Microlite orientation in obsidian flow measured by synchrotron X-ray diffraction
- Author(s): Manga, M
- Voltolini, M
- Wenk, HR
- et al.
Published Web Locationhttps://doi.org/10.1007/s00410-018-1479-9
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  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.