First‐Principles Determination of the Dissociation Phase Boundary of Phase H MgSiO4H2. Issue 13 (8th July 2019)

• Record Type: Journal Article
• Authors: Tsuchiya, Jun; Umemoto, Koichiro
• Is Part Of: Geophysical research letters. Volume 46:Issue 13(2019)
• Page Start: 7333
• Page End: 7336
• Publication Date: 2019-07-08
• Subjects: hydrous mineral -- first principles -- free energy -- DHMS -- high pressure; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL083472
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Phase H (MgSiO4 H2 ) is considered an important carrier of water into the lower mantle by the subduction of slabs. This phase has been reported to decompose into H2 O ice VII and MgSiO3 bridgmanite under pressure. However, the dissociation phase boundary under the mantle pressure and temperature conditions has not been determined thus far. In this work, the dissociation phase boundary of phase H is determined by the calculation of Gibbs free energy of H2 O ice VII. The stability field of phase H is found to be significantly extended from 52 to 62 GPa by the inclusion of zero‐point vibrational energy. Phase H decomposes into MgSiO3 bridgmanite and H2 O ice VII at approximately 60 GPa (at ∼1000 K). This result indicates that the transportation of water by dense hydrous magnesium silicates may be terminated at a depth of approximately 1, 500 km in the middle of the lower mantle in a pure Mg‐endmember composition. Key Points: The dissociation phase boundary of phase H MgSiO4 H2 is determined by calculation of Gibbs free energy of ice VII Phase H decomposes into MgSiO3 bridgmanite and H2 O ice VII at approximately 60 GPa The transportation of water by DHMSs may be terminated at a depth of approximately 1, 500‐km depth in a pure Mg‐endmember composition