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Soutenance de thèse de Swetha Venugopal

18 October 2019 à 18 h 00 min - 20 h 00 min

Swetha Venugopal soutiendra sa thèse le vendredi 18
octobre à 9h (heure locale de Vancouver ; 18h à Clermont) dans la salle
n°2020 à la bibliothèque de l’Université Simon Fraser (Vancouver, Canada).

Vous trouverez
ci-dessous le titre et le résumé de la thèse.

Titre : From magmatic sources to volcanic gas emissions: insight from the
Garibaldi Volcanic Belt, western Canada


Director: Tim Druitt (UCA)
Directrice: Severine Moune (UCA)
Director: Glyn Williams-Jones (SFU)

Examinatrice: Gwenn Flowers (SFU)
Examinatrice: Nathalie Vigouroux-Callibiot (Douglas College)

Rapporteur: Brendan Dyck (SFU)
Rapporteur: Jacob Lowenstern (USGS)


Volcanoes are the surficial representation of the complex interplay of
magmatic, crustal, and hydrothermal processes operating below the Earth’s
surface. Studying volcanic deposits provides a unique snapshot into the
composition of the deep mantle source. Melt inclusions, which are small
pockets of magma trapped inside growing crystals, preserve multi-faceted
records of magma petrogenesis. Additionally, the magma at depth contains a
significant proportion of dissolved magmatic gases. Once these gases
become saturated in the magma, they exsolve into a separate vapour phase
and ascend quickly to the surface, where they are released as volcanic
gases. The composition of gases at the surface can provide valuable
insight into the composition of the magma at depth, as well as the
shallow-level hydrothermal system. Volcanic gases are an important factor
controlling whether an eruption is gentle and effusive, or violent and
explosive. A greater amount of gas that separates at depth can trigger
large, explosive eruptions (Devine et al., 1998; Shinohara, 2008).
Therefore, gas detection at the surface is an essential monitoring tool
for eruption forecasting. In this thesis, I begin with an in-depth look
inside glassy and crystallized olivine-hosted melt inclusions and assess
the nature of micron-scale solid phases occupying the vapour bubble. From
here, major, volatile and trace element compositions of olivine-hosted
melt inclusions from every centre along the Garibaldi Volcanic Belt (GVB)
reveals a north to south transition from an enriched mantle signature, to
a subduction-modified depleted mantle source. Finally, the recent
re-discovery of fumaroles beneath the summit glacier of Mount Meager has
prompted the first MultiGAS survey in the GVB. The plumes are H2S, CO2 and
H2O rich, and hot enough to melt through the overlying ice. Can the
basaltic magma, represented by melt inclusions, produce the volcanic gases
currently emitted at the surface? To test this, two different gas
modelling software (SolEx and MagmaSat) are used, along with original and
recalculated (with the bubble components) as input parameters. The
resulting molar ratios are compared with MultiGAS ratios of fumaroles.
Overall, SolEx closed-system degassing using recalculated melt inclusions
yields the best approximation to MultiGAS ratios. This thesis addresses a
compositional knowledge gap within the GVB. By understanding both the
distinct magmatic sources underlying the arc, as well as the composition
of volcanic gases emanating from summit fumaroles, we gain a broad and
comprehensive geochemical overview of the Garibaldi Volcanic Belt.

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18 October 2019
18 h 00 min - 20 h 00 min