Abstract
The convection or settling of matter in the deep Earth’s interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. is the main constituent of Earth’s mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of minerals above 60 GPa. The density data present two discontinuities at and that can be related to a silicon coordination increase from 4 to a mixed coordination and from to sixfold, respectively. glass becomes denser than glass at , and its density becomes identical to that of glass above 80 GPa. Our results on glass may suggest that a variation of content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle.
- Received 22 November 2016
DOI:https://doi.org/10.1103/PhysRevLett.119.215701
© 2017 American Physical Society