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Microlite orientation in obsidian flow measured by synchrotron X-ray diffraction

  • Author(s): Manga, Michael
  • Voltolini, Marco
  • Wenk, Hans-Rudolf
  • et al.
Abstract

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Clinopyroxene and plagioclase (andesine) microlites in an obsidian flow from Glass Mountain (NE California, USA) display strong alignment. Synchrotron X-ray diffraction, coupled with Rietveld analysis, was used to quantify crystallographic-preferred orientation (CPO). Clinopyroxene, with a rod-shaped morphology, shows a strong alignment of [001] in the flow direction and (010) aligned parallel to the inferred flow plane. Andesine, with a platy morphology, displays an alignment of (010) platelets in the flow plane. Some pole densities exceed 90 multiples of random distribution. Applying a model of rigid ellipsoidal inclusions in a viscous matrix, the local pure shear strains are between 2 and 3.

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