5th Swiss Geoscience Meeting, Geneva 2007
Experimental Deformation on natural quartz single
crystals
Thust Anja*, Heilbronner Renée**, Stünitz Holger***
Department of Environmental Sciences, Geological Institute Bernoullistr. 32
CH-4056 Basel Switzerland
(*anja.thust@unibas.ch, **renee.heilbronner@unibas.ch,
***holger.stuenitz@unibas.ch)
Quartz – one of the most common minerals in the earth's crust – is well studied
in nature and in experiments. A lot of experimental studies were carried out
using synthetic quartz and polycrystalline material. Still, one poorly understood
issue is the influence of the water content and its influence of the rheological
behavior. Furthermore, there is no experimental data of natural quartz material
showing the temperature dependence of slip system activity.
In this project we will investigate the 3 main slip systems of natural quartz in
single crystals at different temperatures and the effect of water on their
activation. The experiments will be carried out in a solid medium Griggs
apparatus.
Different sample materials and sample geometries are presently being tested in
our laboratory. The quartz single crystals should be milky and should not
contain microcracks. Unlike Vernnoij et al. (2006), who have recently performed
single crystal experiments on dry quartz, we intend to use wet (milky) quartz
and add no water. The goal is to deform the crystals without cracking in order to
look at the activation and resolved shear stresses of different slip systems.
For the first series of experiments we use an orientation perpendicular to (m)
and [c] and another orientation 45° to the basal plane and down a. Later we
will use other orientations and extend the study to bi-crystals.
The first experiments were performed at confining pressures of 10 to15 kb and
at a temperature of 900°. They are deformed in uniaxial compression at
constant displacement rates and at constant stress.
One of the initial problems is to attain the experimental conditions without
developing microcracks during the pressure increase. We have developed
several techniques to minimize the cracking by modifying the sample assembly.
Some of our samples clearly show plasticity – dominated microstructures.
REFERENCES:
Vernooij, M.G.C., Kunze, K., den Brok, D. 2006: Brittle shear zones in
experimentally deformed quartz single crystals. Journal of Structural Geology
28, 1292-1306.