ACTIVE TECTONICS IN THE MOULAY IDRISS MASSIF (SOUTH RIFIAN RIDGES, NW MOROCCO): NEW INSIGHTS FROM GEOMORPHIC INDICES AND DRAINAGE PATTERN ANALYSIS

The Moulay Idriss Ramp anticlines of the South Rifian Ridges are located in the front of the Moroccan Rif Belt (southern branch of the Arc of Gibraltar) and have accommodated the tectonic escape of this Alpine chain as an active edge, in response to the converging Eurasian and African plates. Nevertheless, recent evidences of this landscape tectonic activity remain poorly defined.

We investigated the variations in tectonic activity and evaluated its influence on the landscape evolution, through the application of geomorphic indices including: the mountain front sinuosity, valley floor width-to-height ratio, drainage basin asymmetry factor, hypsometric curves, normalized steepness index, longitudinal river profile, and χ as an indicator of drainage network disequilibrium. Morphotectonic study shows that fault related folds, in the area, produce differential uplift with a relatively high degree of tectonic activity along the eastern part of the massif. The doming process accounts for the elevation of the area, in the Dehar en Nsour salt dome, and this in turn, could be explained as being promoted by the Nzala des Oudayas fault system. On the other hand, the Moulay Idriss fault exerts a strong influence on the morphology of the Fert El Bir anticline inducing the Khoumane river deflection, while other streams exhibit rejuvenation and water divide migration.

These new data elucidate the recent tectonic evolution of folds and strike-slip fault systems in the southern front of the Gibraltar-Rif southern edge, which contributes to the movement of the Rif belt with respect of the stable Africa, and sheds new light on the ‘‘Meknes’’ earthquake, confused with the contemporaneous 1755 Lisbon earthquake.