 |
| Titel |
Fluid inclusions and microstructures in experimentally deformed quartz single crystals |
| VerfasserIn |
A. Thust, A. Tarantola, Renée Heilbronner, H. Stünitz |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022243
|
|
|
|
|
|
| Zusammenfassung |
| The “H2O-weakening” effect that reduces the strength of quartz dramatically (e.g. Griggs &
Blacic 1965) is still not understood. For example, Kronenberg & Tullis (1984)
conclude that the weakening effect is pressure dependent while Paterson (1989)
infers a glide and recovery control of water. Obviously, the spatial distribution and
transport of H2O are important factors (Kronenberg et al. 1986, FitzGerald et al.
1991).
We have carried out experiments on milky quartz in a Griggs deformation apparatus.
Cylinders (6.5 mm in diameter, 12-13 mm in length) from a milky zone of a natural quartz
single crystal have been cored in orientations (1) normal to one of the prism planes and (2)
45˚ to and 45˚ to (O+orientation).
At 1 GPa confining pressure, 900˚ C and 10-6s-1, the flow strength is 150 MPa for
samples with orientation (1). Further experiments are needed to establish the flow strength for
orientation (2).
FTIR measurements on double-polished thick sections (200-500 μm) in the undeformed
quartz material yield an average H2O content of approximately 100 H/106Si. The water is
heterogeneously distributed in the sample. Direct measurements on fluid inclusions yield
a H2O content of more than 25 000 H/106Si. Thus, the H2O in the undeformed
material is predominantly present in fluid inclusions of size from tens to hundred
microns.
Micro-thermometric measurements at low temperature indicate the presence of different
salts in the fluid inclusions. The ice melting temperature, between -6.9 and -7.4˚ C, indicate
an average salinity of 10.5 wt% NaCl.
After deformation the distribution of H2O is more homogeneous throughout the sample.
The majority of the big inclusions have disappeared and very small inclusions of several
microns to sub-micron size have formed. FTIR measurements in zones of undulatory
extinction and shear bands show an average H2O content of approximately 3000 H/106Si.
Moreover, the larger fluid inclusions are characterized by a higher salinity (12 wt%) due to
H2O loss into the healed cracks.
First observations of deformed samples show abundant deformation lamellae. With higher
deformation the lamellae form conjugated zones of high dislocation density and
undulatory extinction. Micro cracks are frequently connected to fluid inclusions.
Recrystallized grains are rare in deformed samples because of the low strain acquired. In
semi-brittle experiments at lower temperature and faster strain rates considerable
recrystallization features are visible and clearly connected to initial brittle deformation
features.
We conclude that fluid inclusion rupture and fast crack healing at high temperatures are
necessary for the redistribution of H2O and a prerequisite of ductile deformation.
References:
Griggs, D.T. & Balcic, J.D. 1965: Quartz: anomalous weakness of synthetic crystals.
Science 147, 293-295.
FitzGerald, J.D., Boland, J.N., McLaren, A.C., Ord, A., Hobbs, B.E. 1991:
Microstructures in water-weakened single crystals of quartz. Journal of Geophysical
Research Vol. 96 No. B2, 2139-2155
Kronenberg, A.K. & Tullis, J. 1984: Flow strength of quartz aggregates: grain size and
pressure effects due to hydrolytic weakening. Journal of Geophysical Research Vol.89, No.
B6, 4281-4297.
Kronenberg, A.K., Kirby, S.H., Aines, R.D., Rossman G.R. 1986: Solubility and
diffusional uptake of hydrogen in quartz at high water pressures: implication for hydrolytic
weakening. Journal of Geophysical Research Vol.91, NO. B12, 12,723-12,744.
Paterson, M.S.1989: The interaction of water with quartz and the influence in dislocation
flow – an overview. In: S. Karato and M. Toriumi (Editors), Rheology of Solids and of the
Earth. Oxford University Press, London, pp. 107-142. |
|
|
|
|
|
|