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Schematic diagram of ORP in the DLM. Hydrous minerals in the subducting slab (blue) carry H 2 O to react with the iron core to form the ORP (dark brown) which is a multilayer with increasing oxygen content (inset). H 2 O penetrates the multilayer to produce more Py-phase, and hydrogen escapes from FeH and FeO 2 Hx and ascends upwards to sustain the hydrogen cycle. The ORP moves laterally and accumulates. Some ORP (small patches) are scattered and mixed with the DLM silicates and oxides.
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Hydrous minerals in subducted crust can transport large amounts of water into Earth's deep mantle. Our laboratory experiments revealed the surprising pressure-induced chemistry that, when water meets iron at the core–mantle boundary, they react to form an interlayer with an extremely oxygen-rich form of iron, iron dioxide, together with iron hydrid...
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... and oxides substantially. Moreover, spatial distribution in ORP are expected to be very uneven (Fig. 4) and some re- gions can be much ...
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... from its point of generation at the cooler down- going slab to hotter regions [18] following the whole mantle convection. Due to the density contrast, it will not rise with the plume, but will reside and grow indefinitely. Analogous to the isostasy of continental crust on the mantle, the bottom of a very thick ORP would dip into the outer core (Fig. ...
Citations
... Water can induce melting and melt migration, and hydration of lowermost mantle materials, which might create the large low-shear-velocity provinces 1,31 . Furthermore, the reaction of water with core metal may form superoxidized FeOOH x (x < 1) [32][33][34] , which could account for the ultralow-velocity zones 35 . Also, it might develop a low-velocity layer in the topmost core 36,37 . ...
... The dehydration of subducted slabs at the base of the mantle has been stressed, and its consequences have been extensively discussed 1,2,34,37,50 . However, our finding of the high capacity for H 2 O (~2 wt% in α-PbO 2 -type SiO 2 and ~0.3-0.6 wt% in subducted MORB crust) suggests that practically water does not escape from slabs under the high temperatures of the CMB region. ...
The hydrated SiO2 phase is a main carrier of water in subducting slabs in the lower mantle. Assuming its dehydration at high temperatures above the core–mantle boundary, it has been speculated that seismic anomalies observed in this enigmatic region and the uppermost core might be attributable to water released from slabs. Here we report melting experiments on a hydrous basalt up to conditions of the core–mantle boundary region at 25–144 GPa and 2,900–4,100 K. Secondary-ion mass spectrometry measurements with high-resolution imaging techniques reveal that the SiO2 phase and SiO2–AlOOH solid solution contain 0.5–3.6 wt% and ~3.5 wt% H2O, respectively, coexisting with melts holding 0.9–2.6 wt% H2O. The high solubility into SiO2 and high SiO2/melt partition coefficient of water at the high temperatures of the core–mantle boundary region suggest that practically water does not escape from subducted slabs at the base of the mantle. Even if the core–mantle boundary temperature were high enough to melt subducted crustal materials, most of the H2O would remain in the solid residue rather than entering a partial melt. Previously proposed consequences of slab dehydration are therefore unlikely to be responsible for chemical heterogeneities in the lowermost mantle and the topmost core.
... The spin transition of iron holds fundamental significance for mantle physics, as it impacts the density, elasticity, element partitioning and transport properties of major mantle minerals (Lin et al. 2013;Badro 2014). Recent studies demonstrated that FeO 2 and FeO 2 H x (x ≤ 1) phases might exist in the deep lower mantle, potentially accounting for the global oxygen-hydrogen cycles (Hu et al. 2016;Liu et al. 2017;Mao et al. 2017;Nishi et al. 2017;Yuan et al. 2018). These unique iron oxide-hydroxide compounds were initially thought to be related to the pyrite structure, while the latest single-crystal X-ray diffraction data indicated they align more closely with the HP-PdF 2 -type structure (Koemets et al. 2021). ...
Iron hydroxide FeO2Hx (x ≤ 1) and ferrous iron chloride FeCl2 can adopt the HP-PdF2-type (space group: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P{a_{\overline 3 }}$$\end{document}, Z = 4) structure in the lowermost mantle, potentially contributing to the geochemical cycles of hydrogen and chlorine within Earth’s deep interior, respectively. Here we investigate the high-pressure behavior of HP-PdF2-type FeCl2 by X-ray diffraction (XRD) and Raman measurements in laser-heated diamond anvil cells. Our results show that HP-PdF2-type FeCl2 can be formed at 60‒67 GPa and 1650‒1850 K. Upon cold decompression, the diffraction peaks at pressures above 10 GPa can be indexed to the HP-PdF2-type structure. Intriguingly, the calculated cell volumes reveal a remarkable decrease of ΔV / V = ∼ 14% between 36 and 40 GPa, which is possibly caused by a pressure-induced spin transition of Fe²⁺ (HS: high-spin → LS: low-spin). We also observe distinct changes in Raman spectra at 33‒35 GPa, practically coinciding with the onset pressures of isostructural phase transition in XRD results. Our observations combined with previous studies conducted at megabar pressures suggest that HP-PdF2-type FeCl2, with a wide pressure stability range, if present in subducting slabs, could facilitate the transport of chlorine from the middle lower mantle to the outer core.
