strain evolution, scaling, analogue modelling, plateau, Central Andes
Deformation processes and their basic mechanisms are widely understood, whereas the knowledge about the distribution of strain accumulation in space and time on various scales is still insufficient. However, this is crucial for the determination of the dominant deformation frameworks (e.g., continuum-Euclidean model, block model, fractal complexity).
In this thesis, the distribution of strain accumulation on the orogen scale is examined, both in space and in time (geological long-term deformation), plus its interaction with the next smaller regional scale. The analysis is carried out on a comprehensive data base on deformation activity in the Central Andes (17-27°S and 69-63°W), complemented by artificial data from analogue simulations (two experimental series) monitored by a high-resolution system employing particle imaging velocimetry (PIV).
By means of statistics and geostatistics, characteristic scale lengths of active structures and their typical duration for the regional scale can be quantified. On the orogen scale, the scale lengths are multiples of these values, as the orogen scale represents a summary of the active structures on the regional scale, being adjacent and coevally active. These scale lengths are artefacts resulting from the current resolution of the data set.
In analogue models, the effect of both intrinsic and external parameters on the
resulting strain pattern for the above mentioned scales is analyzed. Firstly, the experiments show that threshold values exist for coupled parameters of both basal (20%) and internal (35%)
strength contrasts, which determine if either wedge-like or plateau-style settings will result. These threshold values indicate the absence of gradual transitions between the two end members.
The experiments also reveal parameter combinations for the plateau initiation including the growth of two anticlinal hinges enclosing an undeformed basin, which is subsequently drained. Driving parameters can be ranked first or second order, influencing the pattern on the orogen scale or the next smaller regional scale, respectively. Thus, the effect of controlling parameters is scale-dependent.
In spite of such an unusually well resolved data set on strain accumulation both in space and time from nature, we cannot conclusively distinguish the varying deformation frameworks, possibly due to a still insufficient data resolution. Depending on the applied resolution, we might unintentionally integrate data from different scales, so that their original strain pattern cannot be identified. It is nevertheless likely that dominant frameworks alternate over time.
The strain distribution pattern does not provide conclusive information on the underlying
deformation mechanisms. For example, both strain weakening and strain hardening can affect a
deformation system that is basically fractal. Such deformation modes can coincide with the different deformation frameworks. Both likely alternate in space and time and so does their effect on different scales. Generally, the lack of highly resolved data precludes the identification of the respective patterns and deformation modes.
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