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| Titel |
Temporal and spatial organisation of faulting in frictional wedges |
| VerfasserIn |
B. C. L. Mary, Y. M. Leroy, B. Maillot |
| 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 |
250067999
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| Zusammenfassung |
| The spatial and temporal organization of thrusting in accretionary wedges and in
fold-and-thrust belts results from the coupling between tectonics, erosion and the degradation
of the rock strength along faults. A quantitative assessment of this coupling is presented,
based on a simple approach which combines geometrical construction and evolution of
developing thrust-related folds and optimization techniques based on limit analysis. We
consider the simple prototype of a triangular wedge resting on a basal layer, the overall lying
on a straight décollement, and consider large shortenings corresponding to several million
years.
Our understanding of frictional wedges is based on the critical taper theory of Dahlen
(1984) and the introduction of the critical topographic slope αc function of the basal
décollement dip β and of the material frictional properties. If the average topographic slope α
is less than αc , the relief builds-up until αc is reached from a sequence of forward folds. This
sequence is interrupted by the activation of out-of-sequence thrusts which are contributing
to the modification of the average topographic slope. The recurrence time of this
activation is function of the distance to the front and also of the thickness of the
basal layer. This last parameter becomes inportant once the deformation reaches the
front of the wedge. Once αc is globally attained, a steady state is reached and the
spatial organization of the deformation can be seen as two propagating "waves" of
deformation, one spread from the rear, the second from the front. These two waves
recurrently enter in spatial resonnance, but the global effect of this last point is not
clear.
Damage along activated thrusts, reflected by a drop in the friction angle, perturbs the
periodicities both in time and space. Erosion controls the direction of the major thrusts as
well as preferential localization of the deformation. This can lead to the exhumation of basal
material. Comparison with large shortening sandbox experiments with erosion (Malavieille,
2010) brings new insights on the mechanisms of rotation and exhumation of originally deep
materials. A study of the strength evolution during deformation with erosion/sedimentation is
also proposed. The main result of this study is the predominant role of the geometry, and
subsequently of the topography, on the spatial and temporal organisation of the deformation. |
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