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| Titel |
Strain localization in carbonate rocks experimentally deformed in the ductile field |
| VerfasserIn |
E. Rybacki, L. F. G. Morales, G. Dresen |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069317
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| Zusammenfassung |
| The deformation of rocks in the Earth’s crust is often localized, varying from brittle fault
gauges in shallow environments to mylonites in ductile shear zones at greater depth. A
number of theoretical, experimental, and field studies focused on the evolution and extend of
brittle fault zones, but little is known so far about initiation of ductile shear zones. Strain
localization in rocks deforming at high temperature and pressure may be induced by several
physical, chemical, or structurally-related mechanisms. We performed simple and pure shear
deformation experiments on carbonate rocks containing structural inhomogenities in the
ductile deformation regime. The results may help to gain insight into the evolution of high
temperature shear zones.
As starting material we used cylindrical samples of coarse-grained Carrara marble
containing one or two 1 mm thin artificially prepared sheets of fine-grained Solnhofen
limestone, which act as soft inclusions under the applied experimental conditions.
Length and diameter of the investigated solid and hollow cylinders were 10-20
mm and 10-15 mm, respectively. Samples were deformed in a Paterson-type gas
deformation apparatus at 900Ë C temperature and confining pressures of 300 and 400
MPa. Three samples were deformed in axial compression at a bulk strain rate of
8x10-5 s-1to axial strains between 0.02 and 0.21 and 15 samples were twisted in
torsion at a bulk shear strain rate of 2x10-4 s-1 to shear strains between 0.01 and
3.74.
At low strain, specimens deformed axially and in torsion show minor strain hardening
that is replaced by strain weakening at shear strains in excess of about 0.2. Peak
shear stress at the imposed condition is about 20 MPa. Strain localized strongly
within the weak inclusions as indicated by inhomogeneous bending of initially
straight strain markers on sample jackets. Maximum strain concentration within
inclusions with respect to the adjacent matrix was between 4 and 40, depending on total
strain and size of inclusions. The localization of strain extended into narrow, few
mm long, bands in front of the inclusions, where the degree of localization decays
exponentially with increasing distance from the tip of the inclusion. Preliminary
microstructural analysis show pronounced recrystallization of the marble within this
process zone, owing to stress concentration at the tip of the inclusion. The results
demonstrate the importance of structural defects on localization in the ductile regime. |
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