High‐Pressure Transformations and Stability of Ferromagnesite in the Earth's Mantle

Abstract We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” [CaAl4Si2O11], honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth's mantle. Donwilhelmsite forms in the Earth's mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.

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High-pressure Single-crystal X-ray Diffraction Study on Minerals Related to the Earth's Mantle:

Nihon Kessho Gakkaishi ◽

10.5940/jcrsj.60.32 ◽

2018 ◽

Vol 60 (1) ◽

pp. 32-39

Author(s):

Atsushi KYONO

Keyword(s):

High Pressure ◽

Single Crystal ◽

Diffraction Study ◽

X Ray Diffraction ◽

X Ray ◽

Earth’S Mantle

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Comment on K. Mibe, T. Fujii, and A. Yasuda (2002), “Composition of aqueous fluid coexisting with mantle minerals at high pressure and its bearing on the differentiation of the earth’s mantle,” Geochimica et Cosmochimica Acta 66,2273–2285

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2003.01.001 ◽

2004 ◽

Vol 68 (4) ◽

pp. 927-928 ◽

Cited By ~ 2

Author(s):

Roland Stalder

Keyword(s):

High Pressure ◽

Aqueous Fluid ◽

Mantle Minerals ◽

Earth’S Mantle

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1611571113 ◽

2016 ◽

Vol 113 (49) ◽

pp. 13971-13976 ◽

Cited By ~ 16

Author(s):

Andreas Hermann ◽

Mainak Mookherjee

Keyword(s):

High Pressure ◽

Transition Zone ◽

Lower Mantle ◽

Direct Detection ◽

Geophysical Methods ◽

High Pressure Phase ◽

Mantle Transition Zone ◽

Earth’S Mantle ◽

3D Network ◽

Pressure Phase

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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High-Pressure Elastic Constant of Some Materials of Earth’s Mantle

Zeitschrift für Naturforschung A ◽

10.1515/zna-2015-0487 ◽

2016 ◽

Vol 71 (5) ◽

pp. 433-437

Author(s):

Quan Liu

Keyword(s):

Experimental Data ◽

High Pressure ◽

Theoretical Model ◽

Elastic Behaviour ◽

Exponential Relationship ◽

Earth’S Mantle ◽

Simple Theoretical Model ◽

Volume Dependence ◽

Theoretical Investigations ◽

Good Agreement

AbstractIn the present work, an exponential relationship for the volume dependence of the Anderson–Grüneisen parameter along isotherm and the formulation derived from Tallon’s model have been used to develop a simple theoretical model for the elastic constants as a function of pressure. Applying it to some materials of earth’s mantle at different pressure ranges, the calculated results are in good agreement with the earlier theoretical investigations and available experimental data and thus show that our theory can be applied for predicting the elastic behaviour of earth materials at high pressure.

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