High-pressure and high-temperature stability of chlorite and 23-Å phase in the natural chlorite and synthetic MASH system

Abstract

Listen

Translate article

A series of experiments was conducted on the decomposition of natural and chemically mixed chlorites to examine the stable hydrous phases in the MgO–FeO–Al2O3–SiO2–H2O (MFASH) system under 5–12GPa and 700–1100°C. The upper pressure and temperature limits of the stability region of chlorite are consistent with those observed in previous studies. The hydrous aluminum bearing pyroxene (phase HAPY) and Mg-sursassite (Sur) were observed just above the temperature stability region of chlorite (Chl); clinohumite (cHm) was observed coexisting with phase HAPY at 6GPa and 800°C and coexisting with the 23-Å phase at 7GPa and 800°C, which may suggest the transportation of water through Chl→(HAPY→cHm)→23-Å phase along a relatively warm slab. The 23-Å phase has a wider stability region in the pure MASH system (up to 12GPa and 1100°C) than it does in the MFASH system (7–10GPa, up to 1000°C). The stability of the 23-Å phase beyond the chlorite breakdown pressure indicates that it may play an important role in transporting water into the deep Earth and even into the mantle transition zone.