ABSTRACT
Microstructural development in a rock analog crystal-melt system
is focused on in this study, using an experimental technique in
which microstructurel changes can be observed in situ and
processes can be inferred from the microstructurel changes. The
aim of the work has been to contribute to the basis for
understanding the origin and significance of textural features of
rocks that have passed through a melt-present interval in their
history.
During isothermal deformation experiments, microstructures
indicating crystal plasticity and dynamic recrystallization are
observed at fast strain rates. At slow strain rates, a pressure
solution-like process, contact melting/redeposition, is active,
resulting in optically strain-free crystals. Grain boundary
sliding is also active during slow strain rate deformation, with
concurrent accommodation process of contact melting/redeposition
and assisting process of grain boundary migration.
Textural metamorphism such as dendrite segmentation and
coarsening, and grain and phase boundary migration is observed to
start in the analog system even at supersolidus conditions.
Stimulated by observations of coarsening in the analog system,
some physical and numerical experiments were carried out to
discover the rates of coarsening in silicate crystal-melt systems.
Results from experiment and simulation suggest that the kinetics
of forsterite coarsening is fast enough to remove small crystals
in a short period of time compared to the time required for
complete solidification of a magma. These processes may introduce
complications when attempting to infer the rates of processes in
rocks such as crystal growth and nucleation, and the order of
crystallization.
The validity of this type of analog experiment is checked using
scale modelling. It is found that non-steady state structures in
the experiment can be identical to that in the natural system only
when the experimental relative rates of processes at an instant
are identical to those in the natural system. Given these
complications, the experimental results from the analog system may
not have any parallels in natural conditions. However, this type
of experiment, even if unscaled, can provide some building blocks
for the later more thorough models which can better link processes
and microstructural changes.
Park, Y., 1994. Microstructural evolution in crystal-melt
systems.
Unpublished PhD dissertation, State University of New York at
Albany. 385pp., +xiv
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1994 P37
Copies of this PhD dissertation can be ordered
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Front matter (title,
table of contents, abstract, acknowledgements) - 0.4MB pdf
file
Figure pages in dissertation
(all
figures and photos with captions): -28.6MB pdf file
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