Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain
2015 (English)In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 7, 2127-2146 p.Article in journal (Refereed) Published
Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles,because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. Theparental water content of a magma is usually measured through melt inclusions in minerals such as olivine, amethod which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapmentchanges in their water content. An alternative way to reconstruct the water content of a magma is touse nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogenas a function of the magma’s water content. During magma degassing and eruption, however, NAMs maydehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrystsfrom the Western Canary islands (n=28) through rehydration experiments followed by infrared andM€ossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experimentswere used to calculate parental water contents of 0.71±0.07 to 1.49±0.15 wt % H2O for WesternCanary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreementwith calculated water contents using plagioclase-liquid-hygrometry, and with previously published datafor mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs incombination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which weanticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.
Place, publisher, year, edition, pages
2015. Vol. 16, no 7, 2127-2146 p.
Geosciences, Multidisciplinary Geology
Research subject The changing Earth
IdentifiersURN: urn:nbn:se:nrm:diva-1440DOI: 10.1002/2015GC005800OAI: oai:DiVA.org:nrm-1440DiVA: diva2:875652