Skip to content

Quantifying magma deformation conditions from crystal-plasticity

Jackie E. Kendrick1; Paul A. Wallace1; Takahiro Miwa2; Yan Lavallée1

  • Affiliations: 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany; 2National Research Institute for Earth Science and Disaster Resilience, Ibaraki, Japan

  • Presentation type: Poster

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

  • Poster Board Number: 221

  • Programme No: 1.9.28

  • Theme 1 > Session 9

Abstract

The evolution of multiphase magmas during shear remains a critical question in volcanology. The presence of solid, liquid, and gaseous phases partitions strain, and in suspensions with high interstitial melt viscosity, high crystal content, or low vesicularity, large stresses may accumulate in the crystalline phase, which may result in crystal plasticity and rupture. EBSD mapping of experimentally deformed, porous, crystal-rich dome lavas (at magmatic temperature) revealed that plagioclase (which dominated the crystal assemblage) underwent dislocation creep. The misorientation of the crystal lattices increased as a function of stress and strain, until rupture. Grain size reduction was seen synchronous to deformation, and fragments of broken microlites recorded the highest distortions; thus, crystals exhibit a plastic limit during dislocation creep. The systematic variation in plasticity with applied conditions demonstrates the key role of crystal plasticity in the deformation of crystal-rich lavas, and the possibility to interpret deformation from the imparted dislocations. To test this, we mapped crystal-plasticity in the lava spine erupted at Unzen in 1994−1995 and found that the degree of crystal lattice misorientation in plagioclase microlites increased systematically across the shear zone towards the marginal shear plane. This work demonstrates how crystal plasticity can map strain localisation textures formed during magma deformation, and although to date insufficient data exists to define the stress--strain history of magmas from the vestiges of crystal-plasticity, there remains hope for its use as a strain marker in the future, with further systematic quantification.