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Iron-titanium oxyhydroxides as water carriers in the Earth's deep mantle

Yu Nishihara and Kyoko N. Matsukage
Iron-titanium oxyhydroxides as water carriers in the Earth's deep mantle
American Mineralogist (April 2016) 101 (4): 919-927


We experimentally explored phase relations in the system FeOOH-TiO (sub 2) at pressures of 16 GPa and temperatures of 1000-1600 degrees C, which corresponds to conditions of the Earth's mantle transition zone. Analyses of the recovered samples revealed that, in the studied conditions, there are two stable iron-titanium oxyhydroxide phases whose estimated composition is expressed by (FeH) (sub 1-x) Ti (sub x) O (sub 2) . One is the Fe-rich solid solution (x < 0.23) with epsilon -FeOOH type crystal structure (orthorhombic, P2 (sub 1) nm), and the other is the more Ti-rich solid solution (x > 0.35) with alpha -PbO (sub 2) type structure (orthorhombic, Pbcn). The epsilon -FeOOH phase is stable up to approximately 1100 degrees C irrespective of chemical composition, whereas the alpha -PbO (sub 2) type phase is stable up to 1500 degrees C for a composition of x = 0.5 and at least to 1600 degrees C for x = 0.75, and thus the alpha -PbO (sub 2) type phase is stable at average mantle temperature in the Earth's mantle transition zone. Iron-titanium-rich phases found previously in basalt + H (sub 2) O system are estimated to be the epsilon -FeOOH and alpha -PbO (sub 2) type phases where the phase with iron-rich composition found at relatively low temperature (<1100 degrees C) is epsilon -FeOOH phase and the phase with titanium-rich composition is alpha -PbO (sub 2) type phase. The alpha -PbO (sub 2) type and epsilon -FeOOH phases may be stable in the subducted basaltic crust at pressures in the mantle transition zone under water-rich conditions.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 4
Title: Iron-titanium oxyhydroxides as water carriers in the Earth's deep mantle
Affiliation: Ehime University, Geodynamics Research Center, Ehime, Japan
Pages: 919-927
Published: 201604
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 37
Accession Number: 2016-040350
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Tokyo Institute of Technology, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201620
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