... ULVZs normally are several tens of kilometers thick and may yield P-wave and S-wave velocity reduction by up to ∼10% and ∼30%, respectively (McNamara, 2019). In general, two theories are widely acknowledged to interpret the existence of ULVZ at Earth's lower mantle: (a) partial melt occurs at the location of ULVZ other than the ambient mantle (Ohtani & Maeda, 2001;Wen & Helmberger, 1998;Williams & Garnero, 1996); (b) core rust is formed when iron interacts with water or hydroxide minerals at the lower mantle (Hu et al., 2016;Liu et al., 2017;Mao et al., 2017). The low-velocity layer near the Martian CMB observed in our study (Figure 4) may follow the same theories as the ULVZ observed on Earth. ...
Plain Language Summary
The InSight mission deployed one seismic station on Mars at the end of 2018 to measure the interior structure of Mars. A recent study autocorrelated the InSight ambient noise data to retrieve reflection signals from subsurface discontinuities. Two seismic signals that reflected from deep within Mars, the olivine‐wadsleyite transition, a pressure‐temperature dependent mineral phase change in the mantle, and the core‐mantle boundary (CMB), are observed. However, some analyses suggested that the arrival times of these signals coincide with the recurrence time of high‐amplitude glitches within the raw seismic data, leading to an incorrect interpretation of the autocorrelation function (ACF). To resolve this issue, we detected and removed the high‐amplitude glitches before further processing the ambient noise data. The autocorrelation analysis of clean continuous vertical‐component waveforms recovers signals at times corresponding to the olivine‐wadsleyite transition and CMB, whereas ACF of glitch‐only waveforms does not. This suggests that signals on the low‐frequency ACF are from the seismic discontinuities at olivine‐wadsleyite transition and CMB rather than being noise artifacts. We further identified velocity layering near Martian CMB by matching the complexity of the PcP signal observed in the ACF of clean data set with synthetic seismograms.
... FeOOH, an abundant water-bearing mineral found in the Earth's crust and mantle, exerts significant influence over terrestrial life and crucial physical and chemical processes within the planet's interior [1]. Recent studies reveal the capacity of FeOOH to transport water deeply into the Earth's interior via subducting slabs [2,3], accompanied by a complex series of structural phase transitions. Under ambient pressure, FeOOH is stable as the goethite phase (α-FeOOH) [4,5]; both akaganeite (β-FeOOH) and lepidocrocite (γ -FeOOH) are metastable phases [6,7]. ...
Investigating hydrogen bond symmetrization in hydroxyl compounds necessitates the precise determination of crystal microstructures. Nonetheless, H atoms are nearly indistinguishable in experiments, posing a challenge to unraveling the formation mechanism of this phenomenon. A deep learning potential model was used for classical molecular dynamics simulations of the hydrogen bond symmetrization process of ɛ-FeOOH in this study. Through calculations of the H–O bond length, it has been determined that the system undergoes hydrogen bond symmetrization when the pressure reaches 40.25 GPa. The volume thermal expansion curve of ɛ-FeOOH exhibits anomalies due to the proton-disordering phase transition, and the pressure for this transition shows a negative correlation with temperature. The calculated results of the O1⋯O2 bond length indicate that an increase in temperature will lead to an increase in the critical pressure for hydrogen bond symmetrization while reducing the distinction between the hydrogen bond symmetrization structure and the proton-disordered structure. In addition, the spin transition of Fe atoms at lower temperatures is unrelated to hydrogen bond symmetrization. However, with increasing temperature, the spin transition may potentially promote hydrogen bond symmetrization.
... The H 2 O released from these hydrous minerals can react with iron at the CMB. The reaction between Fe and H 2 O has been extensively studied at high pressures [1,[28][29][30]. At pressures below 70 GPa, ...
... In the presence of water (hydrous minerals) and metallic Fe, FeH can be formed and transported to the deepest mantle by mantle convection. On the other hand, water can be brought to the deepest lower mantle by ultra-dense hydrous phases [29,68]. Thus, FeH can be produced by the reaction of the released water and Fe from the core (Eq. ...
