Influence of strike-slip fault segmentation on drainage evolution and topography. A case study: the Palomares Fault Zone (southeastern Betics, Spain)

The Palomares Fault Zone (PFZ) is one of the main sinistral strike-slip faults in the Betics (SE Spain), with approximately 16 km of north–south displacement. The PFZ initiated during the Tortonian–Messinian as a transfer structure linking areas subject to NW/SE shortening. During the Plio-Quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of Sierra Almagrera–Sierra Almenara. These Sierras, which show moderate uplift rates of 0.05–0.15 m/ka, formed in response to the oblique-slip regime of the PFZ. The drainage system in the vicinity of the PFZ is asymmetric with respect to a main axial valley that runs parallel to the PFZ on the downthrown fault block. In this block, the drainage density is lower and the streams are longer than in the uplifted block. Furthermore, west of the main axial valley the streams describe eastward directed deflections, indicating the progressive eastward migration of the main axial valley during the Pleistocene. The drainage system on the uplifted ranges shows a consequent pattern, indicating recent uplift and folding under NNW/SSE convergence. Recent activity along segments of the PFZ has increased topographical gradients, favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments.