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| Titel |
Wavelength selection and evolution in high-resolution 3D numerical models of multilayer detachment folding |
| VerfasserIn |
N. Fernandez, B. J. P. Kaus |
| 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 |
250064837
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| Zusammenfassung |
| Many fold-and-thrust belts are dominated by crustal scale folding that exhibits fairly regular
fold spacing. For example, the Fars region in the Zagros Mountains shows a fold spacing
with a normal distribution around a dominant wavelength of 14 Km ± 3 Km, yet
having a wide variability of aspect ratios (length to wavelength ratios; Yamato et al.,
2011). To which extend this is consistent with a crustal-scale folding instability or
how the regional spacing of folding can be used to constrain regional rheological
parameters are not fully resolved questions. To get insights into these problems
we have investigated the dominant wavelength selection and evolution in a true
multilayer system (Schmid and Podlachikov, 2006) with three different viscosities: lower
salt layer (ηs), and overlying weak layers (ηw) and competent layers (ηc). This
has been done by means of two tools: a semi-analytical solution and numerical
models.
The 2D semi-analytical approach was applied to derive mechanical phase diagrams that
can be used to distinguish different folding modes using two viscosity ratios (R1= ηc/ ηs and
R2= ηc/ ηw). To test the validity of the phase diagrams beyond the initial stages of folding for
which the analytical approach is valid, we performed several 3D high-resolution forward
numerical runs using a finite element code (LaMEM).
Additionally, irregular bottom topography was implemented in the numerical
runs in order to account for variable salt thickness distribution and consequently
study its effect on the wavelength selection. A straight but gradual salt thickness
variation, sudden thickness variations due to a basement step or an arc shaped salt
basin among other cases could be investigated. It was observed that the bottom
topography exerts an impact on the velocity field of the different folding modes and as a
result, its influence can be observed on the resulting topography. However, not all
the folding modes exhibit an initial wavelength that is dependent on the basal salt
thickness.
The fold wavelength of the 3D simulations was extracted using 1D spectral analysis and
its evolution and selection during deformation was tracked. Furthermore, the forward
numerical simulations could be used to investigate the evolution of amplitude and
aspect ratio of the folds, as well as the interaction between different individual
folds.
The final wavelength that is selected during strain in the performed numerical simulations
is in fact in agreement with the calculated phase diagrams. Therefore, the fold spacing and
other regional observations in natural examples of folded belts could be used together with
3D numerical runs and a semi-analytical approach to successfully constrain the effective
viscosity structure of the deformed layers.
References
Schmid, D.W. and Podladchikov, Yu.Y., 2006. Philosophical Magazine, 86:21. p.
3409-3423.
Yamato, P., Kaus, B.J.P. , Mouthereau, F., and Castelltort, S., 2011. Geology. Vol 39. No
9. p. 815-818 |
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