EPS Colloquium: Glenn Gaetani
Magma Storate and Ascent Beneath the Erebus Volcanic Province, Antarctica: Insights from Olivine-Hosted Melt Inclusions
The depths at which magmas are stored, their pre-eruptive volatile contents, and the rates at which they ascend are interrelated, and exert important controls on the dynamics of volcanic eruptions. Olivine-hosted melt inclusions from the Erebus volcanic province of Antarctica provide an opportunity to investigate these interrelationships. Most volcanism occurs in the Ross Island and Discovery sub-provinces, each comprised of a central stratovolcano surrounded by three radially distributed eruptive complexes. Melt inclusions preserve information relating to magma storage and transport beneath these volcanos. The concentrations of water and carbon dioxide reflect the depths of entrapment. Magma degassing during ascent drives diffusive water loss from melt inclusions. Preferential loss of hydrogen (H) – relative to the more slowly diffusing deuterium (D) – produces increasing D/H with decreasing water concentration in the melt inclusions. The extent of diffusive water loss and D/H fractionation reflect ascent time and the nature of degassing (open versus closed system). Entrapment pressures indicate a magma reservoir at ~24 km – in agreement with the seismically determined Moho beneath Ross Island. Results from diffusion modeling indicate closed system degassing and an average ascent rate of ~0.5 – 2.0 m/s. This gives a transit time from the Moho of only ~3-13 hours.