EVIDENCES OF DRAINAGE NETWORK REORGANIZATION IN RESPONSE TO ACTIVE TECTONICS IN THE BETICS CORDILLERA, SPAIN

The Betics Cordillera is part of a circum Mediterranean orogen, associated with rapidly opening backarc basins, which formed through subduction rollback ± delamination process coincident with orogenesis, and extend from Europe into Africa through the Gibraltar Arc.

Several geodynamic models have been proposed in the literature and despite recent geophysical investigations, open questions remain on the temporal and spatial relationship between trust belt contraction, intermountain basin evolution, extension and uplift.

The goal of this research is to investigate the presence of a spatial pattern in drainage basin evolution that can support the hypothesis of time transgressive uplift over sectors of the Betic Cordillera that can be interpreted as the surface response to deeper crustal dynamics.

The study is based on the analysis of topographic and morphometric indexes of 5 river basins that drain the south-east sector of the Betics to the Alboran Sea. These rivers have been analyzed in Slope-Area space to extract steepness and concavity, which allow to reconstruct the geometry of paleo-courses and relate it to paleo-base levels.

The results from different analysis can be synthetized as follows:

- the hypsometric integrals show that landscape has increasing disequilibrium signature moving from East to West;

- long profiles in combination with Hack index analysis show a series of knickpoints that correlate to relict paleosurfaces, and suggest a recent reorganization of the drainage network, with possible river captures;

- the analysis of chi integral suggest that the Adra river, located in the center of the area of investigation, is currently aggressing the surrounding drainages.

In conclusion the results suggest that the wester sector of the Sierra Nevada is experiencing a strong and relatively young rejuvenation, as a consequence of differential uplift. This findings inform on the possibility that the geodynamic processes acting in the area should be interpreted as localized delamination rather than a simple classic slab rollback model.