Structural dynamics of basaltic melt at mantle conditions with implications for magma oceans and superplumes

Abstract

Transport properties like diffusivity and viscosity of melts dictated the evolution of the Earth’s early magma oceans. We report the structure, density, diffusivity, electrical conductivity and viscosity of a model basaltic (Ca11Mg7Al8Si22O74) melt from first-principles molecular dynamics calculations at temperatures of 2200 K (0 to 82 GPa) and 3000 K (40–70 GPa). A key finding is that, although the density and coordination numbers around Si and Al increase with pressure, the Si–O and Al–O bonds become more ionic and weaker. The temporal atomic interactions at high pressure are fluxional and fragile, making the atoms more mobile and reversing the trend in transport properties at pressures near 50 GPa. The reversed melt viscosity under lower mantle conditions allows new constraints on the timescales of the early Earth’s magma oceans and also provides the first tantalizing explanation for the horizontal deflections of superplumes at ~1000 km below the Earth’s surface.

Six ‘Must-Have’ Minerals for Life’s Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite

“…The four essential minerals in planetary bodies needed to produce the chemical disequilibria and materials required for life’s emergence are olivine ([Mg>Fe] 2 SiO 4 ), bridgmanite ([Mg,Fe]SiO 3 ), serpentine ([Mg,Fe,] 2-3 Si 2 O 5 [OH)] 4 ) and pyrrhotite (Fe (1-x) S). We begin with olivine, a ubiquitous mineral contributing to the primary extrusive and intrusive basaltic or komatiitic ocean floor, crust and upper mantle (originally as short-lived magma oceans [ 70 ]) to a myriad of putative planets—the precursor to suites of minerals produced through the stressors of pressure, thermal gradients and hydration. We proceed with the most abundant of these—bridgmanite (Mg,Fe)SiO 3 )—which is hidden at depth out of reach of spectroscopy.…”

“…In the Hadean (4.5 to 4.0 billion years before present (Ga)), in what is now the Earth’s mantle, olivine began to precipitate in a relatively short-lived magma ocean and in super plumes induced through giant impacts [ 8 , 70 , 84 , 85 ]. A depth of 410 km marks the beginning of a transition zone in the mantle.…”

Electronic, Structural, and Mechanical Properties of SiO2 Glass at High Pressure Inferred from its Refractive Index

“…Among the relevant physical properties of melts, their density and viscosity are of primary geophysical importance because they determine the ability of magmas to rise or sink. These two properties are linked to the compressibility and structure of silica-rich melts [9], which remain largely inaccessible to direct probing at deep mantle conditions [10,11]. Silica-bearing liquids, however, present structural similarities to corresponding glasses [12,13], rendering the latter convenient and appropriate proxies of the molten state.…”

Computer simulation of the glassy network structure of B2O3-2SiO2 and Al2O3-2SiO2 systems

“…Therefore, borosilicate glass is applied in storage medium for nuclear waste. Using 2 principles MD calculations investigate structure of basaltic [19] at 2200K and 3000K, pressure up to 82 GPa, authors found that the coordination numbers around Si and Al atom increase with pressure. The Si-O and Al-O bonds become more ionic and weaker.…”

“…Hence, simulation method is still an effective tool to elucidate these problems. The computer simulations for silicates systems have been intensively studied at conditions of different temperatures and pressures [12,19,[25][26][27][28][29][30][31]. The results showed that the chemical order in silicate materials is very complicated.…”