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Raman scattering of omphacite at high pressure; towards its possible application to elastic geothermobarometry

Lisa Baratelli, Mara Murri, Matteo Alvaro, Mauro Prencipe, Boriana Mihailova and Fernando Camara
Raman scattering of omphacite at high pressure; towards its possible application to elastic geothermobarometry
American Mineralogist (April 2024) Pre-Issue Publication

Abstract

Due to their widespread occurrence in several geological settings, omphacite inclusions could be used for elastic Raman geothermobarometry. However, the Raman scattering of complex silicate minerals entrapped in a host depends on both the chemical composition and elastic strain developed during the metamorphic pathway, which makes the task very challenging. Here, as a very first step to probe the potential of omphacite to be used as a mineral inclusion in elastic geothermobarometry, we report the pressure dependence of the Raman spectra of omphacite crystals with the same composition, approximately Jd (sub 45) Di (sub 55) , but having different symmetry because of the existence (P2/n) or absence (C2/c) of chemical order at the six- and eight-coordinated cation sites. The experimental results are complemented by ab initio quantum mechanical simulations on fully ordered omphacite (Jd (sub 50) Di (sub 50) ). We demonstrate that the position of the well-resolved Raman peak near 688 cm (super -1) , arising from Si-O-Si bond bending, is very sensitive to pressure but independent of the state of chemical order, which makes it promising to be utilized in Raman geobarometry. The width of this peak varies with chemical order but not with pressure and therefore can be used to constrain the temperature of inclusion entrapment, because the chemical order is indicative of the closure temperature of the cation-exchange reaction. However, further detailed analyses on the compositional variation of the Raman spectra of omphacite is required before considering omphacite-in-garnet systems as suitable for Raman elastic geothermobarometry.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: Pre-Issue Publication
Title: Raman scattering of omphacite at high pressure; towards its possible application to elastic geothermobarometry
Affiliation: University of Milan, Department of Earth Sciences, Milan, Italy
Published: 20240405
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 80
Accession Number: 2024-030129
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables
N47°40'00" - N50°34'60", E09°30'00" - E13°45'00"
Secondary Affiliation: University of Pavia, Department of Earth and Environmental Sciences, ITA, ItalyUniversity of Turin, ITA, ItalyUniversitaet Hamburg, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2024
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