Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle
Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle
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DOI：
10.3390/min10040330
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发表时间：
2020-04
期刊：
影响因子：
2.5
通讯作者：
W. R. Panero;R. Caracas
中科院分区：
文献类型：
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作者：
W. R. Panero;R. Caracas
地幔储存和循环水的程度超过名义上无水矿物的储存能力，取决于在地幔相关压力、温度和成分下含水相的稳定性。D相和H相两个含水相对地球下地幔的压力和温度是稳定的，这表明地球下地幔可能参与了水的循环。我们建立在我们以前的工作的密度泛函理论计算相H的稳定性，结构，和键的水合相D，我们预测铝分配与H在Al 2 O3-SiO2-MgO-H2O系统。我们解决的固溶体通过统计抽样的网站占有率和计算的配分函数从巨正则系综。结果表明，在MgSi 2 O 6 H2-Al 2SiO 6 H2和MgSiO 4 H2 - 2 δ AlOOH + SiO2之间，每个相都有一个宽的固溶体系列，其中H相比D相更富铝。我们预测，除了Al相D和H稳定每个阶段通过额外的构型熵更高的温度。虽然我们已经表明，相H不表现出对称的氢键在高压下，我们在这里报告，相D经历了一个逐渐增加的对称H-键的数量开始在1030 GPa，它是只有1050%完成在60 GPa。
The degree to which the Earth’s mantle stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under mantle-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H, are stable to the pressures and temperatures of the Earth’s lower mantle, suggesting that the Earth’s lower mantle may participate in the cycling of water. We build on our prior work of density functional theory calculations on phase H with the stability, structure, and bonding of hydrous phases D, and we predict the aluminum partitioning with H in the Al 2 O 3 -SiO 2 -MgO-H 2 O system. We address the solid solutions through a statistical sampling of site occupancy and calculation of the partition function from the grand canonical ensemble. We show that each phase has a wide solid solution series between MgSi 2 O 6 H 2 -Al 2 SiO 6 H 2 and MgSiO 4 H 2 -2 δ AlOOH + SiO 2 , in which phase H is more aluminum rich than phase D at a given bulk composition. We predict that the addition of Al to both phases D and H stabilizes each phase to higher temperatures through additional configurational entropy. While we have shown that phase H does not exhibit symmetric hydrogen bonding at high pressure, we report here that phase D undergoes a gradual increase in the number of symmetric H-bonds beginning at ∼30 GPa, and it is only ∼50% complete at 60 GPa.