Regeneration after fire in the Monte tropical dry forest, northwest Argentina

Los bosques tropicales secos representan el 42% de la superficie de bosques tropicales y están fuertemente presionados por actividades humanas. Los disturbios antropogénicos redujeron la superficie de bosques de Prosopis en el Monte. Considerando su nivel de degradación, el proceso de regeneración es esencial para su mantenimiento a largo plazo. El fuego es el disturbio másimportante en estos bosques, pero el conocimiento de la dinámica de la vegetación post-fuego es limitado en el norte del Monte. En este trabajo se analizaron tres ambientes: bosque intacto, bosque quemado no inundado y bosque quemado inundado. Se analizó la riqueza y la estructura del sotobosque. Las estrategias de regeneración de las principales especies arbóreas (Prosopisspp. y Geoffroea decorticans) se estudiaron registrando: tipo de estrategia (año 2008), variación temporal en el establecimiento de regeneración por semillas (período 2008-2010), altura alcanzada por las plántulas establecidas a partir de semillas. La riqueza fue mayor y la estructura más compleja bajo la influencia del fuego e inundaciones. Las principales estrategias de regeneración fueron rebrotes de yemas basales para Prosopis sp. y de raíz para G. decorticans. El número de individuos establecidos a partir de semillas fue más del doble a los dos años de la primera medición, mientras que la altura fue influenciada por la disponibilidad de agua. Se concluyó que la recuperación del bosque está fuertemente condicionada por la naturaleza y el tiempo de ocurrencia de los disturbios. El manejo de los rebrotes puede ayudar a que alcancen más altura favoreciendo cambios en la composición y estructura del sotobosque. El control del pastoreo es importante para proteger la regeneración por semillas asegurando una alta diversidad genética.The tropical dry forest represents 42% of the global surface of tropical forest, but these unique ecosystems are under strong pressure of human activities. Anthropogenic disturbances resulted in a dramatic reduction of the extent of Prosopis forests in the Monte region (Argentina). Considering its degree of degradation, forest regeneration is essential for the long term maintenance of this system. The most important disturbance in these forests is fire, but the knowledge about post-fire vegetation dynamics is limited in the north of the Monte. We analyzed three co-existing forest conditions: intact forest, burned non-flooded forest, and burned flooded forest. The species richness and structure of the vegetation was analyzed. The regeneration strategies of the two main forest tree species (Prosopis spp. and Geoffroea decorticans) were analyzed recording the strategy type (year 2008), the temporal variation in seedling establishment (period 2008-2010), and height growth of the seedlings. The richness and understory structure were highly influenced by fire and floodings. The main strategies for regeneration were base sprout and root sprouts for Prosopis and G. decorticans, respectively. The number of seedlings was more than two times higher after two years from the first measurement, while the height growth seemed strongly influenced by water availability. We concluded that the recovery of the forest is influenced by the nature and timing of the disturbances. It is likely that the two disturbed environments will gradually evolve and ultimately show more similarities with the intact forest. However, the management of sprouts can help the sprouts to reach a considerable height in favor of shifts in the understory structure and composition. The control of grazing is important to protect the seedlings and ensure a high genetic variability.Fil: Carón, María Mercedes. University of Ghent; Bélgica. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Dalmasso, Antonio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Ortin Vujovich, Adriana Elizabeth. Universidad Nacional de Salta; ArgentinaFil: Verheyen, Kris. University of Ghent; Bélgic

Seismic velocities in outcropping units in the western flank of the la Invernada range, San Juan Precordillera

