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| Titel |
Deformation initiation and localization around inclusions |
| VerfasserIn |
Luiz F. G. Morales, Erik Rybacki, Georg Dresen |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074316
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| Zusammenfassung |
| Deformation localization along narrow zones of variable scales is a common feature in
orogenic belts. Although there are a number of studies that focus on the evolution of
brittle fault zones, little is known about the initiation and localization of ductile
shear zones. To study the nucleation and evolution of high temperature shear zones,
we performed shear experiments in marbles containing structural heterogeneities
and analyzed the deformation microstructures and the resulting crystallographic
orientation. Cylindrical samples of coarse-grained Carrara marble containing one or two
1 mm thin artificially prepared sheets of fine-grained Solnhofen limestone were
deformed in a Paterson-type gas deformation apparatus at 900 Ë C temperature and
confining pressures of 300 and 400 MPa. Three samples were deformed in axial
compression at a bulk strain rate of 8x10-5s-1to axial strains between 0.02 and 0.21
and 15 samples were twisted in torsion at a bulk shear strain rate of 2x10-4s-1to
shear strains between 0.01 and 3.74. At low strains, intense twinning of calcite is
observed in the calcite grains of Carrara marble near the inclusion. The distance from
the tip of the inclusion in which twinning is observed increases with increasing
strain. Orientation of the twin planes may vary from parallel to normal to the tip
of the inclusion, and with increasing strain there is a tendency of development of
“twin conjugates”. Together with twinning, subgrain boundaries are observed in this
region, possibly followed by initial grain size reduction. In these experiments, strain
is localized into narrow bands, as revealed by misorientation maps showing the
degree of internal lattice distortion of individual calcite crystals around the tip of
the inclusion, reaching values from 3 to 10Ë , depending on the strain. Internal
misorientation of grains increases with decreasing distance to the inclusion. Strain is
localized into narrow, long bands extending several mm into the matrix. The degree
of localization decays exponentially with increasing distance from the tip of the
inclusion. A weak initial development of crystallographic orientation along this process
zones is evident starting at very low strains, increasing in strength with increasing
strain. The microstructural modifications observed at the tip of the inclusions are
possibly caused by the stress concentration in this region. Towards higher strains,
deformation of calcite grains progressively affects the surrounding of the inclusions.
Our results demonstrate the importance of structural and stress heterogeneities for
the nucleation and formation of localized shear bands at elevated temperatures. |
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