Resumen
The Andean Paleozoic basement of the Cordón del Plata (Argentina) consists of two sets of rocks showingdifferent 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 metamorphicconditions and related to the Chanic orogenic event of the Famatinian Orogenic Cycle (Upper Devonian-LowerCarboniferous). The Vallecitos beds is pre-orogenic to the Chanic deformation event and must have been deposited in afore-arc basin located on the active margin of Chilenia, before its collision with the passive margin of Gondwana. Theupper set unconformably rests on the Vallecitos beds and consists of the Late Carboniferous El Plata Formation, andthe Río Blanco Conglomerates, probably Late Carboniferous-Permian in age. These rocks have been affected by eastdirectedthrusts and associated folds formed under very low-grade to non-metamorphic conditions. This deformationcan be related to the San Rafael phase (Gondwanan Orogen). The El Plata Formation was deposited in an extensionalback-arc basin while the Río Blanco conglomerates must have been deposited in a retro-arc basin, both of them on theactive margin of Gondwana. The Choiyoi Group, essentially volcanic and Permo-Triasic in age, rests unconformably onthe previously described successions and was deposited in an extensional setting (pre-orogenic stage) associated withthe beginning of the Andean Cycle. This cycle lead to the uplift of the Frontal Cordillera during the Cenozoic and thedeposition of thick continental units at the base of the Cordón del Plata in Neogene-Quaternary times.