Modelo geofísico de contacto entre el Orógeno Pampeano y el Cratón del Río de La Plata en las provincias de Córdoba y Santiago del Estero.

GEOPHYSICAL MODEL OF CONTACT BETWEEN THE PAMPEAN OROGEN AND THE RIO DE LA PLATA CRATON IN PROVINCES OF CORDOBA AND SANTIAGO DEL ESTERO.- In order to better understand the model of contact between Rio de la Plata craton (CRP) and the Pampean Orogen (OP) three gravity profiles, east-west oriented, were performed at 29o 20'S, 32o 30'S and 33° 20'S, corresponding to the latitude of the localities of Sumampa (Santiago del Estero province), Sierra de las Penas and southern end of the Sierra de Comechingones, Cordoba province. The obtained results point to a strong correlation between the new sections and the one at 31°S (profile Jesus Maria) made earlier. On that base a new geophysical model of contact was established between the CRP and the OP for a sector east of the Sierras de Cordoba and Santiago del Estero province, from 29° S to 33° 20'S and 62o to 65 o W, in which the following geotectonic units were recognized: the CRP, as a massive block with an average density of 2.83 g/cm 3 ; the OP, formed by a Cambrian magmatic arc (AMC) to the east, that includes a monzogranite-granodiorite association of type I and metamorphic units that form the accretionary prism (PAC) to the west of the arc, containing an association of peraluminous granites. In addition to geophysical profiles the OP have a base of exhaustive geological knowledge in the study area, contained in detailed surveys. The new profiles reached the western sector of Cordoba, in the province of San Luis, containing Ordovician metamorphic complexes (CMF). As a result it can be said that the contact between the CRP and the OP to the latitude of the Sierras Pampeanas de Cordoba have an elliptical shape located approximately 63o 30'W, under the Chaco-Pampean plain. The contact between the two units would be shaped as a tectonic sliver with subvertical arrangement along the entire thickness of the crust and have a width estimate of 20 km. Structural evidence described in the area of Sierra Norte and Sierra de Sumampa have defined important shears zones within Cambrian granites (525 Ma) that could be linked at the time of the coupling between the CRP and the OP. The current gravimetric surface pattern of the Rio de la Plata craton, in the area immediately to the east of the Sierras Pampeanas of Cordoba and Santiago del Estero province, is an evidence of the dismemberment that occurred since the Upper Paleozoic tectonics and Cretaceous rifting, subsequently reactivated during the Andico tertiary compressional cycle. Seismic studies show that under the plain of Cordoba province, between 64° W and the Parana River at 60o W, the surface of the craton has steep slopes, with blocks of north-south orientation, in similarity with the tectonic style of the Sierras Pampeanas outcropping to the west.