International Geologiical Congress - Oslo 2008


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STN-01 General contributions to neotectonics


Drainage anomalies areas as soft-linkage indicators in Quaternary linked fault systems


Carla Terrizzano, University of Buenos Aires - CONICET (Argentina)
Jose Maria Cortes, University of Buenos Aires - CONICET (Argentina)


Contractional active deformation of Quaternary alluvial deposits in piedmont environments becomes evident from an accentuated relief modification to subtle perturbations of fluvial geomorphologic elements.
On the one hand, the cumulative deformation associated to growth structures develops tectonically controlled topographic highs (TH) characterized by definite and clear borders, lineal, trapezoidal or irregular design at surface. This phenomenon takes place when the tectonic uplift rate is greater than the erosion and sedimentation rate. These features are mainly related to faults, folds, faulted blocks, push-up structures and imbricate thrusts.
On the other hand the subtle tectonic perturbation of the fluvial landforms becomes evident by different kinds of drainage anomalies such as deflected streams, asymmetric basins, zonal variations in drainage density, anomalous marshes or alluvial fills, anomalous stream sinuosity and incision anomalies. The association of these geomorphologic features defines tectonically controlled drainage anomalies areas (DAA), which are characterized by indefinite or diffuse borders and lineal, trapezoidal or irregular design at surface. These elements are associated with subtle uplift, rotation, propagation or migration of structures.
A detailed study of drainage areas of anomalous behavior is a useful tool at the moment of determining slight tilting and ductile strain, for example in fault bridges, which works as soft linkage zones between major structures.
An analysis of the distribution and spatial relationship between the tectonically controlled topographic highs and the tectonically controlled drainage anomalies areas at piedmont plains of western Argentine Precordillera (31°40'-32°20' SL) has made possible to elucidate the role of the drainage anomalies areas as a superficial expression of soft-linkage areas in fault systems. The tectonically controlled topographic highs would be interpreted as isolated features without the consideration of subtle drainage anomalies between them. However, the set of tectonically controlled topographic highs linked by tectonically controlled drainage anomalies areas makes possible to clarify major regional structures like Quaternary deformation belts on their initial development stages.


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