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This study is focused on the analyses of a Chaschuil section (27° 49′ S–68° 04′ W), north of the Argentina Famatina Belt, where Ordovician explosive-effusive arc volcanism took place under subaerial to subaqueous marine conditions. In analyzing the profile, we have recognized an Arenigian succession composed by dominant volcaniclastic lithofacies represented by volcaniclastic debris flow, turbidity current and minor resedimented syn-eruptive pyroclastic depositsand lavas. The upper portions of succession are represented by volcanogenic sedimentary lithofacies with fossiliferous levels. Great volumes of the volcaniclastic deposits are strongly controlled in their transport by mass flow processes. These representative deposits provide significant data in relation to the coeval volcanic events for recognizing a continuous explosive volcanism together a minor effusive activity and the degradation of volcanic edifices. Likewise mass flow deposits give indications of the high rate of sedimentation, strong slope control and instability episodes in the basin, typical of those volcanic environments. That substantial information was the key to understand the features and evolution of the Arenigian basin in the north of the Famatina System. Fil: Cisterna, Clara Eugenia. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Coira, Beatriz Lidia Luisa. Universidad Nacional de Jujuy; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The Macon granitoids are part of a tonalite/diorite granodiorite suit. Their trace elements place these rocks in the volcanic arc field. They have distribution patterns similar to those observed for rocks from Choschas, Taca Taca, Chuculaqui, and Quebrada de Batin. Macon rocks show strong enrichment of elements such as K, Rb, Th, and light REEs, which suggests crustal participation associated with the arc source. 87Sr/86Sri and (143Nd/144Nd)i isotopic ratios of two samples are compatible with arc-related rocks. Their calculated age of 482.7 Ma is consistent with other ages determined for the Ordovician western Puna eruptive belt (Faja Eruptiva de la Puna Occidental). This belt is made up of a set of granitoids, characteristic of the northern part of the Puna of Catamarca that, together with similar exposures of Salta and the Chilean region near the border with Argentina, suggests a meridian strike. The Ordovician ages and arc characteristics of the Sierra de Macon rocks, at the eastern extreme of the belt, incorporate them into this igneous province. This significantly increases the width of the Sierra de Macon igneous province to as much as 150 km at this latitude. Fil: Poma, Stella Maris. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Quenardelle, Sonia Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Litvak, Vanesa Dafne. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Maisonnave, Emma Beatriz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina Fil: Koukharsky, Magdalena Maria L.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The basement of the Central Andes located in central-western Argentina (31º20′S - 69º22′W) is composed by the Cuyania and Chilenia terranes which were amalgamated to Gondwana in the Early-Mid Paleozoic. Between the Precordillera (Cuyania) and Frontal Cordillera (Chilenia) there are exposures of marine metasedimentary rocks associated with mafic rocks with an E-MORB chemical signature that represent the remnants of an extensional basin developed between both terranes. The stratigraphic features and the distribution of the Early-Mid Paleozoic units along the Western Precordillera were constrained by remote sensing techniques. This allowed us to identify two stages in the evolution of the sedimentary in-fill of the marine basin: an initial stage (Mid-Late Ordovician) marked by widespread extensional tectonics and a finning-upwards sequence interbedded with volcanic-plutonic mafic rocks; and a Late Ordovician?-Devonian where the sedimentation was characterized by the development of coarsening-upwards sequences with low participation of mafic rocks. Flattened parallel folds associated with pre-Andean thrusts have locally a top-to-the SW vergence. These pre-Andean (Late Devonian) structures are the relics of the Chanic orogen whose double vergence is the result of the control exerted by previous structures related to the ordovician rifting. This is constrained by the residual and regional magnetic anomalies which reflect an important correlation between deep and surface structures. We propose the inception of a subduction zone with an eastward polarity on the proto-Pacific margin of Gondwana as the responsible for the compressive geotectonic framework that led to the closure of the Western Precordillera basin during the Late Devonian and the development of the Chanic thick-skinned-dominated orogen. Fil: Ariza, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina 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"; Argentina Fil: Sanchez, Marcos Ariel. 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; Argentina Fil: Christiansen, Rodolfo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina Fil: 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; Argentina Fil: 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 Fil: Martínez, Myriam Patricia. 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; Argentina

In the Famatina range, Sierras Pampeanas of Argentina (SW Gondwana), subvertical calc-alkaline lamprophyric dike swarms crop out through >300 km. The dikes cut Ordovician units with a prominent NW-SE trending and are covered by continental sedimentary successions of Pennsylvanian to Permian age. The dikes show a strong structural control associated with Riedel fault systems. Detailed field analysis suggested a ∼N-S opening direction oblique to the attitude of dike walls and a left-lateral transtensional tectonics during the emplacement. 40Ar/39Ar geochronology of a lamprophyric sample defined a crystallization age (plateau; whole rock) of 357.1 ± 7.1 Ma (MSWD = 2.3). Coetaneous ductile zones with dominant strike-slip motion, documented along western Argentina for >600 km, suggest a regional event in SW Gondwana during the Mississippian. We propose that this deformation was the result of the counterclockwise fast rotation of Gondwana between 365 and 345 Ma, when the Famatina range and western Argentina occupied a sub-polar position. A transform margin along SW Gondwana better explains our (and others) data rather than a subduction margin. This scenario is also consistent with the occurrence of A-type granites and normal-fault basins within the foreland as well as bimodal volcanics. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Canelo, Horacio Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Davila, Federico Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: de Hollanda, María Helena M.. Universidade de Sao Paulo; Brasil Fil: Teixeira, Wilson. Universidade de Sao Paulo; Brasil

