FTIR Spectrum of Phenocryst Olivine as an Indicator of Silica Saturation in Magmas.

Matveev, S., Portnyagin, Maxim V., Ballhaus, C., Brooker, R. and Geiger, Charles (2005) FTIR Spectrum of Phenocryst Olivine as an Indicator of Silica Saturation in Magmas. Journal of Petrology, 46 (3). pp. 603-614. DOI 10.1093/petrology/egh090.

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Fourier Transform infrared (FTIR) absorption spectra of hydroxyl were measured on olivine phenocrysts from hydrous basaltic melts that originated in island-arc tectonic settings. The basaltic melts encompass a wide range of silica activities from orthopyroxene-saturated hypersthene-normative to nepheline-normative compositions. The intensities and wavenumber placement of hydroxyl absorption bands correlate with the degree of silica saturation of the parent melt from which the olivine crystallized. Olivines from silica-undersaturated nepheline-normative melts absorb IR radiation in the wavenumber range 3430-3590 cm(-1) (Group 1). In contrast, olivines from orthopyroxene-saturated boninitic melts exhibit hydroxyl absorption bands in the wavenumber range 3285-3380 cm(-1) (Group 2). Olivines crystallized at intermediate silica activities exhibit a combination of the two groups of hydroxyl IR bands, where the proportion of Group 2 bands increases with increasing silica saturation of the parent melt. The positions of hydroxyl absorption peaks observed here for natural samples are consistent with previous measurements on experimentally annealed olivines. Thus protonation experiments can be employed to make spectroscopically dry olivine structures visible by IR, yielding information on the silica saturation of the parental magmas. Hydroxyl concentrations in the studied olivines were estimated to be 1-2 ppm, corresponding to an olivine-melt partition coefficient of similar to(1.0 +/- 0.3) x 10(-4).

Document Type: Article
Keywords: nominally anhydrous minerals; olivine; water; mantle; silica activity; melt inclusions
Research affiliation: Kiel University
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1093/petrology/egh090
ISSN: 0022-3530
Projects: KOMEX II
Date Deposited: 03 Dec 2008 16:50
Last Modified: 14 Nov 2017 10:03
URI: http://oceanrep.geomar.de/id/eprint/6336

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