Significance Understanding the structural changes silicate melts undergo over the pressure–temperature range of the Earth’s mantle has been a major, longstanding challenge in the geosciences. Experimental studies are extremely difficult due to required temperatures exceeding 4,000 K needed to melt silicates over megabar pressures. To overcome this issue, laser-driven shock experiments combined with X-ray free-electron lasers were performed to provide nanosecond resolution on silicate structural transformations. By comparison with statically compressed diamond-anvil cell experiments at ambient temperature, a common high-pressure structural evolution of glasses and liquid silicates was revealed. This supports the concept that silicate glasses of dominant mantle composition are suitable structural analogues for the corresponding liquids at these pressures.