The Anti-Atlas is reviewed and examined in the light of its geodynamic significance as a Palaeozoic basin and fold belt. Shortening is accommodated by polyharmonic buckle folding of the cover in a thick-skinned fashion without the development of any significant thrust/duplex systems. The Anti-Atlas is heavily inverted deep intracratonic basin, rather than a former passive margin of the Palaeo-Tethys Ocean. Inversion took place in Late Carboniferous to Early Permian times. Main shortening directions changed from NW-SE to north-south and maybe NE-SW through time, leading to the development of dome and basin patterns on scales from 100 m to 10 km.

The late Variscan Anti‐Atlas of Morocco shows some conspicuous deviations from the standard anatomy of foreland fold‐and‐thrust belts. Large basement inliers crop out at a very short distance of less than 50 km behind the southeastern front of the fold belt, reminiscent of Windriver‐style basement uplifts. In contrast to the Rocky Mountain foreland, however, the Anti‐Atlas basement uplifts punctuate tightly folded Paleozoic cover series similar in tectonic style to the Appalachian Valley and Ridge province. Cover shortening is exclusively accommodated by buckle folding, and the Anti‐Atlas fold belt lacks any evidence for duplexing or thrust faults other than the occasional steep reverse fault found near basement inliers. Basement domes have classically been considered as the result of vertical tectonics in a horst and graben fashion, or, alternatively, as large “plis de fond” [Argand, 1924], basement folds. Unfolding of a large portion of an Ordovician quartzite marker bed reveals a minimum shortening of 17% (30 km). Balancing this section at the crustal scale indicates a lower crustal detachment level at 18 to 25 km depth. Basement shortening is inferred to be accommodated through massive inversion of former extensional faults, inherited from a Late Proterozoic‐Lower Cambrian rifting phase.

The Anti-Atlas belt of Morocco is a Variscan chain which appears as a huge anticlinorium oriented NE-SW. In the internal part of this structure, the actual relief shows the basement cropping out as inliers (Piqué 2001) or boutonnières. The cover, a thick pile of Paleozoic sediments up to 12 km thick, is gently folded and of low grade metamorphism in its lower level. The lack of major décollement, of a deformation front or thrust-fault makes the Anti-Atlas an unusual type of belt, which does not fit with classic schemes. The Anti-Atlas has been considered to be a thick skinned fold belt, with the crystalline basement involved in the horizontal shortening and where the folding of the cover fits to a "buckle fold" mode . This structural style is determined by two key parameters: the total thickness of Paleozoic cover series and the relative abundance of shale vs. competent marker beds.The Eastern Anti-Atlas has particular features which are not found elsewhere in the Anti-Atlas. Its location at the intersection between the NW-SE Ougarta chain and the ENE-WSW main body of the Anti-Atlas, produces an egg-box interference pattern. The significance of minor folds and thrusts in the competent beds and their particular orientation is examined. The fact that the cover in the Eastern Anti-Atlas is only 6 km thick, which changes the shale vs competent beds ratio, influences its structural style. The feature that distinguishes the most Eastern Anti-Atlas is the presence of large E-W normal faults affecting the whole structure and creating extensional fault-related folding in the cover. IntroductionThe Moroccan Anti-Atlas belt (Choubert & Faure-Muret 1971) (Fig. 1) is located along the northern border of the WestAfrican Craton (WAC), between the Tindouf Paleozoic basin to the South and the High Atlas to the North. The latter results from a Cenozoic inversion of a Mesozoic basin (Frizon de Lamotte et al. 2000). Laterally limited by the Atlantic Ocean to the South-West, the Anti-Atlas s.s. disappears eastward below an Upper Cretaceous-Cenozoic plateau (the so-called "Hamada du Guir") in the Tafilalt region (Fig. 2). The Anti-Atlas possibly corresponds to a Paleozoic foreland fold-belt, which can be regarded as the deformed foreland of the Variscan chain present in Morocco in the "Moroccan Meseta" (Hoepffner et al. 2006;Raddi et al. 2007) (Fig. 1). According to Helg et al. (2004 and Burkhard et al. (2006), the Anti-Atlas should be regarded as an unusual type of fold belt due to a generalized thick-skinned style and an abundance of weak layers in the Paleozoic sedimentary pile. The particular interest of the Eastern Anti-Atlas is its location at the intersection between the NW-SE Ougarta chain (Haddoum et al. 2001) and the ENE-WSW main body of the Anti-Atlas (Fig. 1). The aim of this study is, on the one hand, to analyse the structural pattern resulting from this interference and, on the other hand, to discuss the age and tectonic significance of large E-W normal faults, which are described here for the first time.Detaile...