科研之友
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摘要
The Andean Paleozoic basement of the Cord車n 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 R赤o 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 R赤o 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 Cord車n del Plata in Neogene-Quaternary times. El basamento paleozoico de los Andes, que aflora en el Cord車n del Plata (Argentina), est芍 formado por dos conjuntos de rocas con diferente estratigraf赤a, estructura y metamorfismo. El conjunto inferior est芍 representado por las capas de Vallecitos, de edad precarbon赤fera (posiblemente dev車nica). Estas rocas se encuentran afectadas por pliegues y clivajes asociados, formados en condiciones metam車rficas de bajo grado y relacionados con la Orogenia Ch芍nica del Ciclo Famatiniano (Dev車nico Superior-Carbon赤fero Inferior). Las capas de Vallecitos tienen un car芍cter preorog谷nico y se habr赤an depositado en una cuenca de antearco situada sobre un margen activo de Chilenia, antes de su colisi車n con el margen pasivo de Gondwana. El conjunto superior, discordante sobre las capas de Valle-citos, est芍 constituido por la Formaci車n El Plata, de edad Carbon赤fero Superior, y los Conglomera