... This process also generates significant amounts of FeO 2 and FeO 2 H x , which are less dense than FeH and can be deposited as oxygen-rich patches (ORP) above the CMB. The accumulation of the ORP provides an explanation for the formation of the ULVZ, and the eruption of the ORP may have impacted the Great Oxidation Event [29,69]. Superionic fcc FeH x is stable under the conditions of the lowermost mantle and D 00 layer (the lowermost portion of the mantle). ...
Iron hydride in Earth's interior can be formed by the reaction between hydrous minerals (water) and iron. Studying iron hydride improves our understanding of hydrogen transportation in Earth's interior. Our high-pressure experiments found that face-centered cubic (fcc) FeHx (x ≤ 1) is stable up to 165 GPa, and our ab initio molecular dynamics simulations predicted that fcc FeHx transforms to a superionic state under lower mantle conditions. In the superionic state, H-ions in fcc FeH become highly diffusive-like fluids with a high diffusion coefficient of ∼3.7 × 10-4 cm2 s-1, which is comparable to that in the liquid Fe-H phase. The densities and melting temperatures of fcc FeHx were systematically calculated. Similar to superionic ice, the extra entropy of diffusive H-ions increases the melting temperature of fcc FeH. The wide stability field of fcc FeH enables hydrogen transport into the outer core to create a potential hydrogen reservoir in Earth's interior, leaving oxygen-rich patches (ORP) above the core mantle boundary (CMB).
... Water is transported to the deep part of the earth in the subduction zone of the subducting plate [91], where it reacts with iron under different temperature and pressure conditions to form a unique high-magnesium iron hydride [92,93]. Finally, dehydrogenation takes place and hydrogen-rich fluids in the mantle return to the surface through volcanic hydrothermal activity [94,95]. ...
Recent research in the field of oil and gas geochemistry has focused on the catalytic role of minerals in geological history. Thermal simulation experiments are considered a valuable means of studying the formation and transformation of hydrocarbons. In this paper, we review the catalytic mechanisms, processes, and various arguments for different types of minerals in thermal simulation experiments from the perspective of mineral additives. We focus on two categories: (1) minerals that provide direct catalysis, such as clay minerals, alkali metals, carbonate rocks, and some transition metal elements, and (2) minerals, such as serpentine, that promote aqueous hydrogen and act as the material basis, as well as the radioactive element uranium. We also discuss existing disputes and prospects for the development direction of mineral catalytic thermal simulation experiments.
... Of particular interest is the behavior of electrons with respect to extremes such as high pressure, leading to novel phenomena of insulator-metal transitions, superconductivity, highly reactive atoms and abnormal physiochemical properties of condensed matters 4,5 . Numerous well-designed experimental, computational and theoretical studies in chemistry, physics, material sciences and geosciences have provided insights into the unusual phenomena associated with pressure-induced electronic behavior [5][6][7] . However, the general rules that drive electron transfer at high pressure remain to be revealed. ...
... In planetary sciences, the mineral work function has been applied to interprete the electrostatic migration of charging lunar dust, the contact electrification phenomenon during electrical beneficiation and the energy threshold of emitting photoelectrons [13][14][15] . The electronegativity of atoms and work function of minerals could also be applied to quantitatively evaluate the electron transfer tendency and directions under high pressures such as explaining some intricate redox interactions among minerals, fluids, melts and volatiles in Earth's deep region up to~350 gigapascals (GPa) 6,16 . Nevertheless, both the electronegativity and work function may be greatly changed when compressed, ascribed to the pressure-induced changes in electronic states 4,5 . ...
... At the mineral phase boundary, electrons will spontaneously flow from the phase with lower work function to the other 29,30 , thus driving a possible redox reaction. Inside the Earth, the reactivity of minerals with water is vital to our understanding of deep element cycle 6,31,32 . Actually, natural oxides and silicates account for more than 90% of the total weight of Earth's crust. ...
Electron transfer is the most elementary process in nature, but the existing electron transfer rules are seldom applied to high-pressure situations, such as in the deep Earth. Here we show a deep learning model to obtain the electronegativity of 96 elements under arbitrary pressure, and a regressed unified formula to quantify its relationship with pressure and electronic configuration. The relative work function of minerals is further predicted by electronegativity, presenting a decreasing trend with pressure because of pressure-induced electron delocalization. Using the work function as the case study of electronegativity, it reveals that the driving force behind directional electron transfer results from the enlarged work function difference between compounds with pressure. This well explains the deep high-conductivity anomalies, and helps discover the redox reactivity between widespread Fe(II)-bearing minerals and water during ongoing subduction. Our results give an insight into the fundamental physicochemical properties of elements and their compounds under pressure.
