Abstract

The pressure–temperature stability field of pyrope was experimentally determined in reversed equilibrium experiments up to 10 GPa within the system MgO–Al2O3–SiO2–H2O. The lower pressure limit of pyrope is defined by reactions to aluminous enstatite + sapphirine + kyanite (1.5 GPa, 950–1050 °C) and to aluminous enstatite + corundum (1.5–1.7 GPa, 800–950 °C). Between 1.7 and 1.8 GPa pyrope is formed from the assemblage enstatite + chlorite + Mg-staurolite. The curve talc + Mg-staurolite + kyanite = pyrope + H2O marks the pyrope in field between 1.8 and 1.9 GPa, and at higher pressures up to 4 GPa pyrope forms from chlorite + talc + kyanite. Beyond 4 GPa, the assemblage talc + chlorite + Mg-chloritoid defines the lower temperature limit around 600 °C. At pressures higher than 5 GPa, pyrope forms via the reactions low-clinoenstatite + chlorite + Mg-sursassite = pyrope + H2O and high-clinoenstatite + forsterite + Mg-sursassite = pyrope + H2O (with increasing pressure). The bracketing results indicate that all these reactions have a high positive dP/dT-slope. Pyrope is a high-pressure phase stable only at mantle depths.

You do not currently have access to this article.