Foreland basin systems are intimately linked to thrust belts and activation and reactivation of structures in association with convergent plate dynamics, capable of controlling regional uplifts, sedimentation, as well as drainage patterns among other processes. The Ischigualasto-Villa Unión basin (IVB) is a Miocene broken foreland, occurring in-between the Famatina-Sañogasta, Valle Fértil and Maz Ranges in the Western Sierras Pampeanas, Argentina, Central Andes. We conducted U–Pb geochronology by SHRIMP in igneous zircons and LA-ICPMS in detrital zircons as well as whole rock Sm–Nd analyses in the Quebrada del Médano and Desencuentro Formations – the uppermost units of the IVB. The new and compiled data provide new insights on the influence of flat-slab on the uplift of the Sierras Pampeanas and Precordillera and consequent shift of the drainage patterns in the basin infill. The SHRIMP age for the youngest zircons from a volcanic tuff of the middle portion of the Desencuentro Formation yielded a mean 206Pb/238U age of 8.49 ± 0.33 Ma whereas the other grains gave concordant ages from 10 to 1433 Ma. The detrital zircon ages from both Formations indicated that different sourced materials contributed to the basin infill, through time and space. The major age modes in the detrital populations were: 1) 1250-950 Ma, (2) 850-600 Ma, (3) 540-500 Ma, (4) 490-460 Ma, (5) 350-320 Ma, (6) 300-250, (7) 40 Ma and (8) 16-8 Ma. From a statistical point of view, we defined two similar aged groups with distinct major contribution provenance: a first cluster with main Cambrian-Ordovician ages and a second one with main Permian and Mesoproterozoic ages. The bulk picture suggests a critical change in the IVB provenance history since the mid-late Miocene, roughly consistent with the Pampean flat-slab subduction model that controls uplifts of the Western and Eastern Sierras Pampeanas and associated regional drainage shifts in Central Andes, as like geodynamic processes in Western North America. We interpret the statistic change in the distribution of the IVB zircons as product of: (1) the presence of axial rivers flowing parallel to the basement arches in the more distal foreland; (2) a disconnection between the IVB and the Bermejo basin related to the uplift of the IVB western margin; (3) the uprising of the IVB eastern ranges. Our findings are also consistent with the acquired TDM ages (1.2–0.9 Ga) and the coupled εNd(t) constraints (−6 to −5) for samples collected along the stratigraphy of both IVB Formations that indicated recycled Grenville-aged sources were likely overload by sourced rocks with high lithologic erodibility. Fil: Lemos Santos, Daniel. Universidade de Sao Paulo; Brasil Fil: Teixeira, Wilson. Universidade de Sao Paulo; Brasil Fil: Collo, Gilda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Canelo, Horacio Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

As a result of new studies carried out in the offshore of Perú during the exploration and hydrocarbon evaluation of the forearc basins, new U–Pb SHRIMP and TIMS in zircons and some Ar–Ar data were obtained in the metamorphic and igneous basement. The understanding of this basement was critical to evaluate different hypotheses that have been proposed for the tectonic evolution of pre-Andean crust of Perú. Recent research performed in the basement rocks of the Marañón Massif in northern Perú, claimed that west of this area was a basement-free region in the Paleozoic, where the arc and forearc were developed in a mafic quasi-oceanic crust. However, petrographic studies and new preliminary ages indicate, for the first time, the nature and age of this sialic basement. Reconnaissance studies were performed in several offshore islands, as the Las Hormigas de Afuera Island west of Lima, and Macabí and Lobera islands along the edge of the continental platform. These data were complemented with the studies of some cutting samples obtained in recent exploration wells in northern Perú. The results of the present work show two large crustal domains in the Peruvian offshore forearc. A northern domain contains late Paleozoic igneous rocks that appear to be the southern offshore continuation of the Amotape–Tahuin block, which is interpreted as the southernmost remnant of the Laurentia Alleghenian orogen. The central offshore domain, known as the Paracas High, corresponds to the outer shelf high of previous studies. It contains orthogneisses of Grenville-age, probably recrystallized during an Ordovician magmatic episode. The new results show that the central offshore of Perú is an extension of the Grenville-age basement affected by Famatinian, early Paleozoic magmatism, well exposed in the southern domain in the Arequipa Massif along the coast of southern Perú. Fil: Romero, Darwin. Savia Peru S.A; Perú Fil: Valencia, Kiko. Savia Peru S.A; Perú Fil: Alarcón, Pedro. Savia Peru S.A; Perú Fil: Peña, Daniel. Savia Peru S.A; Perú Fil: Ramos, Victor A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires; Argentina