Thermodynamic formulations of (Ca, Fe, Mg)_2SiO_4 olivine

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Author(s)

    • KAWASAKI Toshisuke
    • Division of Earth Sciences, Department of Biosphere-Geosphere Sciences, Faculty of Science, Ehime University

Abstract

The multi-site regular solution model is applied to the intracrystalline exchange reaction of Fe<SUP>2+</SUP> and Mg<SUP>2+</SUP> between M1 and M2 sites of olivine. Effects of Ca on the Fe–Mg intracrystalline distribution coefficient <I>K<SUB>D</SUB></I>[=(<I>X</I><SUB>Mg</SUB><SUP>M2</SUP><I>X</I><SUB>Fe</SUB><SUP>M1</SUP>)⁄(<I>X</I><SUB>Fe</SUB><SUP>M2</SUP><I>X</I><SUB>Mg</SUB><SUP>M1</SUP>] are derived from this solution model, which indicates that Fe preferentially orders onto the lager M2 site accompanying with increasing Ca. This reaction would be assumed to be temperature-independent. The difference between Fe–Mg mixing parameters of M1 and M2 sites is very small and temperature-independent, so that the fayalite-forsterite olivine would be approximated as a binary regular solution.<BR>The miscibility gaps between high-Ca and low-Ca olivines are sufficiently described by the disordered multi-site regular solution model, which is very similar to a symmetric regular solution model. The present estimates for Margules parameters <I>W</I><SUB>MgCa</SUB><SUP>M2</SUP> is consistent with Davidson and Mukhopadhyay’s (1984) analysis of miscibility gap in Ca–Fe–Mg olivines, and is slightly less non-ideal than the Adams and Bishop’s (1985) results estimated from the mon-ticellite-forsterite solvus. The Ca–Fe mixing is more non-ideal than the previous estimates.

Journal

  • Mineralogical Journal

    Mineralogical Journal 20(3), 135-149, 1998-07-01

    Japan Association of Mineralogical Sciences

References:  46

Codes

  • NII Article ID (NAID)
    10008773224
  • NII NACSIS-CAT ID (NCID)
    AA00739590
  • Text Lang
    ENG
  • Article Type
    ART
  • ISSN
    05442540
  • Data Source
    CJP  J-STAGE 
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