From extension to transpression: Quaternary reorganization of an extensional-related drainage network by the Alhama de Murcia strike-slip fault (eastern Betics)

- We analyze a geomorphologically changing tectonic scenario.
- Alhama de Murcia fault and Tercia anticline are the active structures in the area.
- The drainage reorganization can be analyzed by geomorphic indexes.

The complex present-day drainage network of the Lorca-Totana area records the changing tectonic setting, from extension to transpression, in the eastern Betics. Through a detailed morphometric analysis we evaluate the topographic response to this major change in the tectonic setting and the influence in the drainage of Miocene extension and middle Pleistocene to present day transpression. The present-day drainage network preserves geomorphic features inherited from Late Miocene extension that are being overprinted by a new transverse fluvial system. This new system advanced towards the NW since the middle Pleistocene in response to a localized base-level drop related to the NE-SW oriented Alhama de Murcia sinistral-reverse fault. Geomorphic indexes calculated in this work suggest the present-day activity of the Alhama de Murcia fault and the Sierra de la Tercia anticline, the two major tectonic structures in the area. The landscape rejuvenation associated with this process results in: contrasting mountain front sinuosity values between old and new mountain fronts, high SLk index anomalies, convex-shaped and complex hypsometric curves, knickpoints in river profiles, contrasting slope-area plots and high steepness index values. This fluvial reorganization was driven progressively by successive fluvial captures preserved as wind-gaps in the present-day drainage network.