EVOLUTION OF THE SIERRAS-DE-CORDOBA, ARGENTINA

Located in the southeastern part of the Sierras Pampeanas (Argentina), the Pampean Ranges of Cordoba show the evolution at the western margi n of the Rio de la Plata craton, from extensional stages during Neopro terozoic times to compressive stages during the Pampean orogeny. The C umbre de Gaspar Group represents distal deep-sea clastic sedimentation deposited in a passive margin environment, very possibly during a tim e of incipient oceanization. The Santa Sabina Group, representing shel f sedimentation, rests conformably on the Cumbre de Gaspar Group. Stoc ks of granites and granodiorites of calc-alkaline affinity intruded th e Cumbre de Gaspar Group during the early Pampean or earlier. The poly phase Pampean orogeny involves several distinct metamorphic and orogen ic events. Metamorphism is discussed using the chemical composition of minerals. The major effect of the Pampean orogeny was the formation o f a pile of westward thrust blocks. The Rio de la Plata craton, thrust above its marginal basin, forms the uppermost unit. The intrusion of the El Pilon granite (dated at 520 +/- 5 Ma) post-dates these tectonic and metamorphic events. After this main orogenic event, the domain re mained permanently located on the cratonic side of younger Famatinian and Andean orogenic events. The Mermela Group probably corresponds to the molasse of the Pampean orogeny and to the base of a new sedimentar y cycle. It is difficult to distinguish Famatinian tectonics in the Si erras de Cordoba because the main orogeny occurred further west. Howev er, this orogenic cycle is marked by the intrusion of the large Achala batholith. During the late Palaeozoic and Mesozoic the Sierras de Cor doba remained a stable platform. The whole region was rejuvenated by t he Andean orogeny, which induced tilted blocks in its foreland and the Pocho volcanics of shoshonitic affinities.