Melting of pyrope Mg3Al2Si3O12 up to 10 GPa: Possibility of a pressure‐induced structural change in pyrope melt

The melting of pyrope Mg3Al2Si3O12 has been determined experimentally at pressures up to 10 GPa. Pyrope melts congruently in the pressure range 3.5–10 GPa. At pressures below 7 GPa, aluminous enstatite of pyrope composition crystallizes during quenching, whereas quench pyrope appears at higher pressures. Moreover, the slope of the melting curve of pyrope decreases significantly at pressures above 7 GPa. These changes in both the nature of the quench phase and the slope of the melting curve suggest a pressure‐induced coordination change for Al3+ in pyrope melt at around 7 GPa. This pressure‐induced coordination change of Al3+ probably occurs even in magmatic liquids generated in the deep upper mantle and should affect some of their physical properties.