Effect of clinopyroxene composition on Fe-Mg distribution coefficient between garnet and clinopyroxene

Daisuke Nakamura, Madoka Okada, Takao Hirajima

Research output: Contribution to journalLetter

2 Citations (Scopus)

Abstract

This study examines the effect of jadeite content (Xjd) in omphacite on Fe-Mg distribution coefficient between garnet and clinopyroxene (KD) by using natural data obtained from ultrahigh-pressure eclogites of the Sulu region, China. A previous study has already pointed out that a negative correlation between lnKD and Xjd and a positive correlation between Fe# [= Fe2+/(Fe2+ + Mg)] of omphacite and Xjd are present. On the other hand, this study newly recognized that KD decreases with decreasing Ca + Na + K contents in M2 site of omphacite, indicating that excess Fe2+ may be incorporated into M2 site of omphacite with decreasing Ca + Na + K contents and hence total Fe# values of omphacite may become excessively high. Thus, application of garnet-clinopyroxene geothermometer for omphacite with significant amount of jadeite and/or ferrosilite (and enstatite) components may overestimate the peak metamorphic temperatures in some cases. As a first approximation, it is better to avoid the use of omphacite with Ca + Na + K contents significantly lower than 1.0 a.p.f.u. for the application of garnet-clinopyroxene geothermometer.

Original languageEnglish
Pages (from-to)82-87
Number of pages6
JournalJournal of Mineralogical and Petrological Sciences
Volume110
Issue number2
DOIs
Publication statusPublished - Jan 1 2015

Keywords

  • Clinopyroxene
  • Fe-Mg distribution coefficient
  • Garnet
  • Geothermometer
  • Jadeite

ASJC Scopus subject areas

  • Geophysics
  • Geology

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