Plagioclase composition by Raman spectroscopy

Bersani, Danilo and Aliatis, Irene and Tribaudino, Mario and Mantovani, Luciana and Benisek, Artur and Carpenter, Michael A. and Gatta, Giacomo Diego and Lottici, Pier Paolo (2018) Plagioclase composition by Raman spectroscopy. Journal of Raman Spectroscopy. ISSN 03770486 DOI https://doi.org/10.1002/jrs.5340

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Abstract

Plagioclase undergoes complex exsolution and ordering and phase transition processes during their evolution in nature, and this has hindered attempts to define simple trends relating the major peaks of their Raman spectra with composition. Here, the peak position and linewidth of major Raman features have been calibrated for a set of 20 plagioclases, spanning from albite to anorthite in composition, with symmetry and ordering states that were already well characterized. Point group symmetry is the most important factor determining the Raman peak behaviour with composition, though C math formula, I math formula, and P math formula plagioclases show different trends for the position of the main peak νa at ~500 cm−1. Using a simplifying approach, which merges the effect of Al–Si ordering and incommensurate modulations, a method has been developed to estimate the plagioclase composition from calibration of a few determinative Raman peaks. This makes use of the wavenumber difference Δab between the most intense peaks νa and νb around 500 cm−1, the linewidth Гa of the strongest νa peak, and the wavenumber difference Δcb between νc and νb peaks, where νc is a Raman feature at ~560–580 cm−1. The calibration was completed from data sets composed of spectra from metamorphic to pegmatitic plagioclase. The results were then tested against a further data set, mostly made by volcanic plagioclase. In most samples, the difference between electron micro probe analysis (EMPA) and Raman compositions is less than 5%. Higher residuals (beyond 10%) are observed for intermediate plagioclase, suggesting that some differences in Δab exist between volcanic and metamorphic plagioclase of intermediate compositions. The Raman compositional results for a plagioclase from Marsili submarine volcano agree with composition and zoning found from the analysis by laser ablation.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA74
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
08 - Green Open Access
Journal or Publication Title: Journal of Raman Spectroscopy
Identification Number: https://doi.org/10.1002/jrs.5340
Depositing User: Sarah Humbert
Date Deposited: 08 Mar 2018 22:58
Last Modified: 08 Mar 2018 22:58
URI: http://eprints.esc.cam.ac.uk/id/eprint/4125

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