Using Experimental Techniques The Study of Melt Dynamics in Samples under both Deformation and Static Conditions
During my internship at the University of Minnesota in the summer of 2004 I worked in Professor David Kohlstedt's experimental geophysics laboratory. My research project included a series of experiments in which I deformed synthetic samples of upper mantle rock at high temperature and pressure (1250 C, 300 MPa - confining pressure) in a Paterson aparatus. The composition of these samples were, in weight percent: 76% Olivine + 20% Chromite + 4% mid ocean ridge basalt (MORB). At the deformation conditions given above, the MORB is a fluid, while the other species are solids. The study of melt dynamics in samples under both deformation and static conditions was the broad goal of my research.
Previous work by Dr. Ben Holtzman shows that melt-rich bands can form
in samples sheared at high T and P. Our experiments build on those
done previously by Holtzman in order to produce melt bands in our samples.
After the samples were sheared, they were statically annealed at high temperature
and pressure to determine how the melt bands would change. The results
from these experiments indicate that melt bands are not stable under static
conditions due to the removal of the pressure gradients driving melt segregation
that are present under deformation conditions. During the annealing
process diffusional mechanisms tend to redistribute melt back into melt
depleted regions of the sample. These results imply that regions
of the upper mantle in which melt is concentrated (mid ocean ridges, hot
spots e.g.) are also regions where the mantle is being deformed - promoting
the segregation of melt into channels.