First‐Principles Determination of the Dissociation Phase Boundary of Phase H MgSiO 4 H 2
First‐Principles Determination of the Dissociation Phase Boundary of Phase H MgSiO 4 H 2
复制标题
H相MgSiO 4 H 2 解离相界的第一性原理测定
DOI：
10.1029/2019gl083472
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发表时间：
2019
影响因子：
5.2
通讯作者：
Umemoto Koichiro
中科院分区：
文献类型：
--
作者：
Tsuchiya Jun;Umemoto Koichiro
H相（MgSiO4H2）被认为是通过板块俯冲将水带入下地幔的重要载体。据报道，该相在压力下分解成 H2O 冰 VII 和 MgSiO3 桥石。然而，迄今为止，地幔压力和温度条件下的解离相边界尚未确定。在这项工作中，H相的解离相界是通过计算H2O冰VII的吉布斯自由能来确定的。通过包含零点振动能量，H 相的稳定场从 52 GPa 显着扩展至 62 GPa。 H 相在大约 60 GPa（约 1000 K）下分解成 MgSiO3 桥石和 H2O 冰 VII。这一结果表明，致密水合硅酸镁对水的输送可能终止于下地幔中部约 1,500 公里深度的纯镁端元成分中。
Phase H (MgSiO4H2) is considered an important carrier of water into the lower mantle by the subduction of slabs. This phase has been reported to decompose into H2O ice VII and MgSiO3bridgmanite 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 H2O 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 MgSiO3bridgmanite and H2O 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.