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| Titel |
Grain size assisted formation of pseudotachylites: A numerical study |
| VerfasserIn |
Marcel Thielmann, Antoine Rozel, Boris Kaus, Yanick Ricard |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095102
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| Publikation (Nr.) |
 EGU/EGU2014-10544.pdf |
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| Zusammenfassung |
| The processes resulting in the formation of lithospheric-scale shear zones are still poorly
understood. Among others, shear heating and grain size reduction have been proposed to be
viable weakening mechanisms to localize deformation and form lithospheric-scale shear
zones. The interplay between both mechanisms is particularly interesting, as both compete
for a part of the deformational work. High temperatures favor grain growth, therefore one
would expect larger grain sizes in shear zones that have been formed by shear heating.
However, larger temperatures increase strain rates, thus also the amount of deformational
work, which in turn would favor grain size reduction. Here we investigate the interplay
between both mechanisms using numerical models of a viscoelastic slab deforming in simple
shear, employing a viscous rheology composed of dislocation and diffusion creep.
Grain size evolution is governed by a recently developed physics-based evolution
law.
We develop scaling laws for the peak stress and the dominating deformation
mechanisms depending on various material parameters and boundary conditions. We find
that grain size reduction alone does not localize deformation in simple shear. In
conjunction with shear heating however, a localized shear zone is formed due to thermal
runaway. During this process, grain size is significantly reduced. Depending on
grain growth parameters, a mylonitic shear zone is formed in which deformation is
permanently localized and which deforms in diffusion creep. Additionally, the stress
required to initiate thermal runaway is reduced compare to cases with shear heating
alone, thus facilitating the formation of a narrow localized shear zone in the ductile
regime.
These results have several implications ranging and from simultaneous pseudotachylite
and mylonite formation at depths below the seismogenic depth to subduction initiation. |
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