No abstract

The High Atlas of Morocco is a double-vergent mountain belt developed by Cenozoic shortening and inversion of a Triassic-Jurassic rift. The structural setting, the morphometric features, and the patterns of exhumation through time and space change remarkably both along and across the strike. Here we combine structural data with revised thermochronological data to unravel the kinematic and evolution of the western High Atlas. Our results show that the structural grain of the western High Atlas is defined by two main groups of faults, namely, thrust and oblique-slip faults, which mainly strike subparallel from W-E to NE-SW. The slip direction of the thrust structures is NNW-SSE to NW-SE oriented, and the slip direction of the oblique-slip faults is WSW-ENE to NW-SE oriented. Pieces of thermochronological and geological evidence indicate that in the last~10 Ma the exhumation rate increased during the activity thrusts and oblique-slip faults. The coexistence of these two fault systems also suggests partitioning of deformation under a transpressive regime. In the western High Atlas, we estimate a displacement of~12 km on the frontal thrusts and of at least~22 km on the axial oblique-slip structures. Thrusts and oblique-slip structures together result in a total cumulative displacement of~25 km, which represents about half of the Africa-Eurasia convergence.

No abstract

Deciphering Variscan versus Alpine history in the Internal Rif system is a key to constrain the tectonic evolution of the Alboran domain and hence the geodynamics of the western Mediterranean system during the Cenozoic. This study focuses on the evolution of the metamorphic envelope of the Beni Bousera massif and its relation to the underlying peridotites. Combining structural geology, metamorphic petrology, and laser ablation inductively coupled plasma mass spectrometry U-Th-Pb dating of monazite, this study contributes to the understanding of the tectonic history of the western Internal Rif. The regional foliation (S2) is characterized by low pressure-high temperature (LP-HT) mineral assemblages and obliterates a former foliation (S1) developed along a Barrovian (medium pressure-medium temperature, MP-MT) metamorphic gradient. The dating of some metamorphic monazite grains from a micaschist and a migmatitic gneiss demonstrates that the crustal envelope of the peridotite recorded two distinct tectonometamorphic episodes. Data from monazite inclusions in S1 garnet suggest that the first event, D1, is older than 250-170 Ma and likely related to the Variscan collision, in agreement with the Barrovian type of the metamorphic gradient. The second event, D2, is Alpine in age (at circa 21 Ma) and corresponds to a strong lithosphere thinning allowing subsequent subcontinental mantle exhumation. Such a tectonic context provides an explanation for the LP-HT metamorphic gradient that is recorded in the regional foliation of the western Betic-Rif system. This extension is probably related to a subduction slab rollback in the western end of the Mediterranean realm during the Oligo-Miocene times. No evidence for a Tertiary high pressure/low temperature metamorphism has been identified in the studied area.