Lab 1c-Deformation Mechanisms
VIEPS/Mainz Microstructure Course
| TOC | Lecture 1
2 3
4 a b
5 a b
| Lab 1 a b
c 2 a
b c 3
a b 4
a b 5
a b |
Glossary Table 1
2 3
4 5
Index |
3) Evidence of crystalline plasticity in naturally deformed
rocks.
These micrographs display a variety of deformation microstructures,
for this practical only worry about those which reflect deformation by
crystalline plasticity.
a) Quartzite Weak to moderate deformation of a quartzite with
minor micas at low metamorphic grade. Original clastic quartz grains show
numerous features of intra-crystalline plasticity, including deformation
bands, and undulose extinction.
The figure below shows a quartz grain with the
trace of the basal plane. Using a stippled pen, show what this grain would
look like (ie its extinction characteristics) in crossed polarised light,
assuming the polarisers are parallel to the cross.
Now look at grain A in the top right hand corner,
and make a sketch of its basal plane (assuming the dark bands are sub-perpendicular
to the basal plane, as they usually are in low temperature deformed quartz).
b) Marble A typical low grade deformed
marble, showing extensive twinning.
The quartz grains embedded in the middle of the calcite
appear to be relatively undeformed, why?
Why are the twin planes in the calcite curved?
c) Mt Kosciusko Granite
The quartz and feldspar in this granite appear to
have deformed by quite distinct deformation mechanisms, why?
Place a cross on the generic deformation mechanism
map below for both the quartz and the feldspar. On the same diagram show
the calcite from the previous picture as an arrow showing its history.
The quartz grains have undergone at least a 10x reduction
in grain size, how might this affect the mechanical response of the quartz?