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The milky appearance of the quartz crystal originates from a large number of fluid inclusions. Fluid inclusions on the undeformed
material are arranged on planes more or less perpendicular to c . They showed a high variation in size and
shape with negative-crystal to undefined morphologies.
Microthermometric measurements at low temperature revealed the presence of antarticite (CaCl 2 ·6H 2 O) and hydrohalite
(NaCl·2H 2 O). Ice melting temperature ranged between -6.9 and -7.4 °C, corresponding to an average salinity of 10.5 wt% eq.
NaCl. Total homogenization temperatures were measured between 184 °C and 207 °C. Raman microspectroscopy permitted
to observe the presence of small amounts of CO 2 and to identify some accidentally trapped solids in the inclusions like calcite,
quartz or rutile. The molar volume of the inclusions helped us to determine the fluid pressure as a function of the
temperature. At 250 °C, the fluid pressure is around 100 MPa and in the order of 850 MPa at 700 °C.
FTIR measurements on double-polished thick sections (200 to 500 µm) present an average H 2 O content of 250 H/10 -6 Si in undeformed
samples (calculation after Stipp et al. 2006). The H 2 O –content is heterogeneously distributed. The undeformed
quartz material shows a fluid inclusions with variable size, up to 0.5 mm. FTIR measurements on inclusions often have
oversaturated absorption spectrums. Next to the fluid inclusions there are can be clear regions without any inclusions and
essentially no H 2 O. After deformation the H 2 O distribution is more homogenous throughout the sample. The majority of the
big inclusions have disappeared and a lot of small inclusions are formed and are often arranged in fluid clusters. The H 2 Ocontent
of deformed regions with undulatory extinction is approximately 3000 H/10 -6 Si. Thus, H 2 O becomes dispersed during
deformation. We infer that during deformation the inclusions disrupt and form micro cracks. The cracks heal rapidly at the
high temperatures and confining pressures. During the healing and plastic deformation H 2 O is distributed in the quartz
crystals via defects and contributes to the H 2 O-weakening effect.
One interesting feature in the FTIR absorption spectrum of the deformed samples is a sharp, small peak at 3595 cm -1 . This
peak appears only in the deformed samples and there only in the visibly deformed parts (see figure1).
The sharp FTIR peak seems to be linked to the deformation. Niimi et al. 1999 consider that this peak is related to recrystallization,
but in our case is no evidence for recrystallization could found.
In conclusion we can say that quartz which shows a low H 2 O distribution and a lot of fluid inclusions provides enough H 2 O
for H 2 O weakening. The inclusions changes their shape, their size, their composition and the H 2 O dispersion becomes more
homogeneous during deformation by microcracking and subsequent crystal plastic deformation by dislocation glide.
REFERENCES:
Griggs, D.T. & Balcic, J.D. 1965: Quartz: Anomalous Weakness of Synthetic Crystals. Science 147, 293-295.
Hirth, G. & Tullis, J. 1992: Dislocaton creep regimes in quartz aggregates. Journal of Structural Geology. 14, 145-159.
Niimi, N., Aikawa, A., Shinoda, K. 1999: The infrared absorption band at 3596 cm -1 of the recrystallized quartz from Mt.
Takamiyama, southwest Japan. Mineralogial Magazine 63, 693-701.
Stipp, M., Tullis, J., Behrens H. 2006: Effect of water on the dislocation creep microstructure and flow stress of quartz and
implications for the recrystallized grain size piezometer. Jouranl of Geophysical Research 111, B04201.
Fig.1: FTIR spectra for undeformed and deformed material. Absorbance is relative (left). Thin section of a deformed sample with the visibly
deformed part in the middle (right).
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Symposium 1: Structural Geology, Tectonics and Geodynamics