Abstract:
The shape and three-dimensional orientation distribution
of microlites are measured in obsidian from Little Glass Mountain,
California.
Measurements are made from thin sections
using an image series
of high magnification
digital micrographs taken serially through
different focal depths.
These measurements agree well with the
theoretically predicted and experimentally measured
distribution of long slender rods in a
Newtonian fluid undergoing simple
shear flow. In this type of flow, rods in a dilute
suspension rotate periodically,
spending most of the time aligned with the flow.
Measurements of the detailed orientation distribution
integrated with theoretical models provide a tool for inferring
flow dynamics and the timing of magmatic processes.