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Raman spectroscopy of the 10-Aa phase at simultaneously HP-HT

Paola Comodi, Fabio Cera, Sabrina Nazzareni and Leonid Dubrovinsky
Raman spectroscopy of the 10-Aa phase at simultaneously HP-HT (in EMPG XI; Experimental mineralogy, petrology and geochemistry symposium, Jonathan D. Bundy (editor), Simon C. Kohn (editor) and Michael J. Walter (editor))
European Journal of Mineralogy (October 2007) 19 (5): 623-629


Raman and X-ray diffraction data demonstrated that the 10-Aa phase is compressed metastably up to 42 GPa at room conditions and that water molecules remain between the sheets, forming hydrogen bonds (Comodi et al., 2006). The effect of temperature on the pressure evolution of the 10-Aa phase, Mg (sub 3) Si (sub 4) O (sub 10) (OH) (sub 2) H (sub 2) O, was studied by collecting Raman spectra simultaneously at high pressure (up to 27 GPa) and high temperature (up to 776 K) in electrically heated diamond-anvil cells. The Raman frequencies of all low-frequency modes (between 100 and 1200 cm (super -1) ) increased monotonically with pressure and slightly decreased with temperature along different isobars. The shift of the stretching bands of H (sub 2) O was opposite with P and T increase: the frequency of the 3597 cm (super -1) mode decreased with pressure (dnu /dP = -0.81 cm (super -1) GPa (super -1) ) and increased with temperature (dnu /dT = 0.025 cm (super -1) K (super -1) ), whereas the frequency of the 3673 cm (super -1) mode increased with P (dnu /dP = -1.38 cm (super -1) GPa (super -1) ) and decreased with T (dnu /dT = -0.011 cm (super -1) K (super -1) ). The hydroxyl stretching frequency at 3623 cm (super -1) increased with both P and T. The FWHM of the low-frequency modes, was independent from temperature and increased linearly with pressure up to 22 GPa, where Raman signals disappeared. Reversible behaviour indicated that no major reconstructive transition, such as amorphization occurred in the pressure-temperature range investigated. Temperature strongly affected the FWHM of the 3597 cm (super -1) mode, which disappeared at 570 K and 9 GPa, whereas at room temperature it was followed to about 12 GPa. The broadening of the OH-stretching was modelled with a progressive pressure-induced H disordering as observed in other hydrous minerals. Thus the 10-Aa phase should undergo to an order-disorder phase transition at 12 GPa and room temperature. The increase of temperature reduced the pressure at which the transition occurred. The measured mode shifts were used to determine isothermal and isobaric Gruneisen mode parameters, which were significantly higher than those of talc. The low values of the average calculated intrinsic anharmonic parameters, {a (sub i) }, of 0.52X10 (super -5) K (super -1) , indicated that a quasi-harmonic vibrational model may be used to describe the thermochemical properties of the 10-Aa phase. HP-HT Raman spectra indicate that the 10-Aa phase can host water at high P/T gradients and that it is a good candidate to transfer water in the mantle beyond the antigorite stability field.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 19
Serial Issue: 5
Title: Raman spectroscopy of the 10-Aa phase at simultaneously HP-HT
Title: EMPG XI; Experimental mineralogy, petrology and geochemistry symposium
Author(s): Comodi, PaolaCera, FabioNazzareni, SabrinaDubrovinsky, Leonid
Author(s): Bundy, Jonathan D.editor
Author(s): Kohn, Simon C.editor
Author(s): Walter, Michael J.editor
Affiliation: Universita di Perugia, Dipartimento di Scienze della Terra, Perugia, Italy
Pages: 623-629
Published: 200710
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: Eleventh international symposium on Experimental mineralogy, petrology and geochemistry
Meeting location: Bristol, GBR, United Kingdom
Meeting date: 20060911Sept. 11-13, 2006
References: 27
Accession Number: 2008-002130
Categories: Geophysics of minerals and rocks
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Universitat Bayreuth, DEU, Federal Republic of Germany
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200802
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