... Previous experimental results show that adding water into the multi-component systems could significantly change phase relations in the lower mantle systems and alter phase chemistry in the assemblages (Ohira et al. 2014;Walter et al. 2015;Yuan et al. 2019). The pyrite-structured phase FeO 2 H x (x ≤ 1, Pyphase) has been synthesized through reactions between water and iron in a wide range of oxidation states, from Fe to Fe 2 O 3 , at pressures above 85 GPa under high-temperature conditions (Hu et al. 2016;Mao et al. 2017;Nishi et al. 2017;Yuan et al. 2018), indicating that the formation of Py-phase is independent of the oxidation state of iron in starting materials. Furthermore, the Py-phase was observed coexisting with bridgmanite (Bdg) or post-perovskite (pPv) through reaction between Fe-bearing olivine and water (Chen et al. 2020;Hu et al. 2021). ...
The presence of water may contribute to compositional heterogeneities observed in the deep lower mantle. Mg-rich ferropericlase (Fp) (Mg,Fe)O in the rock-salt structure is the second most abundant phase in a pyrolitic lower mantle model. To constrain water storage in the deep lower mantle, experiments on the chemical reaction between (Mg,Fe)O and H2O were performed in a laser-heated diamond-anvil cell at 95–121 GPa and 2000–2250 K, and the run products were characterized combining in situ synchrotron X-ray diffraction measurements with ex-situ chemical analysis on the recovered samples. The pyrite-structured phase FeO2Hx (x ≤ 1, Py-phase) containing a negligible amount of Mg (<1 at%) was formed at the expense of iron content in the Fp-phase through the reaction between (Mg,Fe)O and H2O, thus serving as water storage in the deepest lower mantle. The formation and segregation of nearly Mg-free Py-phase to the base of the lower mantle might provide a new insight into the deep oxygen and hydrogen cycles.
... 板块俯冲物质不仅可以到达地幔过渡带, 而且还 可以到达核幔边界的上部, 特别是地幔的D″层, 那里成 了"板片的坟场" [12] . 到达地幔D″层的板片是发源于核 幔边界地幔柱的重要物质组成, 地幔D″层因而是地球 深部过程与表层系统相互作用的一个关键地带. 实验 岩石学研究显示, 不仅在地幔过渡带, 甚至在核幔边界 都存在含水矿物组合 [13,14] . 这些都显示了表层系统对 深部过程影响的深度之大和范围之广. ...
... [17] . 矿物晶格水通过俯冲可以到达下地幔底部, 在核 幔边界释放出来后, 会与地球外核的Fe发生反应, 形成 一层铁的极端富氧形式矿物 [13,14,18] . ...
... If water-rich ambient mantle ascends out of the mantle transition zone into a zone of low-water-solubility, it may undergo dehydration-induced partial melting, thereby filtering incompatible elements out of the depleted rising material (Bercovici and Karato 2003). Finally, water transported into the deepest mantle could lead to chemical reactions with iron-rich materials (e.g., Yuan et al. 2018) that may possibly trigger large-scale geodynamic events (Mao et al. 2021). ...
The dynamics and evolution of Venus’ mantle are of first-order relevance for the origin and modification of the tectonic and volcanic structures we observe on Venus today. Solid-state convection in the mantle induces stresses into the lithosphere and crust that drive deformation leading to tectonic signatures. Thermal coupling of the mantle with the atmosphere and the core leads to a distinct structure with substantial lateral heterogeneity, thermally and compositionally. These processes ultimately shape Venus’ tectonic regime and provide the framework to interpret surface observations made on Venus, such as gravity and topography. Tectonic and convective processes are continuously changing through geological time, largely driven by the long-term thermal and compositional evolution of Venus’ mantle. To date, no consensus has been reached on the geodynamic regime Venus’ mantle is presently in, mostly because observational data remains fragmentary. In contrast to Earth, Venus’ mantle does not support the existence of continuous plate tectonics on its surface. However, the planet’s surface signature substantially deviates from those of tectonically largely inactive bodies, such as Mars, Mercury, or the Moon. This work reviews the current state of knowledge of Venus’ mantle dynamics and evolution through time, focussing on a dynamic system perspective. Available observations to constrain the deep interior are evaluated and their insufficiency to pin down Venus’ evolutionary path is emphasised. Future missions will likely revive the discussion of these open issues and boost our current understanding by filling current data gaps; some promising avenues are discussed in this chapter.
