Rapid reequilibration of H2O and oxygen fugacity in olivine-hosted melt inclusions

Abstract

DefinitionsD VSMOW is the difference between the measured D/H ratio of a sample and the D/H ratio of Vienna Standard Mean Ocean Water (VSMOW) expressed in per mil (‰):

Volatile (F and Cl) concentrations in Iwate olivine-hosted melt inclusions indicating low-temperature subduction

“…Magmatic degassing H 2 O concentrations measured in Iwate melt inclusions are at best considered as minimum water concentrations because melt inclusions are leaky containers for H 2 O (Chen et al 2011(Chen et al , 2012Gaetani et al 2012). An indication of water loss in Iwate melt inclusions is the weak anti-correlation between H 2 O and TiO 2 .…”

“…However, a note of caution is sounded because melt inclusions are leaky containers for H 2 O (Chen et al 2011;Gaetani et al 2012). CO 2 solubility in silicate melt is significantly lower than that of H 2 O and therefore CO 2 degassing begins earlier during magma ascent, i.e.…”

Contrasting partition behavior of F and Cl during hydrous mantle melting: implications for Cl/F signature in arc magmas

“…Moreover, olivine-hosted melt inclusion studies have shown that F and Cl, unlike H 2 O, are less affected by post-entrapment diffusion through the host mineral (e.g. Gaetani et al 2012;Bucholz et al 2013;Lloyd et al 2013;Le Voyer et al 2014). Therefore, the F and Cl contents recorded by arc melt inclusions represent the product of fractional crystallization from primary melts, and thus they retain valuable information on the source composition of arc magmas.…”

Discussion on ‘Magma storage region processes of the Soufrière Hills Volcano, Montserrat’, Geological Society, London, Memoirs , 39, 361-381

“…This is the reason that we excluded these samples from our study of H 2 O and Cl degassing (Humphreys et al 2009b). By comparison with the well-documented similar effect in both natural and experimental olivines (Hauri 2002;Portnyagin et al 2008;Gaetani et al 2012) we infer that water loss may result from diffusion of H through the host phenocryst, as demonstrated experimentally by Johnson & Rossman (2013). The extent of diffusive loss probably depends on clast size (Lloyd et al 2013) as well as the permeability of the dome, and probably occurs during prolonged storage at low pressures (perhaps in the lava dome itself) and at, or close to, magmatic temperatures.…”

“…If this is the case, we would also expect these inclusions to have anomalously oxidizing compositions (e.g. Gaetani et al 2012;Humphreys et al in press). …”