Anomalous elastic behavior of phase egg, AlSiO3(OH), at high pressures
Anomalous elastic behavior of phase egg, AlSiO3(OH), at high pressures
复制标题
DOI：
10.2138/am-2019-6694
复制
发表时间：
2019-01
影响因子：
3.1
通讯作者：
M. Mookherjee;W. R. Panero;B. Wunder;S. Jahn
中科院分区：
文献类型：
--
作者：
M. Mookherjee;W. R. Panero;B. Wunder;S. Jahn
摘要相卵[AlSiO 3（OH）]是一种铝硅酸盐含水矿物，在以Al 2 O3-SiO2-H2O（ASH）三元体系为代表的岩性组成中，俯冲沉积物和大陆地壳岩石矿物学的简化三元系。高压和高温实验的岩石成分类似的水化沉积层在俯冲板片显示，相蛋是稳定的压力高达20-30 GPa，这转化为过渡带下地幔深度。因此，相蛋是一个潜在的候选人，为运输水到地球的地幔过渡带。在这项研究中，我们使用基于密度泛函理论的第一性原理模拟来探索晶体结构的压力依赖性以及它如何影响能量学和弹性。结果表明，在地幔过渡带深度（~15 GPa），相蛋具有弹性压力依赖性的反常行为。这种反常的弹性行为与氢键O-H···O构型的变化有关，我们将其描述为从低压到高压的相蛋结构的转变。全弹性常数张量表明，相位卵是非常各向异性的，导致在零压力下的纵波速度的最大各向异性，AvP <$30%和横波速度的最大各向异性，AvS <$17%。我们的研究结果还表明，相蛋具有最快的体积声速（vP和vS）相比，其他水合铝相在灰三元，其中包括黄玉-OH，相Pi，和δ-AlOOH。而相卵的体声速比斯氏石英慢。在对应于地幔过渡带底部的深度，相蛋分解为δ-AlOOH和斯铁闪石的混合物。与分解相关的纵波速度变化ΔvP和横波速度变化ΔvS分别为~0.42%和-1.23%。虽然相卵可能仅限于俯冲沉积物，但它可以保持沿着正常地幔地热的几个重量百分比的水。
Abstract Phase egg, [AlSiO3(OH)], is an aluminosilicate hydrous mineral that is thermodynamically stable in lithological compositions represented by Al2O3-SiO2-H2O (ASH) ternary, i.e., a simplified ternary for the mineralogy of subducted sediments and continental crustal rocks. High-pressure and high-temperature experiments on lithological compositions resembling hydrated sedimentary layers in subducting slabs show that phase egg is stable up to pressures of 20–30 GPa, which translates to the transition zone to lower mantle depths. Thus, phase egg is a potential candidate for transporting water into the Earth’s mantle transition zone. In this study, we use first-principles simulations based on density functional theory to explore the pressure dependence of crystal structure and how it influences energetics and elasticity. Our results indicate that phase egg exhibits anomalous behavior of the pressure dependence of the elasticity at mantle transition zone depths (~15 GPa). Such anomalous behavior in the elasticity is related to changes in the hydrogen bonding O-H···O configurations, which we delineate as a transition from a low-pressure to a high-pressure structure of phase egg. Full elastic constant tensors indicate that phase egg is very anisotropic resulting in a maximum anisotropy of compressional wave velocity, AvP ≈ 30% and of shear wave velocity, AvS ≈ 17% at zero pressures. Our results also indicate that the phase egg has one of the fastest bulk sound velocities (vP and vS) compared to other hydrous aluminous phases in the ASH ternary, which include topaz-OH, phase Pi, and δ-AlOOH. However, the bulk sound velocity of phase egg is slower than that of stishovite. At depths corresponding to the base of mantle transition zone, phase egg decomposes to a mixture of δ-AlOOH and stishovite. The changes in compressional ΔvP and shear ΔvS velocity associated with the decomposition is ~0.42% and –1.23%, respectively. Although phase egg may be limited to subducted sediments, it could hold several weight percentages of water along a normal mantle geotherm.