO4, Fe2SiO4 and Co2SiO4, the binary Mg2SiO4-Fe2SiO4 and Mg2SiO4-Co2SiO4 phase diagrams are calculated. From Mg/Fe partitioning data between olivine-garnet, beta -phase-garnet, olivine-pyroxene and beta -phase-pyroxene, thermochemical parameters for beta -Fe2SiO4 are estimated. The beta -Fe2SiO4 is highly metastable with respect to gamma -Fe2SiO4. The calculated binary Mg2SiO4-Fe2SiO4 phase diagram shows a narrow field of alpha + beta and a broad field of beta + gamma in reasonable agreement with experimental phase relations. The composition range over which beta -phase solid solution is stable expands with increasing temperature but is generally limited to Mg/(Mg + Fe) >0.8. In the Mg2SiO4-Co2SiO4 system, the beta -phase is calculated to occur only at Mg/(Mg + Co) <0.05 and Mg/(Mg + Co) >0.6 with alpha and gamma coexisting at intermediate compositions. Using the phase relations in Mg2SiO4-Fe2SiO4 and assuming an adiabatic geotherm, temperatures are calculated to range from approx 1573 to 1700 K at depths of 400-520 km for a mantle of lherzolite composition.-W.H.B.

Original languageEnglish (US)
Pages (from-to)10135-10140
Number of pages6
JournalJournal of geophysical research
Volume89
Issue numberB12
DOIs
StatePublished - 1984

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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