A new lithostratigraphic framework for the Anti-Atlas Orogen, Morocco

A new lithostratigraphic nomenclatural framework is proposed for the Anti-Atlas Orogen of Morocco, to replace the previous chronostratigraphic scheme. All the lithostratigraphic units of the Anti-Atlas Orogen are well represented in the Sirwa, Kerdous and Sarhro inliers and examples from these areas are given prominence, though correlates in other areas are given, where known. The oldest, Palaeoproterozoic, rocks of the cratonic basement form the northern part of the West African Craton and can be subdivided into a series of Complexes (made up of constituent Groups, Suites etc.), depending on geographical outcrop (e.g. the Zenaga and Kerdous Complexes in the Sirwa and Kerdous inliers respectively). The Neoproterozoic rocks deposited on this basement are termed the Anti-Atlas Supergroup, within which five groups of volcano–sedimentary units (Taghdout, Jbel Lkst, Sarhro, Iriri, and Bou Azzer Groups) and various intrusive igneous rocks are recognised (e.g. Ifzwane and Toudma Suites). These units are related to the earliest passive margin, oceanic and island-arc development phases of the orogen between 800 and 660Ma. The earliest Pan-African deformation (at 660Ma) resulted from closure of the ocean basin, SW-directed thrusting and accretion of the island-arc remnants. Continued prolonged convergence gave rise to a sinistral transpressional regime in which late syn- to post-tectonic continental volcanic and clastic sequences of the Ouarzazate Supergroup were deposited. The first rocks of this new tectonic regime were deposited in narrow, tectonically active, strike-slip pull-apart rift basins (Bou Salda, Mgouna, Tafrawt and Anzi Groups) associated with intrusion of high-K calc-alkaline granitoid batholiths (e.g. Assarag, Bardouz Suites) and the juxtaposition of ophiolitic remnants in major strike-slip shear belts. These were followed by the deposition of the much more areally extensive continental volcano–sedimentary molasse, the volcanic components of which were erupted from several interfingering volcanic centres, often associated with caldera complexes and sub-volcanic alkaline granites (Toufhgrane, Tanghourt and Guellaba Suites). The proposed lithostratigraphic scheme encompasses all the major rock units identified in the literature from the orogen and is flexible so that new, lower-ranking, units can be placed at the appropriate stratigraphic level in future. This framework is supported by new high-precision U–Pb zircon dates that have recently become available

The basic magmatism in the Famennian-Dinantian Sidi Bettache Basin (Northwest Hercynian Morocco): new facts

Commonly is held up that the Sidi Bettache Basin corresponds to the collapse of a large block of the middle Devonian carbonate platform with subsequent magmatic injections emplacement along its boundaries. Previous studies of one of us (A.L.) and those in progress show instead that this magmatism is primarily controlled by distensional activity of NNW-SSE to NW-SE faults before Middle Visean time. These faults affect throughout the 60 km wide western part of the basin which is also characterized by its Famennian-Lower Visean sedimentary evolution and by a complex variscan polyphasic structuratio

Late Visean synsedimentary compressive tectonism into the Sidi Bettache Basin (northwestern Moroccan Meseta)

Este trabajo constituye una versión española del capítulo 1.4: “Tectónica sinsedimentaria” de la Tesis de Estado defendida en el año 2002 por Abdellah Lakhloufi, para obtener el grado de Doctor en Ciencias por la Universidad de Rabat. En el texto que se presenta se ha intentado respetar al máximo la estructura y desarrollo del manuscrito original, así como sus figuras y gráficos, introduciendo sólo algunas de las numerosas observaciones formuladas por los revisores, aunque, con el fin de no modificar demasiado dicho texto no se hayan podido tener en cuenta otras igualmente importantes.Para explicar la apertura y evolución de la cuenca fameno-dinantiense de Sidi Bettache (BSB; Meseta noroccidental marroquí), han sido propuestos modelos de pull-apart y de transtensión-transpresión. Sin embargo, en ausencia de argumentos plausibles, estos modelos han permanecido como puramente conceptuales. Nuestra contribución corrobora el segundo modelo con la puesta en evidencia de una fase transpresiva durante la evolución de la BSB. En este sentido, mostramos la existencia, en la parte occidental de la cuenca, de una deformación compresiva sinsedimentaria intra-Viseense Superior asociada localmente a una deformación distensiva. En términos de tectónica analítica, nuestros datos ponen énfasis en el análisis geométrico de las rampas y la evolución de un cabalgamiento que aprovecha este tipo de estructuras tectónicas durante su propagación. Finalmente, desde el punto de vista geodinámico, el campo de acortamiento ha sufrido una rotación antihoraria entre el Fameniense Superior (edad de apertura de la BSB) y el Viseense Superior, pasando del ENE-WNW al NE-SW.Pull apart and transtension –transpression models were successively proposed to explain the openning modalities and the evolution of the Famennian-Dinantian Sidi Bettache Basin (BSB). However, these two models remained purely conceptual. The objective of our contribution is to support the validity of the second model. Thus, we give evidence of an intra Late Visean synsedimentary compressive deformation in the western part of the BSB associated, locally, with a distensive tectonic. In terms of analytic tectonic, our data are focussed essentially on geometric analysis of ramps and the evolution of an overthrusting making use of this type of tectonic structures for its propagation. From the geodynamic point of view, the BSB shortening field azimuth has undergone a relative counterclockwise rotation between the Late Famennian (when SBB was open) and the Late Visean, switching from the ENE-WSW to the NE-SW direction.Les modèles de pull-apart et de transtension-transpression ont été successivement proposés pour expliquer l’ouverture du Bassin famenno-dinantien de Sidi Bettache (BSB) et son évolution. Néanmoins, à défaut d’arguments plausibles, ces deux modèles sont restés purement conceptuels. Notre contribution corrobore le deuxième modèle en mettant en évidence la réalité d’une phase transpressive dans l’évolution du BSB. Dans ce sens, nous montrons l’existence, dans la partie occidentale du bassin, d’une déformation compressive synsédimentaire intra-Viséen Supérieur qui associe localement une déformation distensive. En terme de tectonique analytique, nos données portent essentiellement sur l’analyse géométrique des rampes et l’évolution d’un chevauchement qui utilise ce type de structure tectonique lors de sa propagation. Enfin, sur le plan géodynamique, le champ de raccourcissement a subi une rôtation anti-horaire entre le Famennien Supérieur (âge d’ouverture du BSB) et le Viséen Supérieur. Celui-ci passe de la direction ENE-WSW á celle NE-SW.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Las doleritas neoproterozoicas de las ventanas de Agadir Melloul y del Adrar Izazen (Anti-Atlas Central, Marruecos). Restos de una distension pre-panafricana

Two swarms of diabasic dykes wich différents directions NE-SW and NW-SE cut the socle of Agadir Melloul and the Adrar Izazen neoprotero/.oic windows. This rocks show a hidrothermal transformation simultanely wich Pahafricàn deformation but the primary mineralógicaI composition preserved are formed by: plagioclase, augite, ilmenite and micropegmatite textures wich hornblende and biotite ocasionally. Their chemical composition are tholeitic and transitional basalts in the two directions respectively mentioned. This magmatism have an anorogenic continental character and it is related wich the extensif pre-panafrican phase that involved to northern edge of western african crato