Compression and structure of brucite to 31 GPa from synchrotron X-ray diffraction and infrared spectroscopy studies

Ma, Maining; Liu, Wei; Chen, Zhiqiang; Liu, Zhenxian; Li, Baosheng

doi:10.2138/am.2013.4117

Cited by 21 publications

(20 citation statements)

References 28 publications

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“…This agrees reasonably well with thermodynamic modeling based on the measured P-V-T equation of state for brucite, which estimated a decomposition pressure of 27 GPa at T = 300 K (24). Note that brucite has been compressed significantly beyond this pressure, likely due to kinetic barriers in the decomposition reaction (24,25).…”

Section: Resultssupporting

confidence: 87%

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

Hermann

Mookherjee

2016

Proc. Natl. Acad. Sci. U.S.A.

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We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH) 2 , using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth's mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth's interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO 6 octahedral units arranged in the anatase-TiO 2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.brucite | pressure | phase transition | electronic structure calculations W ater plays an important role in sustaining geological activity. For instance, water helps in lowering the mantle's melting temperature, enhancing diffusion and creep thus affecting rheology of rocks, and also influences mineral phase boundaries. Current estimates suggest that the Earth's mantle is likely to contain a mass of water equivalent to the mass of the world's oceans (1, 2). The exchange of water between the surface and deep mantle reservoirs is vital for the sustenance of surface water over geological time scales (3). Hydrous minerals stable in the hydrated oceanic crust and mantle play an important role in transporting water into the Earth's interior. Hydrated peridotite, the major mantle rock type, can be understood by considering mineral phases stable in the ternary system of MgO-SiO 2 -H 2 O (MSH). Brucite, Mg(OH) 2 , is arguably the simplest hydrous mineral in the MSH system. Brucite is also the most important MgO-H 2 O binary and the most water-rich phase within the MSH ternary system.The crystal structure of brucite consists of Mg 2+ cations and OH − anions arranged in layers, in an overall trigonal structure (space group symmetry P 3m1); Fig. 1. The common ionic compound CdI 2 is the archetype crystal structure for brucite as well as for portlandite [Ca(OH) 2 )] and several other transition metal hydroxides M(OH) 2 where M = Mn, Ni, Co, Fe, Cd,. In brucite, the crystal structure comprises layers of edge-sharing MgO 6 polyhedra. The interaction between the layers is weak at ambient conditions, where each upward-pointing OH group is surrounded by three downward-pointing OH groups in the adjacent layer and vice versa. Under compression the H-H repulsive interactions lead to positional disordering of the protons, which are displaced from the 2d Wyckoff site into one of three equivalent 6i sites as documented from neutron diffraction studies (11,12). Vibrational spectroscopic studies incl...

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Section: Resultssupporting

confidence: 87%

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

Hermann

Mookherjee

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Optimized results were fitted by the Birch‐Murnaghan equation of state (Birch, ). As the fitted parameters were in good agreement with previous studies (Duffy et al, ; Fei & Mao, ; Fukui et al, ; Hermansson et al, ; Horita et al, ; Ma et al, ; Mitev et al, ; Mookherjee & Stixrude, ; Nagai et al, ; Parise et al, ; Xia et al, ; see Text S1, Figure S1, and Tables S1 and S2 in the supporting information), the computational conditions described above were applied to all the calculations performed in this study. Figures of crystals were drawn with VESTA (Momma & Izumi, ).…”

Section: Methodssupporting

confidence: 80%

First‐principles Investigation of Frictional Characteristics of Brucite: An Application to Its Macroscopic Frictional Characteristics

2019

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Because sheet-structure minerals are often observed in natural faults and have lower friction coefficients than the other common rocks and rock-forming minerals, it has been suggested that their frictional characteristics are related to fault strength. Despite their importance for understanding fault dynamics, what controls their frictional characteristics has not been clarified yet. Because the friction coefficients of these minerals depend on the mineral species, the atomic-scale crystal structure can be a clue for understanding the mechanism. In this study, the variation of potential energy on the brucite (0001) shear plane (potential energy surface, PES) was calculated by using first-principles calculations based on density functional theory. The shear stress along the sliding path is calculated by computing the displacement derivative of the PES. According to the adhesion theory of friction, we found that the atomic-scale frictional parameters obtained by using the PES could explain the macroscopic friction coefficients when taking the experimental indentation strength into account. Then, we propose how to estimate the constitutive parameter a of the rate-and state-dependent friction law from the PES of sheet-structure minerals. The estimated value is consistent with the typical range for minerals investigated by previous experiments. The difference in the PES among sheet-structure minerals can therefore be a key property to explain their frictional characteristics such as the tendency for frictional instability of natural faults.

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“…Synchrotron-generated IR radiation is much brighter (∼ 1000×) than conventional globar sources of commercial FTIR instruments, and high-quality IR spectra can readily be measured through small (10 µm) apertures (Lobo et al, 1999;Carr et al, 2008;Ma et al, 2013). By coupling synchrotron radiation to a FTIR instrument and IR microscope, OH absorption bands can be measured through a 10 µm aperture with higher signal-to-noise ratio than through a 100 µm aperture using a standard FTIR system.…”

Section: Methodsmentioning

confidence: 99%

Synchrotron FTIR imaging of OH in quartz mylonites

et al. 2017

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Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4-8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm 2 . This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm −1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm −1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm −1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

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Compression and structure of brucite to 31 GPa from synchrotron X-ray diffraction and infrared spectroscopy studies

Cited by 21 publications

References 28 publications

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

First‐principles Investigation of Frictional Characteristics of Brucite: An Application to Its Macroscopic Frictional Characteristics

Synchrotron FTIR imaging of OH in quartz mylonites

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