RIASSUNTO Evoluzione tettonica delle unità Dorsale Calcaire, Pre-Dorsalian e Massylian nell'area di Chefchaouen (Rif settentrionale, Marocco) In questo lavoro è presentata l'analisi strutturale delle successioni bacinali e di piattaforma calcarea affioranti nell’area di Chefchaouen (Rif settentrionale). L'analisi ha permesso la ricostruzione della storia tettonica delle successioni studiate, caratterizzata dalla sovrapposizione di più fasi deformative. Le prime due fasi sono associate al sovrascorrimento, vergente a SW, della Dorsale Calcaire sulle unità Pre-Dorsalian e Massylian, registrata come deformazione progressiva nelle successioni poste a letto. La terza fase è contraddistinta da un raccorciamento diretto NW-SE, mentre le ultime due fasi sono caratterizzate da faglie trascorrenti e normali che deformano l'intera pila tettonica. KEY WORDS: deformation, Flysch Basin, folding, structural analysis, thrusting INTRODUCTION The analyzed area, located close to the Chefchaouen village in the western Rif Chain (northern Morocco), is characterized by the tectonic superposition of the Dorsale Calcaire Unit onto basin successions of the Pre-Dorsalian and Massylian units ( e.g. DE CAPOA et alii, 2004; ZAGHLOUL et alii, 2003). Such a superposition occurs along a ca. 90 km long thrust segment running from Sebta to Chefchaouen (this being separated from an eastern segment by the Jebha transfer fault). STRUCTURAL ANALYSIS Hanging-wall carbonates of the Dorsale Calcaire Unit form a large, SW verging ramp anticline with associated parasitic folds. Pre-buckle thrusts also occur as well as a disjunctive, spaced cleavage. Theoretical fold π-axis calculated form stereographic projections of poles to bedding, meso-scale fold hinges, pre-buckle thrusts and meso-scale thrusts are all compatible with ENE-WSW shortening. Intense deformation characterizes the pre-Dorsalian succession located in the footwall, with a marked strain gradient toward the tectonic contact. The latter is accompanied by a few hundreds of meters-thick deformation zone including both ductile and brittle structures. D1 early structures consist of macro- to meso-scale, close isoclinal to close folds with associated, in pelitic levels, a rare crenulation cleavage and a crenulation lineation. These structures are deformed by mainly SE verging, D2-related thrust faults. Both carbonates and argillites along the regional tectonic contact are cut by late, SW dipping shear bands. Generally the whole Pre-Dorsalian succession is affected by D2-related, late, extensional shear planes orthogonal to the tectonic transport. A strong boudinage produced in several zones, the total bedding disruption, giving often to the whole succession the characters of a tectonic mélange. Subsequent shortening is recorded by D 3 -related, mainly NW verging thrust faults with associated S-C structures. The Massylian succession, located in the footwall to the pre- Dorsalian Unit, is characterized by superposed deformation with an intensity increasing toward the tectonic contact. The first deformation phase (D 1 ) produced tight to isoclinal folds accompanied by a pervasive axial plane cleavage in pelitic rocks and a spaced convergent foliation in the more competent layers. Parasitic folds are common, as well as thrust faults and pre-buckle thrusts affecting competent layers embedded in pelites. Frequent high-deformation zones, especially where pelites are dominant, show isoclinal (D 1 ) intrafolial folds and an associated severe boudinage that, similarly to the Pre- Dorsalian succession, locally produced a tectonic mélange. The subsequent deformation stage (D 2 ) is recorded by open to close Tectonic evolution of the Dorsale Calcaire, Pre-Dorsalian and Massylian units in the Chefchaouen area (Northern Rif, Morocco) FRANCESCO D'ASSISI TRAMPARULO (*), BILAL EL OUARAGLI (**), STEFANO VITALE (*) & NAJIB MOHAMMED ZAGHLOUL (**) Fig. 1 –Panoramic view of Chefchouaen area. _________________________ (*) Dipartimento di Scienze della Terra, Università di Napoli Federico II, Largo San Marcellino 10, 80138, Napoli. (**) Department of Earth Sciences, F.S.T.-Tangier, University of Abdelmalek Essaadi, Morocco Rend. online Soc. Geol. It., Vol. 22 (2012), pp. 223-224, 1 figg. © Società Geologica Italiana, Roma 2012 223