Phase relations in the system MgSiO3-FeSiO3 were studied experimentally up to a pressure of 24 GPa at 1800°C. Alumina-free tetragonal garnet exists in the pressure range from 16 to 23.5 GPa. The compositional range of the tetragonal garnet phase extends from pure MgSiO3 to (Mg0.76Fe0.24)SiO3 at 18.2 GPa and 1800°C. The sequence of the phase transitions in Mg-rich part of this system at 1800°C is: clinopyroxene → 17GPatetragonal garnet → 22.5GPailmenite → 23GPa Mg-perovskite. The lattice constants of tetragonal garnet increase with increasing iron content from a= 11.517 ± 0.002 A ̊ and c = 11.435 ± 0.003 A ̊ for MgSiO3 to a = 11.543 ± 0.002 A ̊ and c = 11.476 ± 0.003 A ̊ for (Mg0.76Fe0.24)SiO3. Cubic garnet was not observed in the pressure and temperature range studied in this work. The alumina-free tetragonal garnet observed in this study may exist in the harzbergite layer in the descending slab.
ASJC Scopus subject areas
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science