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| Titel |
Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling |
| VerfasserIn |
L. Pourhiet, B. Huet, L. Labrousse, K. Yao, P. Agard, L. Jolivet |
| 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. 1 ; Nr. 4, no. 1 (2013-04-17), S.135-152 |
| Datensatznummer |
250017768
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| Publikation (Nr.) |
 copernicus.org/se-4-135-2013.pdf |
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| Zusammenfassung |
We have designed a series of fully dynamic numerical simulations aimed at
assessing how the orientation of mechanical layering in rocks controls the
orientation of shear bands and the depth of penetration of strain in the
footwall of detachment zones. Two parametric studies are presented.
In the first one, the influence of stratification orientation on the
occurrence and mode of strain localisation is tested by varying initial dip
of inherited layering in the footwall with regard to the orientation of
simple shear applied at the rigid boundary simulating a rigid hanging wall,
all scaling and rheological parameter kept constant. It appears that when
Mohr–Coulomb plasticity is being used, shear bands are found to localise only
when the layering is being stretched. This corresponds to early deformational
stages for inital layering dipping in the same direction as the shear is
applied, and to later stages for intial layering dipping towards the opposite
direction of shear. In all the cases, localisation of the strain after only
γ=1 requires plastic yielding to be activated in the strong layer.
The second parametric study shows that results are length-scale independent
and that orientation of shear bands is not sensitive to the viscosity
contrast or the strain rate. However, decreasing or increasing strain rate is
shown to reduce the capacity of the shear zone to localise strain. In the
later case, the strain pattern resembles a mylonitic band but the rheology is
shown to be effectively linear.
Based on the results, a conceptual model for strain localisation under
detachment faults is presented. In the early stages, strain localisation
occurs at slow rates by viscous shear instabilities but as the layered media
is exhumed, the temperature drops and the strong layers start yielding
plastically, forming shear bands and localising strain at the top of the
shear zone. Once strain localisation has occured, the deformation in the
shear band becomes extremely penetrative but the strength cannot drop since
the shear zone has a finite thickness. |
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