Density and Transport Properties of Silicate Melts

Silicate melts constitute the liquid phase of Earth’s mantle and crustal magmas, underpinning processes from magma ocean crystallisation to modern volcanism. Their density and transport properties—encompassing viscosity, diffusivity, sound velocity and electrical conductivity—are governed by pressure, temperature, chemical composition and volatile content. Under increasing pressure, coordination environments of network-forming cations evolve, driving densification and modifying melt buoyancy. Temperature exerts a competing effect, lowering viscosity and enhancing atomic mobility. The presence of water and other volatiles alters melt structure, reducing viscosity and density, and influencing electrical conduction through fast hydrogen transport. Experimental techniques such as in situ ultrasonic measurements, X-ray microtomography and falling-sphere viscometry complement first-principles molecular dynamics to map the equation of state and dynamic behaviour across a broad pressure–temperature regime. These insights inform geodynamic models of melt segregation, ponding at mantle boundaries, deep carbon and water cycles, and magma-driven convective overturns in the early Earth.

Research from Nature Portfolio

Recent first-principles simulations of basaltic compositions under lower-mantle pressures reveal that Fe and Si coordination numbers increase sharply above 6 GPa, accounting for a viscosity minimum followed by steady hardening with compression. Elevated magma-ocean temperatures constrain viscosity to a narrow range (0.01–0.03 Pa·s), implying rapid fractional crystallisation within a few million years. Atomistic studies of hydrous Mg–Fe silicate melts demonstrate that water lowers density mainly at low pressures, with volume effects nearly null above 15 GPa. Hydrogen diffuses rapidly, enhancing melt electrical conductivity and producing extended hydroxyl and polyhydroxyl species under deep-mantle conditions. Combined, these works refine our understanding of how volatile-bearing melts evolve in deep reservoirs and influence the timing and style of mantle differentiation.

Density and Transport Properties of Silicate Melts publication trend

The graph below shows the total number of articles in density and transport properties of silicate melts across all publications each year (not limited to Nature Index journals).

Technical terms

Silicate melt: A high‐temperature liquid dominated by silica and metal oxides, forming the fluid phase of magmas.

Viscosity: A measure of a fluid’s resistance to flow, reflecting internal friction between its particles.

Density: Mass per unit volume of a melt, determining its buoyancy relative to surrounding solid mantle.

Diffusivity: Rate at which atoms or molecules move through a melt, governing chemical homogenisation and electrical conduction.

Buoyancy: Net upward force on a melt parcel driven by density contrasts with its environment.

First‐principles molecular dynamics: Computational simulation method based on quantum mechanics, used to predict atomic structure and properties without empirical parameters.

References

1. Structure and density of basaltic melts at mantle conditions from first-principles simulations. Nature Communications (2015).
2. Insights into magma ocean dynamics from the transport properties of basaltic melt. Nature Communications (2022).
3. Hydrous silicate melts and the deep mantle H2O cycle. Earth and Planetary Science Letters (2022).
4. Structure and Density of H2O‐Rich Mg2SiO4 Melts at High Pressure From Ab Initio Simulations. Journal of Geophysical Research: Solid Earth (2020).
5. Density of NaAlSi2O6 Melt at High Pressure and Temperature Measured by In-Situ X-ray Microtomography. Minerals (2020).
6. High-Pressure Sound Velocity Measurements of Liquids Using In Situ Ultrasonic Techniques in a Multianvil Apparatus. Minerals (2020).