Resumen
RESUMEN. Se presenta un estudio del basamento cristalino integrado por las Metamorfitas Cushamen, los Granitoides Mamil Choique y una serie granitica postectonica, representantes de un ciclo mayor tecto-termico que evoluciono entre el Paleozoico Inferior y el Superior en un ambiente hercinotipico colisional. En el se emplazaron diques alcalinos carboniferos (330 Ma), que se interpretan como senalando una etapa de 'rift' desarrollada sobre el cinturon orogenico estabilizado. Un ciclo magmatico posterior (280 Ma) dio lugar al desarrollo de plutonitas y volcanitas probablemente a traves de una tectonica de intraplaca vinculada a transcurrencia y extension cortical. En este complejo igneo-metamorfico, durante el Jurasico, intruyen stocks de granitoides (171 Ma) y un pluton de gabro olivinico (170 Ma). Las metamorfitas y migmatitas (488 Ma), que son el resultado de un episodio principal metamorfico de grado medio a alto, localmente compatible con anatexis, derivaron de grauwacas y pelitas con intercalaciones de areniscas cuarzosas y margas. Las rocas muestran la superposicion de tres fases de deformacion orientadas =D1:N90°/30°S, D2:N331°/70°E y D3:N49°/28°S. Estas direcciones, en especial la segunda, controlaron la tectonica post-carbonifera de fracturacion (principalmente transcurrente) en bloques que caracteriza la region. La quimica de los granitoides del basamento los caracteriza como calcoalcalinos, per a metaaluminosos y de altos valores 87Sr/86Sr inicial, situacion que permite interpretar a la mayoria de ellos como anatecticos de tipo S. Posteriormente se emplazan cuerpos menores de granitoides postectonicos (344-348 Ma) en un ambiente epicortical y asociados a hidrotermalismo, marcando un levantamiento del orogeno que, hacia el este y noreste generaria las cuencas de Sierra Grande y Ventana. Finalmente, se destacan las caracteristicas mas sobresalientes del Macizo Norpatagonico y las Sierras Pampeanas, concluyendo que, debido a las similitudes que presentan, es posible proponer la presencia de un unico orogeno central paleozoico, difiriendo en consecuencia con la hipotesis de la aloctonia de Patagonia. ABSTRACT. The Cushamen Metamorphites, the Mamil Choique Granitoids and a postectonica granite suite are presented as the main units of the crystalline basement of the region, which evolved during the Lower to Upper Paleozoic in a Hercynotype colisional environment. Some minor carboniferous (330 Ma) alkaline dykes point out a rifting stage of a stabilized orogenic belt. Later on, during the Permian (280 Ma), a new magmatic event took place probably related to extension and transcurrent fracturing in an intraplate setting. In this igneous-metamorphic complex some Jurassic (171 Ma) granitoid stocks and olivine bearing gabbros (171 Ma) were emplaced. The 488 Ma old metamorphites and migmatites resulted from a main medium to high grade tecto-thermal event that produced local anatexis from a protolith of graywackes, pelites and some quartz-rich sandstones and marls. These show three main deformational episodes with trends =D1:N90°/30°S, D2:N331°/70°E and D3:N49°/28°S, which controlled the post-carboniferous fracturing tectonics mainly developed through transcurrent faulting that originated a horst-graben structure in the region. The chemistry of the oldest granitoids indicates that they are mostly calc-alkaline, per to metaaluminous, with high 87Sr/86Sr initial ratios S type anatectic rocks, as well as the postectonic (344-348 Ma) ones which were intruded simultaneously with hidrothermalism in an epicortical zone of the orogenic belt, during and after an important uplift that originated, towards the east and northeast the Sierra Grande and Ventana paleozoic basins. The most outstanding common features of the North Patagonian Massif and the Pampean Ranges are pointed out, concluding that it is possible to define a single paleozoic orogenic belt, incompatible with the hypothesis of the pre-Permian allochthonous Patagonia.