Calorimetric study of the stability of high pressure phases in the systems CoOSiO2 and "FeO"SiO2, and calculation of phase diagrams in MOSiO2 systems

Alexandra Navrotsky, Faivel S. Pintchovski, Syun Iti Akimoto

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

High temperature calorimetric measurements of the enthalpies of solution in molten if2 PbO · B2O3 of α- and γ-Fe2SiO4 and α-, β-, and γ-Co2SiO4 permit the calculation of phase relations at high pressure and temperature. The reported triple point involving α-, β-, and γ-Co2SiO4 is confirmed to represent stable equilibrium. The curvature in the α-β phase boundary in Co2SiO4 and of an α-γ boundary in Fe2SiO4 at high temperature is explained in part by the effects of compressibility and thermal expansion, but better agreement with the observed phase diagram is obtained when one considers the effect of small amounts of cation disorder in the spinel and/or modified spinel phases. The calculated ΔH0 and ΔS0 values for the α-β, α-γ, and β-γ transitions show that enthalpy and en changes both vary strongly in the series Mg, Fe, Co, and Ni, and are of equal importance in determining the stability relations. The disproportionation of Fe2SiO4 and Co2SiO4 spinel to rocksalt plus stishovite is calculated to occur in the 170-190 kbar region; cation disorder and/or changes in wüstite stoichiometry can affect the P-T slope. The calorimetric data for CoSiO3 and FeSiO3 are in good agreement with the observed phase boundary for pyroxene formation from olivine and quartz. The decomposition of pyroxene to spinel and stishovite at pressures near the coesite-stishovite transition is predicted in both iron and cobalt systems. The use of calorimetric data, obtained from small samples of high pressure phases, is very useful in predicting equilibrium phase diagrams in the 50-300 kbar range.

Original languageEnglish (US)
Pages (from-to)275-292
Number of pages18
JournalPhysics of the Earth and Planetary Interiors
Volume19
Issue number4
DOIs
StatePublished - Aug 1979

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'Calorimetric study of the stability of high pressure phases in the systems CoOSiO<sub>2</sub> and "FeO"SiO<sub>2</sub>, and calculation of phase diagrams in MOSiO<sub>2</sub> systems'. Together they form a unique fingerprint.

Cite this