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| Titel |
Décollement controls on strain distribution in mountain belts: insights from numerical models. |
| VerfasserIn |
Arjan R. Grool, Ritske S. Huismans, Mary Ford |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127429
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| Publikation (Nr.) |
 EGU/EGU2016-7307.pdf |
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| Zusammenfassung |
| Doubly vergent orogens have a pro-wedge (lower plate) and a retro-wedge (upper plate).
Most shortening is accommodated in the pro-wedge while retro-wedge shortening is typically
limited. For example, the Eastern Pyrenees have experienced about 145 km of convergence,
of which about 125 km (86%) was accommodated in the pro-wedge and about 20 km (14%)
in the retro-wedge. Strain partitioning between pro- and retro-wedge is influenced by several
factors, some of which have been identified in past work: Extensional inheritance and
syn-orogenic sedimentation can help to increase the percentage of total shortening
accommodated in the retro-wedge while erosion promotes pro-wedge shortening. We use
high-resolution 2D numerical models to investigate factors that control pro- versus
retro-wedge shortening. For a total convergence similar to the Eastern Pyrenees, our models
predict that variations in extensional inheritance and syn-orogenic sedimentation will result in
a maximum of 10% of total shortening being accommodated in the retro-wedge.
Here, we investigate the role of 1) the rheology and 2) distribution of a décollement
layer.
Our models show that: 1) Décollement rheology has a first order control on strain distribution
between the pro- and the retro-wedge. After 145 km of total convergence, a model with a
weak frictional (ϕ=2, shale-like) décollement will only accommodate 10% of total shortening
in the retro-wedge. In contrast, in models with a weak viscous (μ=1018, salt-like)
décollement retro-wedge shortening amounts to 18% and a stronger, but still weak, viscous
décollement (μ=1019) leads to 21%. 2) Décollement distribution influences the timing of the
first outward propagation of thick-skinned deformation in the retro-wedge. In the Eastern
Pyrenees, thick-skinned deformation propagated out into the retro-wedge within 145 km of
total convergence. In models with a décollement on both sides of the orogen this only
occurred after 240 km. If, as in the Eastern Pyrenees, the décollement is missing
in the model’s retro-wedge, the required convergence would be reduced to 180
km.
Assuming deformation localizes along the path of least resistance, meaning a force
balance exists between the pro- and retro-wedge, anything that changes the force
required to deform one side of the orogen will have direct consequences for the other
side as the strain distribution adjusts. In our models a viscous décollement enables
the sedimentary cover of the pro-wedge to be transported into the pro-foredeep,
increasing the force required for pro-wedge frontal accretion and thus promoting
shortening in the retro-wedge. In models with no décollement in the retro-wedge,
higher friction along existing crustal shear zones will accelerate formation of a new,
more external shear zone. This mechanism alone cannot explain frontal accretion in
the retro-wedge after only 145 km of convergence, meaning other factors such
as more pre-existing extensional shear zones may also play a role in the Eastern
Pyrenees. |
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