Date/Time
Date(s) - Thu 28 September
16:00 - 17:00
Location
CO304, Cotton Building, VUW
Efficient outgassing of magmatic volatiles is key to diffusing explosive eruptive behaviour. The existence of degassed lavas in the geological record confirms this can occur during rhyolitic eruptions, but degassing mechanisms have remained enigmatic due to the lack of observed activity. Recent eruptions at Chaitén (2008-09) and Cordón Caulle (2011-12) in Chile offer unprecedented opportunities to better constrain how rhyolitic magma degasses. Simultaneous lava effusion and vulcanian explosions were observed; hybrid activity that requires a new paradigm to explain behavioural transitions during high-silicic eruptions. Particle-filled fracture networks (tuffisite veins) have been preserved in aphyric bombs from the hybrid phases of both eruptions. It is proposed that fractures provide transient gas escape pathways, with textures recording multi-stage degassing within the shallow volcanic conduit. The major volatile components of exsolved magmatic vapour (H2O, CO2, S, Cl, F) act as ligands or carrier gases for low concentration, volatile trace elements (e.g. Pb, Tl, Cu, Rn, Hg) that are enriched in plumes and fumaroles. We assess the efficiency of vein networks as outgassing pathways in rhyolites using trace-element and isotope variations associated with these features.
All Welcome