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Knowledge of the pressure–density relations and elastic properties of silicate melts at high pressure and temperature conditions is fundamental for a better understanding of the dynamics and properties of the Earth's interior. Here we report the sound velocities and elastic properties of vitreous MgSiO₃-enstatite, a simple analog for melts in the Earth's mantle, determined up to 33.4±1.2GPa in a diamond anvil cell by Brillouin scattering spectroscopy. The adiabatic bulk and shear moduli of MgSiO₃ glass at ambient conditions are K_S0=78.4(6) GPa and µ₀=41.1(3) GPa, corresponding to compressional and shear wave velocities of V_P=6.969(30) km/s and V_S=3.868(20) km/s. On compression both longitudinal V_P and transverse V_S modes exhibit anomalous change in slope at 8GPa and between 15.0(1) and 17.9(2) GPa, that are associated with polyamorphic phase transitions in the glass. The acoustic data were used …