Research ArticleGEOLOGY

Transport properties of carbonated silicate melt at high pressure

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Science Advances  06 Dec 2017:
Vol. 3, no. 12, e1701840
DOI: 10.1126/sciadv.1701840

Figures

  • Fig. 1 Diffusion and viscosity coefficients of the carbonated MgSiO3 liquid at zero pressure.

    The calculated data points as a function of inverse temperature at 0 ± 1 GPa are shown by solid symbols. The straight lines are the Arrhenius representations. Also shown are the results for the pure liquid (open symbols) including the previous viscosity results (44) and experiment (21). The errors are shown for the selected results for the sake of clarity. prev calc, previous calculations; expt, experiments.

  • Fig. 2 Pressure variations of all ionic diffusivities of the carbonated MgSiO3 liquid at different temperatures.

    The solid symbols represent the calculated results for 16.1 wt % CO2 in the melt, and the solid line shows the Arrhenius trends (considering the data points at pressures above 10 GPa in most cases). The dashed line represents the Mg, Si, and O diffusivity results for the pure liquid (this study). The 3000 K results for the host elements are also shown (open symbols) for comparison with carbon diffusivity.

  • Fig. 3 Pressure variations of viscosity of the carbonated MgSiO3 liquid at different temperatures.

    The symbols show the calculated results for 16.1 wt % CO2 in the melt, and the straight lines represent the Arrhenius trends at pressures above 10 GPa. Also shown are the results for the pure liquid (open symbols) from this study and the previous calculations (26).

  • Fig. 4 Total (Mg, Si, and O) diffusivity and viscosity results for three CO2 concentrations of the MgSiO3 melt.

    The calculated results for 16.1 wt % CO2 (solid lines with circles) along with those for 5.2 and 30.5 wt % CO2 (diamonds and squares) are compared with the results of the pure and hydrous melts (with 10 wt % H2O) from the previous calculations (26, 36, 40). The inset shows the C diffusivity results for three different concentrations.

  • Fig. 5 Estimated electrical conductivity of the carbonated MgSiO3 melt.

    The results for the melt with 16.1 wt % CO2 (solid lines with circles) as a function of pressure at five temperatures (2200, 2500, 3000, 4000, and 5000 K) are compared with some results for 5.2 and 30.5 wt % CO2 concentrations (diamonds and squares) and the pure melt conductivity (dashed lines). Also shown are the calculated results of hydrous MgSiO3 melt (10 wt % H2O) at 0 GPa and different temperatures (asterisks). Previous computational values at 12 GPa and 2073 K (triangles) are for carbonated (20 wt % CO2) basaltic and kimberlitic melts (15). The experimental data (pluses) are for molten dry and hydrous basalt at 1873 K and 2 GPa (31) and hydrous carbonated basalt with hydrous contribution excluded (28) and carbonate peridotite at 1700 K and 3 GPa (32).

  • Fig. 6 Visualization snapshots of migrating carbon in the silicate melt.

    The net directions shown by the arrows are for carbon movements as CO2 molecule (upper left), CO3 carbonate (upper right and lower left), and then again as CO2 molecule (lower right) over 20 ps for a distance of about 7 Å. The simulated system corresponds to 0 GPa and 3000 K. The CO2 molecule shown as a big yellow sphere (carbon) connected with two small red spheres (oxygen) is present 30% of the time and almost always remains free (that is, only bound to Mg). The carbonate group shown as a big green sphere (carbon) and three small red spheres (oxygen) is present 70% of the time. It remains connected to the Si–O polyhedra 50% of the time, but it diffuses as a free unit 20% of the time. All other carbon species are shown as smaller purple spheres (carbon), each connected with either two or three red spheres (oxygen). The melt structure consists of Si–O tetrahedra (cyan) and pentahedra (blue) with an inhomogeneous distribution of Mg atoms (tiny green spheres). More structural details of carbonated silicate melt can be found in our recent publication (9).

Tables

  • Table 1 Arrhenius fit parameters for the temperature variations of different species diffusivities and viscosity at zero pressure (±1 GPa) of the carbonated MgSiO3 melt (with 16.1 wt % CO2).

    The model parameters for the pure melt (40, 44) are shown for comparison. Dα represents the self-diffusion coefficient for species α (Mg, Si, O, and C) and η represents the melt viscosity.

    DCDMgDSiDOη
    D0 (10−9 m2 s−1)η0 (10−5 Pa⋅s)
    Carbonated melt1223512105712553.5
    Pure melt47397313143.5
    ED (kJ/mol)Eη (kJ/mol)
    Carbonated melt128100149139125
    Pure melt105154151134