En este trabajo se muestran determinaciones de velocidades de ondas sísmicas P (Vp) en un sector (Reserva Don Carmelo) del flanco occidental de la sierra de la Invernada, Departamento Ullúm, Provincia de San Juan. Las velocidades obtenidas con el método de refracción sísmica indican valores de Vp de 550; 1.670 y 4.134 m/s y espesores de 1 m y 7 m aproximadamente, para un modelo de dos capas apoyadas sobre un substrato correspondiente a la mayor velocidad. Las unidades aflorantes reconocidas abarcan grauvacas y areniscas muy bien compactadas que se correlacionan con los valores más altos de Vp determinados en el experimento geofísico para los niveles interpretados a mayor profundidad. Asimismo los valores más bajos de Vp son consistentes con material de tipo aluvional situado en las capas sísmicas más superficiales (< 7m de profundidad). Otras unidades relevadas en el terreno indican afloramientos de diabasas y gabros, los cuales no han sido explorados geofísicamente. Sin embargo, a partir de la comparación de las litologías y velocidades sísmicas Vp observadas con bases de datos globales, es posible predecir la continuación en profundidad de las litologías máficas con velocidades sísmicas de Vp aún mayores que aquellas determinadas en superficie. Estos resultados son de interés debido a que ayudan a identificar una posible faja ofiolítica en Precordillera, en un sector donde el espesor cortical actual estimado en 64 km aproximadamente, estaría engrosado.P-wave seismic velocity (Vp) determinations are shown in this work for a region in the western flank (Don Carmelo nature reserve) of the la Invernada range in the Ullúm Department of the San Juan Province. The velocities obtained using the seismic refraction method indicate Vp values of 550; 1.670 and 4.134 m/s and thicknesses of 1 m and 7 m approximately, for a two-layer over a higher Vp half space model. The exposed units show greywacke and well compacted sandstones, which have a good correlation with the deepest and higher Vp values of the seismic model. Also the lowest Vp values are consistent with alluvial material located in the shallower seismic layers (< 7m depth). Other units observed on the surface exhibit outcrops of diabases and gabros, which were not geophysically explored. However, a comparison between the observed lithologies and Vp values with a global database predicts the continuation at depth of mafic rocks associated with even higher Vp values than those determined at the surface. These results are of interest because they help us to identify an ophiolite belt in the Precordillera, a region presently characterized by an overthickened crust of 64 km.Fil: Perez Lujan, Sofia Beatriz. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Alvarado, Patricia Monica. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Güel, Arturo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Saez, Mauro. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Vujovich, Graciela Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Laboratorio de Tectónica Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentin

Top-down structures of mafic enclaves within the Valle Fértil magmatic complex (Early Ordovician, San Juan, Argentina)

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fértil calc-alkaline igneous complex, Argentina. Excepcional outcrops with vertical walls of more than 300 m high allow us the study of three-dimensional geometries of individual blobs of mafic magma as well as the geometry of pipe-like structures in which mafic microgranular enclaves are concentrated in more than 50 times the normal abundance in the granodiorite mass. The shape of enclaves and pipe-like structures are interpreted as the ressult of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures are the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. They may account for most of the structures found in microgranular enclaves and magma mingling zones that characterize calc-alkaline batholiths. Synplutonic intrusions from the top is the only plausible mechanism to account for the observed structures. The model may be of general application to calc-alkaline batholiths characterized by the presence of mafic microgranular enclaves. An implication of these reverselly stratified magma chambers is the presence of a petrological inversion which may be the consequence of cold diapirs emplaced below the mantle wedge in a suprasubduction setting

Geochemistry of Precordillera serpentinites, western Argentina : evidence for multistage hydrothermal alteration and tectonic implications for the Neoproterozoic-early Paleozoic

Serpentinites are a powerful tool to evaluate mantle composition and subsequent alteration processes during their tectonic emplacement. Exposures of this type of rocks can be found in the Argentine Precordillera (Cuyania terrane) and Frontal Cordillera, both located in central-western Argentina, within the Central Andes. In these regions a Neoproterozoic to Devonian mafic-ultramafic belt composed of serpentinites, metabasaltic dikes/sills, pillow lavas (with an Enriched to Normal Mid-Ocean Ridge Basalts (E- to N-MORB) geochemical signature) and mafic granulites crop out, spatially associated with marine metasedimentary rocks. The serpentinite bodies consist of lizardite/chrysotile+brucite+magnetite, with scarce pentlandite and anhedral reddish-brown Cr-spinel (picotite, pleonaste and spinel sensu stricto) as relict magmatic phases. The original peridotites were moderately-depleted harzburgites (ultramafic cumulates) with an intermediate chemical signature between a mid-ocean ridge and an arc-related ophiolite. Whole-rock Rare Earth Elements (REE) patterns of serpentinites exhibit enriched REE patterns ((La/Yb)CN=13-59) regarding CI chondrite with positive Eu anomalies. These features are the result of an interaction between hydrothermal fluid and serpentinites, in which moderate temperature (350º-400ºC), CO2-rich, mildly basic hydrothermal fluid was involved and was responsible for the addition of Ca, Sr and REE to serpentinites. The presence of listvenites (silica-carbonate rocks) in the serpentinite margins allow us to infer another fluid metasomatism, where lowtemperatures (<250ºC), highly-oxidized, highly-acid fluid lead to the precipitation of silica. The association of these metasomatized serpentinite bodies with neoproterozoic continental margin sucessions and MORB magmatism at the suture zone of the Cuyania and Chilenia terranes suggests the development of an oceanic basin between them during the Neoproterozoic-early Paleozoic

Characterization of ultramafic, mafic and metasedimentary rocks of the Cordón del Peñasco, western Precordillera, Mendoza

En el cordón del Peñasco, ubicado en el sector norte de la provincia de Mendoza, dentro del ámbito de la Precordillera occidental, afloran metasedimentitas en contacto tectónico con una asociación máfica-ultramáfica. Dentro de las metasedimentitas en facies esquitos verdes se han reconocido dos asociaciones: metalimolitas carbonáticas y metaareniscas y metapelitas. Las rocas máficas-ultramáficas están representadas por serpentinitas derivadas de harzburgitas y dunitas, gabros bandeados metamorfizados en facies granulita; diabasas constituyendo diques o filones capa, metabasaltos amigdaloides y metahialoclastitas con bajo grado de metamorfismo. Se realizaron estimaciones termométricas en una granulita máfica (gabro bandeado) utilizando el par granate-clinopiroxeno, obteniéndose temperaturas de 884°C. Las mismas permiten estimar que estos cuerpos experimentaron metamorfismo de alta temperatura, para posteriormente retrogradar a facies de esquistos verdes, sobre la base de aspectos mineralógicos y texturales. Con respecto a las unidades metasedimentarias, el paleoambiente inferido para la unidad de metaareniscas y metapelitas corresponde a pie de talud continental con predominio de sedimentación turbidítica sobre la base de estructuras sedimentarias reconocidas. Mientras que la unidad de metalimolitas carbonáticas pertenecerían a un ambiente marino profundo. Estas unidades han sido asignadas al Eopaleozoico a partir de criterios estratigráficos y deformadas y metamorfizadas hacia fines del Devónico como consecuencia de la Orogenia Chánica.In Cordón del Peñasco area, located in northern Mendoza province, western Precordillera, metasedimentites are in tectonic contact with a mafic-ultramafic association. The former have been under greenschist facies metamorphism and two associations have been recognized: carbonate metasiltstones and metasandstones and metapelites. The mafic-ultramafic association is represented by serpentinized peridotites derived from dunites and harzburgites, layered gabbros in granulite facies; diabase dikes or sills, amigdaloid metabasalts and metahialoclastic rocks with low grade metamorphism. In this contribution, we have estimated metamorphic temperatures on a mafic granulite (layered gabbro) based on garnet-clinopyroxene, obtaining a temperature of 884ºC. This suggests that these bodies have been under high temperature metamorphism and were later retrogressed to greenschist facies, evidenced by mineralogical and textural aspects. Regarding the metasedimentary units, the paleoenvironment of the metasandstones and metapelites association corresponds to a continental slope with turbiditic sedimentation, as suggested by sedimentary structures. The carbonate metasiltstone unit belongs to a deep marine environment. These units have been assigned to Eopaleozoic times based on stratigraphic criteria and deformed and metamorphosed in late Devonian as a consequence of Chanica orogeny.Fil: Boedo, Florencia Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Barredo, Silvia. Universidad de Buenos Aires; Argentin

Structural Evolution of a Composite Middle to Lower Crustal Section: The Sierra de Pie de Palo, Northwest Argentina

The Sierra de Pie de Palo of northwest Argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during Ordovician accretion of the Precordillera terrane to the Gondwana margin. New structural, petrologic, and geochronologic data from a 40 km structural transect reveals that the Sierra de Pie de Palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence. Top-to-the-west thrusting occurred intermittently on discrete ductile shear zones from ∼515 to ∼417 Ma and generally propagated toward the foreland with progressive deformation. Ordovician crustal shortening and peak metamorphic temperatures in the central portion of the Sierra de Pie de Palo were synchronous with retro-arc shortening and magmatic flare-up within the Famatina arc. Accretion of the Precordillera terrane resulted in the end of arc flare-up and the onset of synconvergent extension by ∼439 Ma. Continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the Precordillera terrane. The results support models of Cordilleran orogens that link voluminous arc magmatism to periods of regional shortening. The deformation, metamorphic, and magmatic history within the Sierra de Pie de Palo is consistent with models placing the region adjacent to the Famatina margin in the middle Cambrian and not as basement to the Precordillera terrane

