Muchos de los episodios de metamorfismo y deformacion asociados a las rocas de bajo grado del NO argentino fueron tradicionalmente vinculados con orogenos antiguos como el pampeano (Cambrico) y el ocloyico (Ordovicico). En el cinturon del Famatina, la falta de dataciones precisas y de un analisis estratigrafico de detalle en las sucesiones con bajo grado, condujeron a interpretaciones ambiguas respecto a la evolucion paleozoica del segmento sur de los Andes Centrales. Estudios recientes establecen que el 'basamento metamorfico' de bajo grado de dicha region estaria conformado por las formaciones Negro Peinado y Achavil, cuyos analisis de procedencia las vinculan con la finalizacion del ciclo pampeano. Por su parte, la Formacion La Aguadita, tambien afectada por metamorfismo de bajo grado, corresponderia a depositos sinorogenicos ordo vicieos (ocloyieos). En consecuencia, el conjunto seria mas joven que la FormacionPunco viscana (prepampeana) con la que fue habitualmente correlacionado. Las edades K-Ar presentadas en este trabajo permiten establecer que el metamorfismo y la deformacion de estas unidades son Ordovicicos y no mas antiguos (Proterozoico-Cambrico Medio) como se interpreto durante muchos años. Edades de 457±9 Ma (roca total) y 463±14 Ma (fraccion <2µm) obtenidas para la Formacion Negro Peinado, permiten su vinculacion con el climax de la orogenia ocloyiea, desarrollada en el margen occidental de Gondwana durante el Paleozoico inferior. Las edades de 435±12 Ma (fraccion <2µm) en la Formacion La Aguadita y de 444±8 Ma (roca total) en filonitas de la faja de deformacion angulos, son consistentes con la extension de este ciclo orogenico hasta el Silurico Inferior. Adicionalmente, se obtuvo una edad de 359±7 Ma (fraccion <2µm) en rocas de la Formacion Negro Peinado (faja de deformacion Las Trancas), que evidencia un reequilibrio local del sistema isotopico K-Ar parcialmente coincidente con el rango temporal asignado para la orogenia achaliana (Silurico Tardio-Carbonifero temprano).ABSTRACT:Many of the metamorphic and deformational events associated to low-grade units in NW Argentina have been linked with ancient orogenies, like the Pampean (Cambrian) and the Ocloyic (Ordovician) cycles. The lack of specific ages in the low-grade metamorphic rocks of the Famatina belt, as well as the absence of a detailed stratigraphic analysis, have led to ambiguous interpretations respect to the Paleozoic evolution of the southern segment of the Central Andes. Recent work allows recognition of two units within the low-grade 'metamorphic basement'; the Negro Peinado and the Achavil formations. Provenance analysis relates deposition of both units to the final stages of the Pampean cycle during the Cambrian, whereas an Ordovician (Ocloyic) synorogenic nature is suggested for the La Aguadita Formation, also traditionally included within the low-grade 'metamorphic basement'. Thus, as a whole, these units areyounger than the traditionally correlated pre-Pampean Punco vise ana Formation. K-Ar ages obtained forFamatina indicate that low-grade metamorphism and deformation of these units are Ordovician, in contrast to a much older age (Proterozoic-Middle Cambrian) previously suggested. Ages of 457±9 Ma (whole rock) and 463±14 Ma (<2µm fraction) for the Negro Peinado Formation allow establishing a link with the climax of the Ocloyic Orogeny developed along western Gondwana during the early Paleozoic. Ages of 435±12 Ma (<2µm fraction) in the La Aguadita Formation and of 444±8 Ma (whole rock) in phyllonites of the angulos shear zone are consistent with an extent into the earliest Silurian for this cycle. Additionally, a 359±7 Ma (<2µm fraction) age for the Negro Peinado Formation (Las Trancas shear zone) indicates local resetting within the age range assigned to the Achalian Orogeny (Late Silurian-early Carboniferous).Many of the metamorphic and deformational events associated to low-grade units in NW Argentina have been linked with ancient orogenies, like the Pampean (Cambrian) and the Ocloyic (Ordovician) cycles. The lack of specific ages in the low-grade metamorphic rocks of the Famatina belt, as well as the absence of a detailed stratigraphic analysis, have led to ambiguous interpretations respect to the Paleozoic evolution of the southern segment of the Central Andes. Recent work allows recognition of two units within the low-grade 'metamorphic basement'; the Negro Peinado and the Achavil formations. Provenance analysis relates deposition of both units to the final stages of the Pampean cycle during the Cambrian, whereas an Ordovician (Ocloyic) synorogenic nature is suggested for the La Aguadita Formation, also traditionally included within the low-grade 'metamorphic basement'. Thus, as a whole, these units areyounger than the traditionally correlated pre-Pampean Punco vise ana Formation. K-Ar ages obtained forFamatina indicate that low-grade metamorphism and deformation of these units are Ordovician, in contrast to a much older age (Proterozoic-Middle Cambrian) previously suggested. Ages of 457±9 Ma (whole rock) and 463±14 Ma (<2μm fraction) for the Negro Peinado Formation allow establishing a link with the climax of the Ocloyic Orogeny developed along western Gondwana during the early Paleozoic. Ages of 435±12 Ma (<2μm fraction) in the La Aguadita Formation and of 444±8 Ma (whole rock) in phyllonites of the Ángulos shear zone are consistent with an extent into the earliest Silurian for this cycle. Additionally, a 359±7 Ma (<2μm fraction) age for the Negro Peinado Formation (Las Trancas shear zone) indicates local resetting within the age range assigned to the Achalian Orogeny (Late Silurian-early Carboniferous).