Relative landscape maturity in the South Rifian Ridges (NW Morocco): Inferences from DEM-based surface indices analysis

Abstract

In this paper we present the first landscape maturity analysis of the South Rifian Ridges, part of the southern branch of Gibraltar Arc (Morocco). Since the late Miocene, the southward propagation of anticlines structures is driven by the convergence between the Nubia and Eurasia plates, leading to the closure of the South Rifian Corridor and the ongoing motion of the Rif cordillera. So far little is known about the relative activity and the present-day evolution of the ridges. By using DEM-based geomorphic indices, we assessed the relative activity of the Moulay Idriss Massif anticlines to distinguish the most recent structures; and to have a clearer insight on the Quaternary evolution in the front of Rif fold-thrust belt. We used indices including the Hypsometric Integral (HI), Surface Roughness (SR) and their combination, Surface Index (SI), to highlight raised surfaces and erosional discontinuities. The normalized steepness index (Ksn) for the streams is evaluated to detect vertical displacements from the drainage network analysis. The topographic swath profiles are analyzed to highlight elevated and highly dissected areas. The relative landscape maturity analysis suggests that the entire massif has started to uplift at the same time and it exhibits a variation in landscape maturity in response to differential rates of exhumation, which increase from the east to the northwest (in Fert El Bir anticline). These differences resulted in variations in structural control that might be favored by salt layer at depth and stimulated by recent plate’s shortening phases.