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Thermodynamics of the MgO‐FeO‐SiO 2 system up to 140 GPa: Application to the crystallization of Earth's magma ocean
Author(s) -
Boukaré C.E.,
Ricard Y.,
Fiquet G.
Publication year - 2015
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2015jb011929
Subject(s) - mantle (geology) , crystallization , geology , planetary differentiation , core–mantle boundary , thermodynamics , olivine , early earth , fractional crystallization (geology) , structure of the earth , geophysics , mineralogy , geochemistry , mantle convection , lithosphere , physics , tectonics , paleontology
At the end of Earth's accretion and after the core‐mantle segregation, the existence of a basal magma ocean at the top of the core‐mantle boundary (CMB) depends on the physical properties of mantle materials at relevant pressure and temperature. Present‐day deep mantle structures such as ultralow‐velocity zones and low‐shear velocity provinces might be directly linked to the still ongoing crystallization of a primordial magma ocean. We provide the first steps toward a self‐consistent thermodynamic model of magma ocean crystallization at high pressure. We build a solid‐liquid thermodynamic database for silicates in the MgO‐FeO‐SiO 2 system from 20 GPa to 140 GPa. We use already published chemical potentials for solids, liquid MgO, and SiO 2 . We derive standard state chemical potential for liquid FeO and mixing relations from various indirect observations. Using this database, we compute the ternary phase diagram in the MgO‐FeO‐SiO 2 system as a function of temperature and pressure. We confirm that the melt is lighter than the solid of same composition for all mantle conditions but at thermodynamic equilibrium, the iron‐rich liquid is denser than the solid in the deep mantle. We compute a whole fractional crystallization sequence of the mantle and show that an iron‐rich and fusible layer should be left above the CMB at the end of the crystallization.