The Basement of the Andean Frontal Cordillera in the Cordón del Plata (Mendoza, Argentina): Geodynamic Evolution El Basamento de la Cordillera Frontal de los Andes en el Cordón del Plata (Mendoza, Argentina): Evolución Geodinámica

The Andean Paleozoic basement of the Cordón del Plata (Argentina) consists of two sets of rocks showing different stratigraphy, structure and metamorphism. The lower one is represented by the pre-Carboniferous (Devonian?) Vallecitos beds. These rocks have been affected by folds and associated cleavage, developed under low-grade metamor-phic conditions and related to the Chanic orogenic event of the Famatinian Orogenic Cycle (Upper Devonian-Lower Carboniferous). The Vallecitos beds is pre-orogenic to the Chanic deformation event and must have been deposited in a fore-arc basin located on the active margin of Chilenia, before its collision with the passive margin of Gondwana. The upper set unconformably rests on the Vallecitos beds and consists of the Late Carboniferous El Plata Formation, and the Río Blanco Conglomerates, probably Late Carboniferous-Permian in age. These rocks have been affected by east-directed thrusts and associated folds formed under very low-grade to non-metamorphic conditions. This deformation can be related to the San Rafael phase (Gondwanan Orogen). The El Plata Formation was deposited in an extensional back-arc basin while the Río Blanco conglomerates must have been deposited in a retro-arc basin, both of them on the active margin of Gondwana. The Choiyoi Group, essentially volcanic and Permo-Triasic in age, rests unconformably on the previously described successions and was deposited in an extensional setting (pre-orogenic stage) associated with the beginning of the Andean Cycle. This cycle lead to the uplift of the Frontal Cordillera during the Cenozoic and the deposition of thick continental units at the base of the Cordón del Plata in Neogene-Quaternary times. El basamento paleozoico de los Andes, que aflora en el Cordón del Plata (Argentina), está formado por dos conjuntos de rocas con diferente estratigrafía, estructura y metamorfismo. El conjunto inferior está representado por las capas de Vallecitos, de edad precarbonífera (posiblemente devónica). Estas rocas se encuentran afectadas por pliegues y clivajes asociados, formados en condiciones metamórficas de bajo grado y relacionados con la Orogenia Chánica del Ciclo Famatiniano (Devónico Superior-Carbonífero Inferior). Las capas de Vallecitos tienen un carácter preorogénico y se habrían depositado en una cuenca de antearco situada sobre un margen activo de Chilenia, antes de su colisión con el margen pasivo de Gondwana. El conjunto superior, discordante sobre las capas de Valle-citos, está constituido por la Formación El Plata, de edad Carbonífero Superior, y los Conglomera