Equation of state of silicate melts with densified intermediate-range order at the pressure condition of the Earth’s deep upper mantle
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The knowledge from the compression behavior of densified SiO2 glass suggests that SiO2 melt may behave as a single phase having a densified network structure (intermediate-range order) at the pressure condition of the Earth’s deep upper mantle, including the transition zone. A simple and easy-to-use equation of state of silicate melts which is applicable to a wide range of chemical composition at the pressure condition of the deep upper mantle is proposed based on the assumption that SiO2 component is in its densified state (or phase). The equation of state proposed in this study is consistent with all the available density data of silicate melts with an SiO2 content of about 35–55 mol% measured with large-volume presses at pressures between 8 and 22 GPa. The equations of state in previous studies differ considerably from each other. The main reason for the discrepancies seems to be that the compression behavior of multiple states (or phases) of silicate melts has been described in most cases with a single equation of state. It is necessary to consider that silicate melts are in their densified states (or phases) in the deep upper mantle.
KeywordsSilicate melt Equation of state Deep upper mantle Densified network structure Silica glass Permanent densification
The authors are grateful for critical and constructive comments by three anonymous reviewers. One of the authors (D.W.) is supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. This work was in part supported by Grant-in-Aid for Scientific Research (Japan).
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