Volatile contents, degassing behaviour and hydration of early-erupted rhyolitic pyroclasts and ashes from Vulcan Chaitén, Chile

The concentration of dissolved volatile species in silicic pyroclasts, especially that of water, can yield key information about magma degassing and fragmentation depths. However, post-eruptive hydration can be highly problematic, with meteoric water overprinting magmatic water contents, especially in fine-grained or highly porous samples that have large surface area to volume ratios. In this study we have used thermogravimetric analysis-mass spectroscopy (TGA-MS) to characterize the volatile contents and degassing behaviour of a selection of juvenile pyroclasts and ashes erupted from Chaitén volcano, Chile in May-June 2008. The advantage of the selected samples is the short delay between eruption and collection (days to weeks), meaning that post-eruptive hydration ought to be minimal. The samples analysed, which were collected from proximal fallout deposits in June 2008, include a suite of centimetric pumices and obsidian clasts of varying porosity, the