DRAINAGE NETWORK REORGANIZATION AND DIVIDE MIGRATION IN RESPONSE TO ACTIVE TECTONICS IN THE BETIC RANGE, SPAIN

We present results of a tectonic geomorphology analysis of river networks along the south-east portion of the Betic Cordillera, from Guadix basin to Almeria coast, including Sierra Nevada and Sierra de Gàdor and intervening intermountain basins.

The Betic cordillera is a manifestation of the active continental collision between Iberia and the Alboran domain, as part of the complex convergence between Nubian and Eurasian plates, which is characterized in this area by the westward migration of the Betics-Rift Arc.

We observe the presence of a pattern of drainage reorganization that, starting at the coast, spread as pulses of incision to the north and east, and is responsible for river captures, inversion of drainage direction and intermountain basin integration. This is particularly evident in the area of Sierra de Gàdor, but can be observed consistently along much of the southeastern part of the south coast Spain. The initiation of the incision appears to be moving from east to west, resulting in rivers capture and beheading. We support this interpretation on the basis of morphometric analysis of river network, distribution and elevation of knickpoints and preliminary mapping of terraced river deposits. We also use the analysis of chi and tau value to asset the direction of ongoing migration of the river divides.

This wave of landscape rejuvenation leaves remnants of paleo landscape that can be used to connect the river evolution in the south to the late history of evolution of the many intermountain basins to the north (Padul, Granada, Guadix, Vera). Basins are half grabens superimposed on thrust belt wedge-top basins. To improve the age constrain of the integration of these basins we dated at ~200 ky the top surface of the Guadix basin using TCN ¹⁰Be.

Along the coast a well known suite of marine terraces records a pattern of uplift which is out of sequence with the regional uplift of Sierra Nevada, while the more recent westward passing of landscape reorganization can be traced by a series of river delta that forms following the progressing of river captures.

Our analysis of the river network arrangement and landscape evolution provides insights to understand the history of differential uplift of the central and eastern sector of the Betic range and feeds into the ongoing discussion of surface response to crustal and mantle dynamics.