Mauretanian flysch nappe in the northwestern Rif Cordillera (Morocco): deformation chronology and evidence for a complex nappe emplacement

Abstract

Abstract This study deals with the Mauretanian flysch nappe in the southern side of the Gibraltar Strait, NW of the Rif belt (Morocco), where it is possible to better appraise the stacking pattern of its two structural components (the Tisirene and Béni Ider nappes), and to decipher the chronology of deformation and its structural relationships with the overlying (Predorsalian and Numidian nappes) and the underlying nappes (Melloussa and Intrarif units). It is found that the main deformations were produced by an intermittent compressional regime, during which north-south- to NW-SE-directed compressional phases alternated with ENE-WSW to east-west-directed compressional ones. Whereas the former were generated by the Africa-Iberia convergence and resulted in small-scale thrusts and a brittle deformation style, the latter were driven by the west-drifting Alboran plate and resulted in paroxysmal fold-thrust deformations. Field evidence shows that the emplacement of the Mauretanian nappe over the Massylian one and the Intrarif units operated by inter-related compressional and gravitational processes, by virtue of which the majority of nappes stacked in an out-of-sequence regime. The precise age of the paroxysmal phases remains uncertain because of paucity or absence of direct stratigraphical data. However, this structural evolution is likely to have started as early as the mid-Burdigalian, when sedimentation synchronously ceased in the flysch trough. Its final phases may be placed precisely between the Langhian (N8) age of the most recent formations overlapped by these nappes and the late Tortonian age of the oldest formations transgressively covering them.