Petedunnite (CaZnSi2O6): Stability and phase relations in the system CaO-ZnO-SiO2

Alexandra L. Huber*, Soraya Heuss-Assbichler, Karl Thomas Fehr, Geoffrey D. Bromiley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The phase relations of petedunnite [CaZnSi2O6 (pd)] were determined experimentally at P-T conditions up to 2.5 GPa and 1100 degrees C. Single-phase petedunnite is formed at high pressures (P > 0.8 GPa). Reversed experiments show that at lower pressures and temperatures >650 degrees C petedunnite decomposes to willemite [Zn2SiO4 (wil)], hardystonite [Ca2ZnSi2O7 (har)], and quartz [SiO2 (qtz)] according to the reaction 4 pd = wil + 2 har + 3 qtz. The boundary curve for this equilibrium reaction is given by P (GPa) = -0.093 (0.029) + 0.0014 (0.0003) T (degrees C), by disregarding the phase transition of quartz. The stability field of wil + bar + qtz is restricted toward lower temperatures by zinc-feldspar [CaZn-SiO8 (zfsp)] according to the known reaction: wil + 2 har + 7 qtz = 4 zfsp. These reactions intersect at 650(1) degrees C/0.78(0.01) GPa, generating an invariant point I-pd. Additionally, petedunnite-breakdown reaction is intersected by the low/high-quartz phase transition curve, generating an invariant point I-qtz(pd) at similar to 840 degrees C, 1.04 GPa. At temperatures

The study of natural clinopyroxene and the correlation of its zinc content with published P-T conditions of these mineral assemblages confirmed a significant relationship between extraordinary high-zinc concentrations in pyroxene and high-metamorphic pressure conditions. In addition, the petedunnite component is obviously sensitive to the prevailing fluid conditions in terms of the fugacity ratio fs(2)/fo(2.) Furthermore, a distinct temperature dependency of the zinc component was observed in the range of trace element concentration. In consequence, Zn turns out to be a key element with regard to its implementation as a sophisticated petrogenetic indicator of metamorphic conditions. Therefore, routine measurement of zinc in element analyses of clinopyroxenes is strongly recommended.

Original languageEnglish
Pages (from-to)739-749
Number of pages11
JournalAmerican Mineralogist
Volume97
Issue number4
DOIs
Publication statusPublished - Apr 2012

Keywords

  • Zinc
  • clinopyroxene
  • petedunnite
  • stability
  • phase relations
  • skarn
  • petrogenetic indicator
  • geobarometry
  • experimental calibration
  • ZINC CATENA-DISILICATE
  • SOLID-SOLUTION SERIES
  • NEW-JERSEY HIGHLANDS
  • MINERAL ASSEMBLAGES
  • CRYSTAL-STRUCTURE
  • SULFUR ISOTOPE
  • SKARN DEPOSITS
  • CENTRAL SWEDEN
  • LOW-PRESSURE
  • BERGSLAGEN

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