The structure of the Temsamane fold-and-thrust stack (eastern Rif, Morocco): Evolution of a transpressional orogenic wedge

Abstract

The structure of the Temsamane fold-and-thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds. This ductile stack was formed in an inclined left-handed transpressional zone at the North African paleomargin during Chattian to Langhian times producing two main deformational events. The first event (D-p) produced a S-p/L-p planar linear fabric generated in a noncoaxial deformation with a top-to-the-WSW sense of movement and was associated to metamorphic P-T conditions varying from late diagenesis in the southernmost Temsamane outcrops to epizone in the north. According to the Ar-40/Ar-39 ages, this deformation occurred at Chattian-Aquitanian times. The second deformational event (D-c event) generated ENE-WSW trending folds with SSE vergence and a set of anastomosing shear zones with S-m/L-m planar linear fabric. The latter units were generated at around 15 Ma (Langhian), and indicate a strong localization of the simple shear component of the transpression. Moreover, this orientation is compatible with the kinematics of the Temsamane detachment, which can explain most of the uplift of the Temsamane rocks from the middle to the uppermost crust. The described evolution indicates that collision between the western Mediterranean terranes and the North African paleomargin and the formation of the Rifean orogenic wedge occurred at Chattian to Langhian times.