Calculation of the phase diagrams of the MgO–FeO–Al 2 O 3 –SiO 2 system at high pressures and temperatures: application to the mineral structure of the Earth's mantle transition zone

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 MgO6 octahedral units arranged in the anatase–TiO2 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.

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The thermodynamics of substances at very high pressures and temperatures and some mineral reactions in the earth's mantle

Physics and Chemistry of Minerals ◽

10.1007/bf00307547 ◽

1979 ◽

Vol 5 (2) ◽

pp. 105-118 ◽

Cited By ~ 13

Author(s):

I. A. Ostrovsky

Keyword(s):

High Pressures ◽

Earth’S Mantle ◽

High Pressures And Temperatures ◽

Very High

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Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite

Science ◽

10.1126/science.1259369 ◽

2014 ◽

Vol 346 (6213) ◽

pp. 1100-1102 ◽

Cited By ~ 134

Author(s):

Oliver Tschauner ◽

Chi Ma ◽

John R. Beckett ◽

Clemens Prescher ◽

Vitali B. Prakapenka ◽

...

Keyword(s):

Perovskite Structure ◽

High Pressures ◽

Solid Phase ◽

Phase Assemblage ◽

Half Century ◽

International Mineralogical Association ◽

Mineralogical Association ◽

Earth’S Mantle ◽

High Pressures And Temperatures ◽

Peak Shock

Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth’s mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

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