Reply to the comment by Michard et al. on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : The Tanger-Ketama Unit (External Rif, northern Morocco) by Vázquez et al., Geologica Acta 11 (2013), 277-293"

Michard et al. (this issue) commented on certain aspects of the Alpine metamorphism and structural evolution of the Rif belt (Morocco) that were briefly noted in Vázquez et al. (2013). In particular, they criticize our interpretation of an extensional setting during the main metamorphic recrystallization of the Tanger-Ketama Unit that we considered related to slaty cleavage (S1) parallel to the lithological layering generated during the Cretaceous. Michard et al. (this issue) interpret the S1 syn-metamorphic foliation as being related to compressional folds, and the peak metamorphism temperatures, in the Lower Cretaceous sediments, as ranging between 200-300°C. Therefore, they conclude that recrystallization of the Ketama Unit occurred during Miocene thrust nappe tectonics. We explain our view in the following sections

Reply to the comment by Michard et al. on “Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: the Tanger-Ketama Unit (External Rif, Northern Morocco) by Vázquez et al., GeologicaActa 11 (2013)...

Non

Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : the Tanger- Ketama Unit (External Rif, northern Morocco)

The distribution pattern of diagenetic conditions to very low-grade metamorphism in the eastern Rif has been determined based on a study of clay-mineral assemblages and illite crystallinity of Mesozoic metapelites. Low-grade conditions were reached in marbles and also in the Beni-Malek serpentinites, as suggested by the mineral assemblages present in the marbles and antigorite growth in serpentinites. Previous thermochronological data are based on i) 40Ar/39Ar in amphiboles from greenschists, ii) K/Ar in white micas from metasandstones, and iii) fission tracks in apatites and zircons from metasandstones. These data indicate a Late Cretaceous age (∼80 Ma) for the very low- to low-grade metamorphism. We propose an evolutionary model for the Tanger-Ketama Unit consisting of a Lower Cretaceous sequence deposited in half-graben basins over an exhumed serpentinized mantle in a setting similar to the West Galician non-volcanic margin. The sediments underwent diagenesis to very low-grade metamorphism under relatively high heat flow in this extensional setting. Miocene contractional deformation of the Tanger-Ketama Unit resulted in a penetrative crenulation cleavage associated to asymmetric inclined folds. This crenulation developed, mostly by solution-transfer processes, without significant mineral growth. Miocene metamorphism reset the apatite fission-tracks, but metamorphic conditions were not high enough to reset either the K/Ar ages or the zircon fission track

Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta

Etats de surface du sol et risques de ruissellement et d'érosion

Les glissements de terrain sont des phénomènes presque ordinaires sur le littoral méditerranéen de la montagne rifaine. Le massif calcaro-dolomitique des Bokoya est marqué par des falaises à éboulements et à glissements. Sikha Asfalou, qui est situé dans le massif des Bokoya entre les deux villages "Torrès" et Badis, est un exemple de cette dynamique. Ce glissement est engendré par le recoupement de deux failles normales N85°E et N00. Il présente une rupture principale de plusieurs dizaines de mètres de commandement. Son extrémité aval montre une avancée du continent dans la mer. Les conditions lithologiques et tectoniques combinées à l'abrasion marine et à l'activité sismique récente, expliquent le rôle impressionnant des glissements dans l'évolution de cette portion du littoral méditerranéen. Ce dynamisme représente, dans cette région, un handicap à la réalisation de projets éventuels d'aménagement. (Résumé d'auteur

Reply to the comment by Michard et al. on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: The Tanger-Ketama Unit (external Rif, northern Morocco) by Vázquez et al., Geologica Acta 11 (2013)

Non

Reply to the comment by Michard et al. on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : The Tanger-Ketama Unit (External Rif, northern Morocco) by Vázquez et al., Geologica Acta 11 (2013), 277-293"

