ZusammenfassungDer Saghro reprfisentiert den n6rdlichen Zweig der panafrikanischen Kette im 6stlichen Teil des marokkanischen Anti-Atlas. Die pr~ikambrischen Serien bestehen weitgehend aus vulkanischem und vulkano-detritischem Material, die Zeugnis einer vorwiegend explosiven Vulkantfitigkeit sind. Diese Serien sind intrudiert yon Dioriten und Graniten. Die Altersbestimmung dieser Serien ist problematisch, und ihre Einstufung ist in vorliegender Arbeit revidiert auf Grund struktureller Beobachtungen und Rb-Sr Alter der intrusiven Quarzdiorite von 754 bis 722 Ma. Damit geh6ren die penetrativ deformierten Serien dem unteren PII an und dem oberen PII werden die etwas deformierten Teile des ehemaligen unteren PIII zugeordnet. Nur diejenigen Formationen, die ein charkteristisches Basiskonglomerat oder eine Winkeldiskordanz tiberlagern, werden als PIII eingestuft.Die Hauptschieferung streicht NE-SW, und wird von einem System konjugierter Scherzonen durchschnitten. Im Saghro k6nnen alle Strukturen dieser panafrikanischen Hauptphase durch eine NW-SE gerichtete Einengung erklfirt werden. Die Injektion yon Gfingen und die Kinematik entlang St6rungen im spfiteren Stadium der panafrikanischen Deformation dagegen deutet auf eine NE-SW-Einengung.Der explosive Vulkanismus und die kalk-alkalinen Plutone des Saghro k/3nnen durch einen Inselbogenmagmatismus im Zusammenhang mit der nordvergenten Subduktion entlang des >,accident majeur<< von Bou Azzer -E1 Graara erkl~irt werden . Seine Aktivit~t war gleichzeitig mit den die Subduktion und die Kollision begleitenden Deformationen. AbstractThe Saghro hills constitute the northern branch of the Panafrican mobile belt in the eastern part of the Moroccan Anti-Atlas. The Precambrian terranes are predominantly composed of volcaniclastic and volcanic series witnessing a mainly explosive volcanism, intruded by diorites and granites. Their age attribution is problematic, and has been reconsidered in the present study based on structural evidence and Rb/Sr data of quartzdiorites: penetratively deformed volcano-sedimentaries intruded by these plutons aged between 754 and 722 Ma are now considered as Lower Precambrian II. The Upper PII series have been reattributed, and only formations overlying a basal conglomerate and angular disconformity are considered PIII.Main schistosities are predominantly NE-SW, cut by conjugate sets of strike-slip shear zones. In the Saghro area NW-SE compression can explain the observed structures during this main Panafrican deformation phase, while fault kinematics and dike emplacement related to late deformation events indicate rather a NE-SW compression. The explosive volcanism of the Saghro area can be related to a volcanic arc, active during the subduction-and collision-related Panafrican deformations. This arc would be located on the upper plate in respect to the northward dipping subduction zone evidenced in Bou Azzer -E1 Graara inlier (SAQUAQUE et al., 1989a). R6sum6Les boutonnihres du Saghro constituent la branche nord de la zone panafricaine mobile dans la ...

International audienceIn the southern Moroccan Atlas, abundant volcanic and sedimentary formations, dated from the Ediacaran to Cambrian time, were set at the northwestern Paleo-Gondwanan margin, after the main Pan-African orogenic event. The Precambrian-Cambrian geodynamic transition is characterized by an Early Cambrian marine transgression. We examine the tectonic conditions of this transgression and the magmatic signatures of the volcanic rocks that were produced just before and around the Precambrian-Cambrian boundary. Significant angular unconformities are evidenced, between the Late Neoproterozoic formations and the Cambrian deposits, in the central and eastern Anti-Atlas, which are due to a late Ediacaran NNE-SSW compressional event. The Late Neoproterozoic formations are related to an intracontinental volcanic chain of andesitic to rhyolitic lavas dated to the Ediacaran period. These calc-alkaline rocks were generated by melting of the mantle, previously metasomatized during the Pan-African orogenic stage, and of continental crust. The Late Ediacaran to Early Cambrian formations are analyzed in the Agoundis-Ounein and Toubkal areas, southwest of the old block of High-Atlas. An important basaltic pile unconformably overlies the Ediacaran rhyolitic formation and is overlain by Tommotian sediments. These basalts are continental tholeiites generated by melting of a normal subcontinental mantle. They outpoured from an important N 30°-trending fissural system over a basin floor. Some lherzolite fragments have been sliced along southwest-northeast faults, in the Lower Cambrian sediments. They originated from a transitional mantle between continental and oceanic domains. Farther east of the central Anti-Atlas, the Tommotian Djbel Boho volcano exhibits olivine basalts having an intraplate enriched asthenospheric signature type of ocean island basalt. The magmatic characteristics of the Late Ediacaran to Early Cambrian volcanic rocks, the structural features, and the presence of lherzolite fragments are consistent with a volcanic passive margin rift setting in a WNW-ESE extension regime. The meaning of this extensional event is discussed in relationships to the opening of a Cambrian basin and the drifting of the Avalonian terranes

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