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Earth and Planetary Science Letters 306, 3-4 (2011) 261-271
Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica
Clive Oppenheimer 1, 2, Roberto Moretti 3, 4, Philip R. Kyle 5, Al Eschenbacher 5, Jacob B. Lowenstern 6, Richard L. Hervig 7, Nelia W. Dunbar 8

Continental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4 kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer).
1 :  University of Cambridge (UK) (CAM)
University of Cambridge (UK)
2 :  Institut des Sciences de la Terre d'Orléans (ISTO)
CNRS : UMR6113 – INSU – Université d'Orléans – Université François Rabelais - Tours
3 :  INGV-Napoli
Osservatorio Vesuviano
4 :  Centro Interdipartimentale di Ricerca in Ingegneria Ambientale (CIRIAM)
Seconda Università degli studi di Napoli
5 :  New Mexico Institute of Mining and Technology
New Mexico Institute of Mining and Technology
6 :  Volcano Hazards Team
U.S. Geological Survey
7 :  School of Earth and Space Exploration
Arizona State University
8 :  New Mexico Institute of Mining and Techonoloy
New Mexico Institute of Mining and Techonoloy
Planète et Univers/Sciences de la Terre/Volcanologie

Sciences de l'environnement/Milieux et Changements globaux
CO2 fluxing – degassing – Strombolian eruptions – lava lake – melt inclusions – redox
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Oppenheimer-EPSL-2011.pdf(892.1 KB)