Sodium Silicates at the Boundary between the Transition Zone and the Lower Mantleстатья
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Дата последнего поиска статьи во внешних источниках: 27 мая 2020 г.
Аннотация:The new results of experimental study of the Na2MgSiO4–Mg2SiO4 section of the SiO2–MgO–Na2O model system at 22–24 GPa and 1600–1900C are discussed in this paper. An association of Na-bearing ringwoodite (up to 0.42 wt % Na2O) and the phase with the composition Na2MgSiO4 with a cristobalitetype structure was obtained at 22 GPa. Incorporation of Na in ringwoodite occurs through the mechanism Mg2+ 2/3Na+ + 1/3Si4+ and results in an increase in the cell parameter in relation to that of pure Mg2SiO4 ringwoodite. A paragenesis of Na-bearing bridgmanite (up to 0.67 wt % Na2O), periclase, and anhydrous sodium phase X (Na2Mg2Si2O7) is formed at 23–24 GPa. Based on the data obtained, high-pressure Na–Mg silicates, Na2MgSiO4 and Na2Mg2Si2O7, may be considered as mineralogically probable mantle phases within the locally metasomatized mantle regions, although their finds as inclusions in diamond crystals are unlikely.