The Late Neoproterozoic-Early Paleozoic basin of the western Argentine Precordillera: Insights from zircon U-Pb geochronology

In central-western Argentina, a belt including marine metasedimentary rocks and mafic-ultramafic bodies occurs throughout the western margin of the Precordillera. The belt is considered as the suture zone between the poorly known Chilenia terrane and the Cuyania terrane, part of the composite West Gondwana margin. It is assigned to the Late Neoproterozoic-Early Devonian based on fossil fauna and radiometric ages. In the southern sector of this belt, in the Peñasco area, two units crop out. The Peñasco Formation comprises metasandstone and metapelite spatially associated with mafic metavolcanic and metahyaloclastic rocks. Metagabbro bodies intrude the succession. The Garganta del León Formation consists of metasandstone and scarce metapelite where tractive and deformational sedimentary structures are preserved. Both units are affected by low-grade metamorphism, but the main foliation S1 and crenulation cleavage S2 are better developed in the Peñasco Formation rocks. U-Pb data on detrital zircon of two metasandstone samples from these units show a dominant detrital input from sources with 1.0–1.3 and 0.65–0.53 Ga ages. Detritus may come from reworked sedimentary units or from igneous/metamorphic complexes from the Cuyania terrane basement that was possibly exhumed in the Ocloyic orogen. A Gondwanan provenance for the Late Neoproterozoic-Cambrian population would also be plausible. A ca. 460 Ma zircon population in the Garganta del León Formation is interpreted to be derived from the Famatinian Arc. This would imply that the deposition of the sediment occurred after the collision of the Cuyania terrane against West Gondwana, and that the Ocloyic orogen acted as a barrier for detritus from the Famatinian Arc and other rocks further east.Fil: Boedo, Florencia Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Vujovich, Graciela Irene. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Martins Pimentel, Márcio. Universidade do Brasília; BrasilFil: Ariza, Juan Pablo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Barredo, Silvia Patricia. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin

U-Pb SHRIMP zircon dating of Grenvillian metamorphism in Western Sierras Pampeanas (Argentina) : correlation with the Arequipa-Antofalla craton and constraints on the extent of the Precordillera Terrane

The Sierras Pampeanas of Argentina, the largest outcrop of pre-Andean crystalline basement in southern South America, resulted from plate interactions along the proto-Andean margin of Gondwana, from as early as Mesoproterozoic to Late Paleozoic times (e.g., Ramos, 2004, and references therein). Two discrete Paleozoic orogenic belts have been recognized: the Early Cambrian Pampean belt in the eastern sierras, and the Ordovician Famatinian belt, which partially overprints it to the west (e.g., Rapela et al., 1998). In the Western Sierras Pampeanas, Mesoproterozoic igneous rocks (ca. 1.0–1.2 Ga) have been recognized in the Sierra de Pie de Palo (Fig. 1) (McDonough et al., 1993 M.R. McDonough, V.A. Ramos, C.E. Isachsen, S.A. Bowring and G.I. Vujovich, Edades preliminares de circones del basamento de la Sierra de Pie de Palo, Sierras Pampeanas occidentales de San Juán: sus implicancias para el supercontinente proterozoico de Rodinia, 12° Cong. Geol. Argentino, Actas vol. 3 (1993), pp. 340–342.McDonough et al., 1993, Pankhurst and Rapela, 1998 and Vujovich et al., 2004) that are time-coincident with the Grenvillian orogeny of eastern and northeastern North America (e.g., Rivers, 1997 and Corrievau and van Breemen, 2000). These Grenvillian-age rocks have been considered to be the easternmost exposure of basement to the Precordillera Terrane, a supposed Laurentian continental block accreted to Gondwana during the Famatinian orogeny (Thomas and Astini, 2003, and references therein). However, the boundaries of this Grenvillian belt are still poorly defined, and its alleged allochthoneity has been challenged (Galindo et al., 2004). Moreover, most of the Grenvillian ages so far determined relate to igneous protoliths, and there is no conclusive evidence for a Grenvillian orogenic belt, other than inferred from petrographic evidence alone (Casquet et al., 2001). We provide here the first evidence, based on U–Pb SHRIMP zircon dating at Sierra de Maz, for a Grenville-age granulite facies metamorphism, leading to the conclusion that a continuous mobile belt existed throughout the proto-Andean margin of Gondwana in Grenvillian times

