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We determined the melting phase relations and conditions of the dense hydrous magnesium silicate phase D (nominally MgSi₂O₄(OH)₂) on composition in MgO–SiO₂–H₂O (MSH), MgO–Al₂O₃–SiO₂–H₂O (MASH), and FeO–MgO–Al₂O₃–SiO₂–H₂O (FMASH), and on a mixture of phase D + olivine + enstatite (MSH) at 22–32 GPa and 1000–1800 °C. Contrasting to previous studies, we performed H₂O-undersaturated experiments. Bulk compositions were synthetic mixtures of brucite + silica or brucite + olivine + enstatite on the silica-rich side of the tie-line perovskite–H₂O. At 22–24 GPa, the maximum thermal stability of phase D is between 1350 and 1400 °C in MSH and FMASH, but 1600 °C at 24 GPa in the Fe-free, Al-bearing bulk composition (MASH). Apparently, addition of Al₂O₃ increases the stability field of phase D by 200 °C, an effect that is counter balanced by addition of FeO. At 32 GPa, the stability of …