Michard et al. (this issue) commented on certain aspects of the Alpine metamorphism and structural evolution of the Rif belt (Morocco) that were briefly noted in Vázquez et al. (2013). In particular, they criticize our interpretation of an extensional setting during the main metamorphic recrystallization of the Tanger-Ketama Unit that we considered related to slaty cleavage (S1) parallel to the lithological layering generated during the Cretaceous. Michard et al. (this issue) interpret the S1 syn-metamorphic foliation as being related to compressional folds, and the peak metamorphism temperatures, in the Lower Cretaceous sediments, as ranging between 200-300°C. Therefore, they conclude that recrystallization of the Ketama Unit occurred during Miocene thrust nappe tectonics. We explain our view in the following sections

Etats de surface du sol et risques de ruissellement et d'érosion

Les glissements de terrain sont des phénomènes presque ordinaires sur le littoral méditerranéen de la montagne rifaine. Le massif calcaro-dolomitique des Bokoya est marqué par des falaises à éboulements et à glissements. Sikha Asfalou, qui est situé dans le massif des Bokoya entre les deux villages "Torrès" et Badis, est un exemple de cette dynamique. Ce glissement est engendré par le recoupement de deux failles normales N85°E et N00. Il présente une rupture principale de plusieurs dizaines de mètres de commandement. Son extrémité aval montre une avancée du continent dans la mer. Les conditions lithologiques et tectoniques combinées à l'abrasion marine et à l'activité sismique récente, expliquent le rôle impressionnant des glissements dans l'évolution de cette portion du littoral méditerranéen. Ce dynamisme représente, dans cette région, un handicap à la réalisation de projets éventuels d'aménagement. (Résumé d'auteur

Les monuments historiques de la ville de Rabat (Maroc): étude des processus d’altération et propositions de solutions durables de prévention et de restauration.

Workshop International «Patrimoine géologique, géotourisme et développement durable de la région de Rabat Salé Zemmours Zaers, la Province de Khémisset

Structure and exhumation of the Cap des Trois Fourches basement rocks (Eastern Rif, Morocco)

The Cap des Trois Fourches (Eastern Rif, northern Morocco) metamorphic basement exposes two major tectonic units, namely the Taïdant unit underthrusting the overlying Tarjât tectonic unit. The Tarjât tectonic unit is composed of metamorphic rock originating from detrital material. This upper Tarjât tectonic unit exhibits: (1) orthogneiss bodies being Paleozoic in age and (2) evidences showing a retromorphose during the Alpine orogenesis. U-Pb SHRIMP zircon geochronology from the orthogneiss bodies has yielded Sakmarian (early Permian) ages for the intrusion of their protoliths. The lower Taïdant unit is formed of green and brown shales associated with quartzite beds. A Mesozoic age is commonly accepted for this unit. The internal structure of the Tarjât tectonic unit consists in km-scale folds trending ENE-WSW with an up-dip direction towards the SE. This compressional deformational stage was superimposed on internal thrust sheets controlled by ductile shear zones with a SW-vergent transport sense. The lower Taïdant unit shows conspicuous bedding associated with a penetrative foliation outlining a monocline structure dipping gently towards the NW. The major ductile-brittle detachment fault bounding the upper Tarjât tectonic unit from the lower Taïdant unit –i.e. the local basement– exhibits evidences for a top-to-the-west sense of motion. We assume that this specific fault is the prolongation into the Cap des Trois Fourches area of the extensional detachment previously described in the Temsamane area. Therefore, this low angle detachment fault is a major tectonic element extending hundreds of km through the Eastern Rif. We postulate that this major detachment roots deep in the Eastern Rif basement. This detachment is cut at the surface by the Nekor normal-sinistral strike-slip fault that separates thin 24–32 km thick metamorphic Eastern Rif crust from the 50–55 km thick crust of the Western Rif. This transtensive fault system exhumes the Rif middle crust, represented by the Temsamane massif units, along the Nekor sinistral STEP boundary at the southern edge of the Betic-Rif subduction system.We acknowledge the financial support of research grants CGL2015-71692-P and CGL2015-67130- C2-1-R from the Spanish Ministry of Economy and Competitiveness (MINECO/FEDER, Spain). This work has received funds from the FP7-Marie Curie Action IRSES-MEDYNA funded under Grant Agreement PIRSES-GA- 2013-612572. We want to thank Aitor Cambeses for his help with the geochemistry and geochronology of the orthogneisses, and Fernando Nieto for his help with the adquisition and interpretation of the XRD data