Petrological insights into pre- and syn-eruptive degassing at Ambrym volcano, Vanuatu

Sheehan, Fionnuala (2016) Petrological insights into pre- and syn-eruptive degassing at Ambrym volcano, Vanuatu. Doctoral thesis, University of East Anglia.

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This study is a petrological investigation of magmatic conditions and degassing
processes at Ambrym volcano, a basaltic island arc volcano recently identified as a prodigious
emitter of volcanic gases. Typical activity at this volcano entails heavy degassing from quasipermanent
lava lakes, with Strombolian activity of fluctuating intensity. This is punctuated on
an approximately decadal timescale by moderate sub-Plinian paroxysms, often accompanied
by overflow of lava from the intracaldera cones and via flank fissures.
This study focuses primarily on basaltic scoria recently erupted from a central lava lake
during a period of heavy degassing, in order to interpret volatile pathways through the system
and how these relate to gas emissions at the surface. Lavas from basaltic intracaldera and
flank lava flows have also been briefly examined to give a broader insight into magma storage
associated with variations in volcanic activity, and detailed study has been made of a
trachyandesitic lava flow erupted in 1986, a geochemically unusual event compared to the
majority of larger events in historical time.
Petrography, major element modelling, mineral chemistry and dissolved volatile contents
indicate that Ambrym is a water-poor, CO2-rich system, characterised chiefly by quiescent
convection-driven degassing through two central intracaldera cones. Examination of the 1986
trachyandesite suggests that it derives from interaction of basaltic magma with a body of
trachydacitic melt residing in the shallow crust.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 7376 not found.
Date Deposited: 17 Jun 2016 13:17
Last Modified: 17 Jun 2016 13:17


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