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Foaming, shearing and outgassing in obsidians during 4D vesiculation experiments

Mathieu Colombier 1, Francisco Cáceres1,2, Janine Birnbaum1, Rebecca deGraffenried3, Bettina Scheu1, Simon Thivet1,4, Pedro Valdivia5, Ruben M. Ruhekenya1,6, Christian Schlepütz7, Kai-Uwe Hess1, Donald B. Dingwell1

  • Affiliations: 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany; 2Facultad de Ciencias Básicas, Universidad Católica del Maule, Talca, Chile; 3Geological Sciences, University of Missouri, Columbia, USA; 4 Department of Earth Sciences, University of Geneva, Geneva, Switzerland; 5Bavarian Research Institute of Experimental Geochemistry and Geophysics, Universität Bayreuth, Bayreuth, Germany; 6Vrije Universiteit Amsterdam, Amsterdam, Netherlands; 7Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 226

  • Programme No: 3.17.13

  • Theme 3 > Session 17

Abstract

Vesiculation in silicic magmas controls the release of gas to the atmosphere, as well as the eruptive style of silicic volcanoes, and is often accompanied by pure or simple shear deformation. Deformation is commonly localized at the micro-scale, as revealed by the pervasive textural evidence for strain localization in explosive and effusive products. Micrometric shear bands with highly stretched and sheared vesicles can alternate with bands with more isotropic vesicles. The evolution of bubble deformation in these bands is important because: (i) deformation can reduce the percolation threshold (the transition between closed- and open-system degassing), decrease tortuosity and increase anisotropy in magma; the contribution of these processes favouring permeable gas escape; (ii) bubble deformation can be used as a strain and stress marker and hence an indicator of the stress and strain conditions extant at fragmentation; (iii) deformation can enhance rheological heterogeneities. All these consequences can influence the explosive/effusive behaviour of magma in the shallow conduit. In this study, we monitor the development and evolution of shear bands at the microscale in silicic magma using 4D synchrotron-based foaming experiments on obsidian from Lipari volcano (Italy). We measure bubble characteristics during heating-induced vesiculation, including the evolution of vesicularity, vesicle size distribution, vesicle shape and orientation, and development of permeability. Numerical simulations of pressure and velocity (linearized Navier-Stokes) and diffusive bubble growth highlight the complex feedbacks between bubble growth, pressure, shear, and outgassing. The implications for the competition between outgassing and expansion in volcanic conduits at different scales are discussed.