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| Titel |
Finite lattice distortion patterns in plastically deformed zircon grains |
| VerfasserIn |
E. Kovaleva, U. Klötzli, G. Habler, E. Libowitzky |
| 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 ; 5, no. 2 ; Nr. 5, no. 2 (2014-11-18), S.1099-1122 |
| Datensatznummer |
250115348
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| Publikation (Nr.) |
 copernicus.org/se-5-1099-2014.pdf |
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| Zusammenfassung |
This study examines finite deformation patterns of zircon grains from
high-temperature natural shear zones. Various zircon-bearing rocks were
collected in the Western Tauern Window, eastern Alps, where they were
deformed under amphibolite facies conditions, and in the Ivrea–Verbano Zone
(IVZ), southern Alps, where deformation is related with granulite-facies
metamorphism. Among the sampled rocks are granitic orthogneisses,
metalamprophyres and paragneisses, all of which are strongly deformed.
The investigated zircon grains ranging from 10 to 50 μm were
studied in situ using a combination of scanning electron microscope (SEM)
techniques, backscattered electron (BSE) imaging, forward-scattered electron (FSE) imaging,
cathodoluminescence (CL) imaging, and crystallographic orientation mapping by
electron backscatter diffraction (EBSD), as well as micro-Raman spectroscopy.
Energy-dispersive X-ray spectrometry (EDS) was applied to host phases.
Microstructural analysis of crystal-plastically deformed zircon grains was
based on high-resolution EBSD maps. Three general types of finite lattice
distortion patterns were detected: type (I) is defined by gradual bending of
the zircon lattice with orientation changes of about 0.6–1.8° per
micrometer without subgrain boundary formation. Cumulative grain-internal
orientation variations range from 7 to 25° within single grains. Type
(II) represents local gradual bending of the crystal lattice accompanied by
the formation of subgrain boundaries that have concentric semicircular shapes
in 2-D sections. Cumulative grain-internal orientation variations range from
15 to 40° within single grains. Type (III) is characterized by
formation of subgrains separated by a well-defined subgrain boundary network,
where subgrain boundaries show a characteristic angular closed contour. The
cumulative orientation variation within a single grain ranges from 3 to
10°. Types (I) and (II) predominate in granulite facies rocks,
whereas type (III) is restricted to the amphibolite facies rocks. The
difference in distortion patterns is controlled by strain rate and by ratio
between dislocation formation and dislocation motion rates, conditioned by
the amount of differential stress.
Investigated microstructures demonstrate that misorientation axes are usually
parallel to the < 001 > and < 100 > crystallographic directions;
dominant slips are < 010 > {001},
< 010 > {100} and < 001 > {010}, whereas in
some grains cross-slip takes place. This study demonstrates that activation
of energetically preferable slip systems is facilitated if zircon grain is
decoupled from the host matrix and/or hosted by a soft phase. |
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