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Possible H2O Storage in the Crystal Structure of CaSiO3 Perovskite
Physics of the Earth and Planetary Interiors ( IF 2.4 ) Pub Date : 2020-02-01 , DOI: 10.1016/j.pepi.2019.106412
H. Chen , K. Leinenweber , V. Prakapenka , C. Prescher , Y. Meng , H. Bechtel , M. Kunz , S.-H. Shim

Abstract The lower mantle is believed to contain much less hydrogen (or H2O) because of the low storage capacity of the dominant mineral phases, such as bridgmanite and ferropericlase. However, possible hydrogen storage in the third most abundant mineral in the region, CaSiO3 perovskite (Ca-Pv), is not well unknown. We have synthesized Ca-Pv from different starting materials with varying H2O contents at 19–120 GPa and 1400–2200 K in laser-heated diamond-anvil cell. While cubic perovskite structure is stable at the mantle-related pressures-temperatures (P−T) in anhydrous systems, we found non-cubic diffraction peak splitting in Ca-Pv even at high temperatures when it is synthesized from hydrous starting materials. In-situ high-pressure infrared spectroscopy showed OH vibration possibly from Ca-Pv. The unit-cell volume of hydrothermally synthesized Ca-Pv is systematically smaller than that of anhydrous Ca-Pv at high pressures. These observations suggest possible H2O storage in Ca-Pv at mantle-related P−T conditions. We also found the formation of separate δ–AlOOH and Ca-Pv phases from Al-bearing CaSiO3 glass starting materials in an H2O medium at 60 GPa and 1400 K. Ca-Pv still showed non-cubic peak splitting at high temperatures in this experiment. Therefore, it is possible that hydrous phases may coexist together with hydrous Ca-Pv in the lower mantle.

中文翻译:

CaSiO3钙钛矿晶体结构中可能存在的H2O储存

摘要 下地幔被认为含有更少的氢(或 H2O),因为主要矿物相(如桥锰矿和铁方镁石)的储存能力低。然而,该地区第三丰富的矿物 CaSiO3 钙钛矿 (Ca-Pv) 中可能储存的氢还不是很清楚。我们在激光加热的金刚石砧电池中从不同的起始材料合成了 Ca-Pv,在 19-120 GPa 和 1400-2200 K 下具有不同的 H2O 含量。虽然立方钙钛矿结构在无水系统中与地幔相关的压力-温度 (P-T) 下是稳定的,但我们发现,即使在高温下,当它由含水起始材料合成时,Ca-Pv 中的非立方衍射峰也会分裂。原位高压红外光谱显示可能来自 Ca-Pv 的 OH 振动。在高压下,水热合成的 Ca-Pv 的晶胞体积系统地小于无水 Ca-Pv 的晶胞体积。这些观察结果表明,在与地幔相关的 P-T 条件下,Ca-Pv 中可能存在 H2O 储存。我们还发现在 60 GPa 和 1400 K 的 H2O 介质中,含铝的 CaSiO3 玻璃起始材料形成了单独的 δ-AlOOH 和 Ca-Pv 相。在该实验中,Ca-Pv 在高温下仍显示出非立方峰分裂. 因此,水合相可能与下地幔中的水合 Ca-Pv 共存。我们还发现在 60 GPa 和 1400 K 的 H2O 介质中,含铝的 CaSiO3 玻璃起始材料形成了单独的 δ-AlOOH 和 Ca-Pv 相。在该实验中,Ca-Pv 在高温下仍显示出非立方峰分裂. 因此,水合相可能与下地幔中的水合 Ca-Pv 共存。我们还发现在 60 GPa 和 1400 K 的 H2O 介质中,含铝的 CaSiO3 玻璃起始材料形成了单独的 δ-AlOOH 和 Ca-Pv 相。在该实验中,Ca-Pv 在高温下仍显示出非立方峰分裂. 因此,水合相可能与下地幔中的水合 Ca-Pv 共存。
更新日期:2020-02-01
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