Post-garnet Transition in the System MgSiO₃-Al₂O₃

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Phase relations of the MgSiO₃-Al₂O₃ system were examined with special interest of post garnet transition. High pressure experiments were performed using 6-8 type multianvil apparatus based on conventional quenching method at pressures of 26 to 37 GPa and 1600 to 1800°C. It was observed that pyrope dissociates into perovskite solid solution plus corundum solid solution above about 26. 5 GPa, and it was suggested that this phase boundary has a very small negative slope. The stability field of single phase perovskite solid solution in the system MgSiO₃-Al₂O₃ extends as pressure increases, and perovskite solid solution isochemical with pyrope stabilizes at about 37 GPa and 1600°C.