Rev. Mineral. Geochem. 69. 61-120

Improving our understanding of magma plumbing and storage remains one of the major challenges for petrologists and volcanologists today. This is especially true for explosive volcanoes, where constraints on magma plumbing are essential for predicting dynamic changes in future activity and thus for hazard mitigation. This study aims to investigate the magma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the 1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rate of ∼8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometr

Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain

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