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| Titel |
Short-wavelength undulatory extinction in quartz recording coseismic deformation in the middle crust – an experimental study |
| VerfasserIn |
C. A. Trepmann, B. Stöckhert  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 4, no. 2 ; Nr. 4, no. 2 (2013-09-04), S.263-276 |
| Datensatznummer |
250084933
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| Publikation (Nr.) |
 copernicus.org/se-4-263-2013.pdf |
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| Zusammenfassung |
| Deformation experiments are carried out on natural vein quartz in a modified
Griggs-type solid medium apparatus to explore the preservation potential of
microfabrics created by crystal-plastic deformation at high stress,
overprinted during subsequent creep at lower stress. A corresponding stress
history is expected for the upper plastosphere, where fault slip during an
earthquake causes quasi-instantaneous loading to high stress, followed by
stress relaxation. The question is whether evidence of crystal-plastic
deformation at high stress, hence an indicator of past seismic activity, can
still be identified in the microstructure after overprint by creep at lower
stresses. First, quartz samples are deformed at a temperature of
400 °C and constant strain rate of 10−4 s−1 ("kick"),
and then held at 900 to 1000 °C at residual stress ("creep"). In
quartz exclusively subject to high-stress deformation, lamellar domains of
slightly differing crystallographic orientation (misorientation angle
< 2°) and a few tens of micrometres wide occur. In the
transmission electron microscope (TEM), these areas show a high density of
tangled dislocations and cellular structures. After "kick and creep"
experiments, pronounced short-wavelength undulatory extinction (SWUE) is
observed in the polarization microscope. The wavelength of SWUE is up to
10 μm, with oscillatory misorientation of up to a few degrees. TEM
inspection reveals domains with high density of dislocations and differing
diffraction contrast bound by poorly ordered dislocation walls. Only zones
with exceptional damage generated during high-stress deformation are replaced
by small new grains with a diameter of about 10 to 20 μm, forming
strings of recrystallized grains. For large original grains showing SWUE, the
Schmid factor for basal ⟨ a ⟩ glide is found to be high. SWUE
is taken to reflect high-stress crystal-plastic deformation, the modified
microstructure being sufficiently stable to be recognized after subsequent
creep as an indicator of past seismic activity. |
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