Strain-induced outgassing of three-phase magmas during simple shear

J. K. Shields*, H. M. Mader, M. Pistone, L. Caricchi, D. Floess, B. Putlitz

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

31 Citations (Scopus)
44 Downloads (Pure)

Abstract

A major factor determining the explosivity of silicic eruptions is the removal of volatiles from magma through permeability-controlled outgassing. We studied the microstructural development of permeability during deformation of highly viscous magma by performing simple shear experiments on bubble (0.12-0.36 volume fraction) and crystal-bearing (0-0.42 volume fraction) silicate melts. Experiments were performed under torsion, at high temperature and pressure (723-873 K and 150-200 MPa) in a Paterson deformation apparatus at bulk shear strains between 0 and 10. The experimental setup allows for gas escape if bubble connectivity is reached on the sample periphery. Three-dimensional imaging and analysis of deformed bubbles was performed using X-ray tomography. The development of localized deformation in all samples, enhanced by crystal content, leads to brittle fracture at bulk strains > 2 and sample-wide fracturing in samples deformed to strains >5. A decrease in both bubble fraction and dissolved volatile content with increasing strain, along with strain-hardening rheological behavior, suggests significant shear-induced outgassing through the fracture networks, applicable to shallow conduit degassing in magmas containing crystal fractions of 0-0.42. This study contributes to our understanding of highly viscous magma outgassing and processes governing the effusive-explosive transition.

Original languageEnglish
Pages (from-to)6936-6957
Number of pages22
JournalJournal of Geophysical Research: Solid Earth
Volume119
Issue number9
DOIs
Publication statusPublished - Sep 2014

Keywords

  • shear experiments
  • three-phase magmas
  • bubbles
  • localization
  • outgassing
  • obsidian
  • DOME-BUILDING ERUPTIONS
  • NON-NEWTONIAN RHEOLOGY
  • MOUNT ST-HELENS
  • SILICIC VOLCANISM
  • RHYOLITIC MELTS
  • ASCENT DYNAMICS
  • FLOW
  • DEFORMATION
  • PERMEABILITY
  • GLASSES

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