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Mookherjee, Mainak ORCID: 0000-0002-0605-5964, Panero, Wendy R., Wunder, Bernd and Jahn, Sandro ORCID: 0000-0002-2137-8833 (2019). Anomalous elastic behavior of phase egg, AlSiO3(OH), at high pressures. Am. Miner., 104 (1). S. 130 - 140. CHANTILLY: MINERALOGICAL SOC AMER. ISSN 1945-3027

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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 (similar to 15 GPa). Such anomalous behavior in the elasticity is related to changes in the hydrogen bonding O-H center dot center dot center dot 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, Av(P) approximate to 30% and of shear wave velocity, Av(S) approximate to 17% at zero pressures. Our results also indicate that the phase egg has one of the fastest bulk sound velocities (v(P) and v(S)) compared to other hydrous aluminous phases in the ASH ternary, which include topaz-OH, phase Pi, and delta-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 delta-AlOOH and stishovite. The changes in compressional Delta v(P) and shear Delta v(S) velocity associated with the decomposition is similar to 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.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Mookherjee, Mainak UNSPECIFIED orcid.org/0000-0002-0605-5964 UNSPECIFIED Panero, Wendy R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wunder, Bernd UNSPECIFIED UNSPECIFIED UNSPECIFIED Jahn, Sandro UNSPECIFIED orcid.org/0000-0002-2137-8833 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-140257
DOI:	10.2138/am-2019-6694
Journal or Publication Title:	Am. Miner.
Volume:	104
Number:	1
Page Range:	S. 130 - 140
Date:	2019
Publisher:	MINERALOGICAL SOC AMER
Place of Publication:	CHANTILLY
ISSN:	1945-3027
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EQUATION-OF-STATE; HYDROGEN-BOND SYMMETRIZATION; SINGLE-CRYSTAL ELASTICITY; AB-INITIO; ALUMINUM SILICATE; DELTA-ALOOH; SOUND VELOCITIES; STABILITY; MANTLE; WATER Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/14025