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This article provides stratigraphic and geochronological data from a central part of Gondwana's northern margin--the Moroccan Meseta Domain. This region, located to the north of the Anti-Atlas area with extensive outcrops of Precambrian and lower Paleozoic rocks, has hitherto not received much attention with regard to its Precambrian geology. Detrital and volcanic zircon ages have been used to constrain sedimentary depositional ages and crustal affinities of sedimentary source rocks in stratigraphic key sections. Based on this, a four-step paleotectonic evolution of the Meseta Domain from the Ediacaran until the Early Ordovician is proposed. This evolution documents the transition from a terrestrial volcanic setting during the Ediacaran to a short-lived carbonate platform setting during the early Cambrian. The latter then evolved into a rifted margin with deposition of thick siliciclastic successions in graben structures during the middle to late Cambrian. The detritus in these basins was of local origin, and a contribution from a broader source area (encompassing parts of the West African Craton) can only be demonstrated for postrifting, i.e., laterally extensive sandstone bodies that seal the former graben. In a broader paleotectonic context, it is suggested that this Cambrian rifting is linked to the opening of the Rheic Ocean, and that several peri-Gondwanan terranes (Meguma and Cadomia-Iberia) may have been close to the Meseta Domain before drifting, albeit some of them seem to have been constituted by a distinctly different basement. L'article présente des données stratigraphiques et géochronologiques sur la partie centrale de la marge septentrionale du Gondwana, le domaine de la Meseta marocaine. Cette région, située dans le nord de la chaîne de l'Anti-Atlas, où affleurent en abondance des roches d'âge précambrien et paléozoïque inférieur, n'a jusqu'à présent pas reçu beaucoup d'attention en ce qui concerne sa géologie précambrienne. Des âges sur zircons détritiques et volcaniques ont été utilisés pour délimiter les âges du dépôt de sédiments et les affinités crustales des sources des sédiments dans des coupes stratigraphiques clés. À la lumière de cette information, une évolution paléotectonique en quatre étapes du domaine mésétien allant de l'Édiacarien à l'Ordovicien précoce est proposée qui documente le passage d'un milieu volcanique terrestre durant l'Édiacarien à un milieu de plateforme carbonatée pendant une courte période durant le Cambrien précoce, qui a ensuite cédé la place à un milieu de marge de divergence où ont été déposées d'épaisses séquences silicoclastiques dans des structures de graben durant le Cambrien moyen à tardif. Les détritus dans ces bassins provenaient de sources locales, et l'apport d'une région source plus large (comprenant des parties du craton ouest-africain) ne peut être démontré que pour la période ayant suivi le rifting, sous forme de corps gréseux de vaste étendue latérale qui scellent les grabens préexistants. Dans un contexte paléotectonique plus large, il est suggéré que ce rifting cambrien est associé à l'ouverture de l'océan Rhéique, et que plusieurs terranes périgondwaniens (Meguma et Cadomia-Iberia) pourraient s'être trouvés à proximité du domaine mésétien avant leur dérive, bien que certains semblent avoir été constitués à partir un socle distinct. [Traduit par la Rédaction], Introduction Shortly after the acceptance of the plate tectonics theory by the majority of geoscientists all over the world, the Canadian geologist Paul E. Schenk published a sweeping and thought-provoking [...]

The present paper reviews Tertiary volcanic and sedimentary formations in the Inter-Andean region of southern Ecuador (between 2 [degrees] S and 4 [degrees] 20'S) in order to develop a geodynamic model of the region. The formations occur in the southern shallow prolongation of the Inter-Andean Valley between the Cordillera Real to the east, and the Cordillera Occidental and Amotape-Tahuin Provinces to the west. One hundred fifty zircon fission-track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions. The Paleogene to early Miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks. In addition, relics of Eocene continental sedimentary series have been identified. The Neogene sedimentary series lie unconformably on deformed and eroded metamorphic, sedimentary and volcanic formations. They were deposited in two stages, which are separated by a major unconformity dated at [approximately equal to] 10-9 Ma. (1) During the middle and early late Miocene ([approximately equal to] 15-10 Ma) marginal marine deltaic, lagoonal, lacustrine and fluvial environments prevailed, which we group under the heading 'Pacific Coastal sequences'. They presumably covered a greater surface area in southern Ecuador than their present occurrence in small topographic depressions. We suggest that they were deposited in the shallow marine Cuenca and Loja Embayments. Deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna. (2) Above the regional (angular) unconformity, the coastal facies are overlain by late Miocene ([approximately equal to] 9-5 Ma) continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material. They represent the 'Intermontane sequences' of the basins of Cuenca, Giron-Santa Isabel, Nabon, Loja and Malacatos-Vilcabamba. Sedimentologic and stratigraphic results are used to discuss the tectonic setting of Neogene sedimentation in the forearc and arc domain of the Ecuadorian subduction system. During the Pacific Coastal stage, northward displacement of the coastal forearc block along the Calacali-Pallatanga fault zone has driven crustal collapse in the Inter-Andean region. As a result, extensional subsidence drove the eastward ingression of shallow seas into the Cuenca and Loja Embayments from the Manabi and Progreso Basins to the west. Tectonic inversion in the forearc area during the early late Miocene (at [approximately equal to] 9.5 Ma) reflects the initiation of W-E oriented compression and uplift in the Inter-Andean region and the establishment of smaller Intermontane stage basins, which host the continental sequences. Coeval topographic rise of the Cordillera Occidental is indicated by the onset of clastic input from the west. The small Intermontane Basin of Nabon ([approximately equal to] 8.5-7.9 Ma) formed during the period of maximum compression. The present data prove that the Neogene Andean forearc and arc area in southern Ecuador was a site of important but variable tectonic activity, which was presumably driven by the collision and coupling of the Carnegie Ridge with the Ecuadorian margin since [approximately equal to] 15-9 Ma. Keywords: sedimentary facies; volcanics; fission-track chronostratigraphy; Neogene tectonics

The use of white phengitic micas with Si=3.3 p.f.u. to indicate Alpine high-pressure metamorphism is insufficient proof for the erosion of high-P metamorphic source rocks. Such a method is questionable because it does not provide buffer documentation and does not accurately establish the polytype of mica. That only locally preserved Variscan basement of the Alps does not contain blueschist relics does not connote that blueschist metamorphism during Variscan convergence did not occur.