Synthesis and stability of Fe3 2+Fe2 3+Si3O12 garnet and phase relations with Fe3Al2Si3O12-Fe3 2+Fe2 3+Si3 O12 solutions

A. B. Woodland, H. S.C. O'Neill

Research output: Contribution to journalArticleResearchpeer-review

70 Citations (Scopus)

Abstract

Garnets containing both Fe2+ and Fe3+ are potentially useful monitors of fO2 in metamorphic rocks and garnet peridotites of the mantle. However, little is known about the properties or stability of such garnets. End-member Fe3 2+Fe2 3+Si3O12 garnet and garnet along the almandine (Fe3 2+Al2Si3O12)-Fe3 2+Fe2 3+Si3O12 join, where Al and Fe3+ mix on the octahedral sites were synthesized. At 1100°C, the equilibrium garnet solid solutions coexist with fayalite + spinel + quartz at P <1.6 GPa, with spinel + Fe2Si2O6 + quartz or coesite at 1.6 < P < 5.0 GPa, and with Si-rich spinel + coesite or stishovite above 5.0 GPa. The coexisting spinel and pyroxene are very Al poor, indicating that Al is strongly partitioned into the garnet. Based upon Al-Fe3+ exchange between garnet and spinel, a ΔfG1,1373 o = -2975.2 ± 3.0 kJ/mol is obtained for Fe3 2+Fe2 3+Si3O12. The spinel becomes increasingly Fe2SiO4-rich with increasing pressure. -from Authors

Original languageEnglish
Pages (from-to)1002-1015
Number of pages14
JournalAmerican Mineralogist
Volume78
Issue number9-10
Publication statusPublished - 1993
Externally publishedYes

Cite this