Hydroxyl speciation in felsic magmas

Wim J. Malfait, Xianyu Xue

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27Al-1H cross polarization and quantitative 1H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1H NMR partial spectrum was derived from the 27Al-1H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si-O-Si, Si-O-Al and Al-O-Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al-O-Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84-89% and 68-78%, respectively), but with a significant fraction of Al-OH (11-16% and 22-32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH+SiOH) ratio is likely smaller than the Al/(Al+Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al+Si) ratio at higher temperatures.

Original languageEnglish
Pages (from-to)606-620
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume140
DOIs
Publication statusPublished - Sep 1 2014

Fingerprint

aluminosilicate
Hydroxyl Radical
glass
Glass
Potassium
potassium
calcium
nuclear magnetic resonance
Aluminum
polarization
aluminum
Sodium
Nuclear magnetic resonance
sodium
Polarization
MAS
Spectral resolution
lithium
spectral resolution
Lithium

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Hydroxyl speciation in felsic magmas. / Malfait, Wim J.; Xue, Xianyu.

In: Geochimica et Cosmochimica Acta, Vol. 140, 01.09.2014, p. 606-620.

Research output: Contribution to journalArticle

Malfait, Wim J. ; Xue, Xianyu. / Hydroxyl speciation in felsic magmas. In: Geochimica et Cosmochimica Acta. 2014 ; Vol. 140. pp. 606-620.
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