Top-down structures of mafic enclaves within the Valle Fértil magmatic complex (Early Ordovician, San Juan, Argentina)

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fértil calc-alkaline igneous complex, Argentina. Excepcional outcrops with vertical walls of more than 300 m high allow us the study of three-dimensional geometries of individual blobs of mafic magma as well as the geometry of pipe-like structures in which mafic microgranular enclaves are concentrated in more than 50 times the normal abundance in the granodiorite mass. The shape of enclaves and pipe-like structures are interpreted as the ressult of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures are the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. They may account for most of the structures found in microgranular enclaves and magma mingling zones that characterize calc-alkaline batholiths. Synplutonic intrusions from the top is the only plausible mechanism to account for the observed structures. The model may be of general application to calc-alkaline batholiths characterized by the presence of mafic microgranular enclaves. An implication of these reverselly stratified magma chambers is the presence of a petrological inversion which may be the consequence of cold diapirs emplaced below the mantle wedge in a suprasubduction setting

Sedimentary provenance analysis of the Early Paleozoic units of the arroyo El Leoncito area, Southern Precordillera, province of San Juan

En el área del arroyo El Leoncito, en el ámbito de la Precordillera Sur, afloran la Formación Cabeceras y el Grupo Ciénaga del Medio. Ambas unidades consisten en sucesiones silicoclásticas marinas asociadas espacialmente a rocas máficas toleíticas depositadas en un margen continental sometido a extensión, el cual se desarrolló durante el Ordovícico-Devónico a lo largo del margen occidental del terreno Cuyania previo a la colisión del terreno Chilenia. A fines de caracterizar este ambiente y sus áreas de aporte, este trabajo presenta un análisis de procedencia sedimentaria mediante conteo modal de componentes de metareniscas de la Formación Cabeceras, Grupo Ciénaga del Medio y otras unidades de la Precordillera Sur (formaciones Portezuelo del Tontal, Peñasco, Garganta del León y Sandalio). Las modas analizadas sugieren que las rocas que actuaron como fuente fueron principalmente metamorfitas de bajo grado y sedimentitas. En menor proporción, participaron rocas ígneas de composición intermedia-ácida y/o rocas metamórficas de grado medio a alto. El aporte de rocas volcánicas fue subordinado. Los diagramas de discriminación señalan a un orógeno reciclado como la principal zona de aporte, con participación de una zona de arco disectado. Estos resultados pueden explicarse en un contexto donde el orógeno Oclóyico habría actuado como área de aporte y, a la vez, como barrera orográfica ante el transporte de material desde el este (arco Famatiniano y áreas cratónicas). La proveniencia de detritos desde el oeste no es totalmente descartada. La similitud de las modas analizadas sugiere que no hubo cambios significativos en las áreas de aporte para el segmento de la Precordillera analizado (31°45´S-32°15´S) durante el período Ordovícico-Devónico.In the Arroyo El Leoncito area, northern sector of the Southern Precordillera, the Cabeceras Formation and Ciénaga del Medio Group crop out. These units consist of marine siliciclastic successions and tholeiitic mafic rocks developed on a continental margin during the Ordovician-Devonian. In order to characterize this setting and its source areas, this work presents a sedimentary provenance analysis using modal composition of metasandstones of the Cabeceras Formation and Ciénaga del Medio Group, as well as other units of the Southern Precordillera (Portezuelo del Tontal, Peñasco, Garganta del León and Sandalio formations). Analyzed detrital modes suggest that mainly low-grade metamorphic and sedimentary rocks acted as source. To a lesser extent, intermediate-acid igneous rocks and/or medium- to high-grade metamorphic rocks of similar composition also participated. The contribution of volcanic rocks was subordinated. Discrimination diagrams indicate a recycled orogen as the main provenance zone, with the participation of a dissected arc zone. These results can be explained in a context where the Ocloyic orogen would have acted as source and, at the same time, as a barrier that prevented the transport of detritus from regions located further east (i.e. Famatinian arc and/or cratonic areas). Detritus provenance from the west is not totally ruled out. The similarity of the detrital modes of the formations involved in the analyzed segment of the Southern Precordillera (31°45'-32°15'S) suggests that there were no significant changes in source areas during the Ordovician-Devonian.Fil: Giunta, Agostina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Schmidt, Daniela Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Boedo, Florencia Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentin