1,720,969 research outputs found
Rare element minerals’ assemblage in El Quemado pegmatites (Argentina): insights for pegmatite melt evolution from gahnite, columbite-group minerals and tourmaline chemistry and implications for minerogenesis
Full text linkThe pegmatite district of El Quemado (NW Pampean Ranges, NW Argentina) hosts several Ordovician pegmatite bodies of theLCT (Li, Cs, Ta) type. We present paragenetic assemblages for a set of samples from two of the El Quemado pegmatite groups,Santa Elena and Tres Tetas, and mineral chemistry analyses for gahnite, columbite-group minerals, tourmaline, micas, albite,microcline, and discuss the relation between their major element composition and the degree of evolution of pegmatite melts. Thechemical composition of rare element minerals allows recognizing an evolutive trend reaching highly differentiated compositions, with complex paragenetic assemblages including Li-, Zr-, U-, Zn-, P-, Mn- and Ta-bearing minerals. The temperature ofcrystallization during the magmatic phase was below 400 °C. Non-pervasive hydrothermal alteration, testified by a moderatepresence of phyllosilicates, affected the pegmatite bodies. Chlorite geothermometry indicates that the circulation of postmagmatic hydrothermal fluids occurred at a temperature ranging between 200 °C and 250 °C. The mineralogical featuresrecognized in the El Quemado pegmatite rocks have implications for the metallogenesis of the region, suggesting that thepegmatites potentially contributed to the genesis of Ta-Nb oxide placer mineralizations.Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geológicos Andinos; ArgentinaFil: Fulignati, Paolo. Universita Degli Studi Di Pisa. Dipartimento Di Scienze Della Terra; ItaliaFil: Gioncada, Anna. Universita Degli Studi Di Pisa. Dipartimento Di Scienze Della Terra; ItaliaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints
No full textThe Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with εNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana. © 2009 Elsevier Ltd. All rights reserved.Fil: López de Azarevich, Vanina L.. Universidad Nacional de Salta; ArgentinaFil: Escayola, Monica Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentina. Universidad Nacional de Salta; ArgentinaFil: Pimentel, Márcio M.. Universidade do Brasília; BrasilFil: Tassinari, Colombo. Universidade de Sao Paulo; Brasi
Lunar recession encoded in tidal rhythmites: a selective overview with examples from Argentina
Full text linkThe study of tides from the sedimentary record of tidal rhythmites, applying fast Fourier transform analysis, contributes to the understanding of the surficial evolution of our highly dynamic planet, and of the astronomical cycles that influenced the ancient tidal systems. This overview of lunar retreat rates, which includes examples from Argentina, displays a generalized pattern of nonlinear, progressively extended lunar cycles up to the present day. The lunar retreat calculated at different stages of the Earth’s history identifies three time spans of extremely high recession rates, amounting to almost twice that of the present day: Archean–Paleoproterozoic (6.93 cm/year), Neoproterozoic I–Ediacaran (7.01 cm/year) and Ediacaran–early Cambrian (6.48 cm/year). Older comparable recession rates are difficult to recognize because of the lack of tidal rhythmic sequences. The maximum lunar retreat rate is registered after the Copernican meteor bombardment event on the Moon at ~900 Ma, and the time span coincides with the continental dispersal of Rodinia. Every acceleration of the lunar retreat rate coincides with two main processes: (1) meteorite impacts on the Earth or Moon, and (2) reconfiguration of landmasses accompanied by earthquakes that generated changes in the rotational axis of the Earth, inundation surfaces, and glaciation/deglaciation processes. The simultaneous occurrence of such processes makes it difficult to distinguish the causes and effects of each individual process, but its conjunction would have promoted the destabilization of the Earth–Moon system in terms of moment of inertia that was transferred to the Moon rotation.Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentin
Technological applications for Neoproterozoic-Cambrian limestones from northwest Argentina
No full textSome rocks have been used as ornamental stones without knowledge of the natural material or its characteristics when included in agglomerates, or even those acquired during the benefit process. This study shows that prospection of ornamental stones should include studies of physical, chemical and mechanic properties that allow determination of its application to industrial merchant. The Neoproterozoic-Cambrian limestones fron Northwest Argentina extend along a wide area, with interesting sectors of low fracturation, being lack of oxidation and karst morphologies. High compresion and bending strength values of this micrites, good engraved qualities, polish surfaces and cut facilities generate an important industrial interest for exploration and quarry development evaluation at Sierra de Castillejo. Limestones abrasive and weather resistance, along with very fine-grain and porosity reduction due to cementation by the calcite veins framework, make them suitable for covers of high performance furniture and ornamentation in architectural designs. If fractured, they are suitable for paving tiles, sculptures, small ornamental stones, adornments, ordinary jewels, arids and lime formation. Reserves at Sierra de Castillejo are equivalent to 20-year production of the San Juan limestones and 11-year production of the Córdoba marbles.Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentina. Universidad Nacional de Salta; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; ArgentinaFil: Castillo, Alfredo L.. Universidad Nacional de Salta; ArgentinaFil: López, Natalia Cecilia. Universidad Nacional del Sur. Departamento de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Lithium and potassium brine deposits from South America: characterization, hydrochemistry, depocenters and resources
Full text linkLos depósitos de Li y K en salmueras constituyen recursos ácueos caracterizados por una salinidad elevada (> 400% NaCl) y elementos en solución con >350 ppm Li y 0,5-1 % K, acompañados principalmente de Mg, Na, Ca y B. Su génesis está condicionada por la evolución de cuencas endorreicas en clima árido, donde el Li es aportado por lixiviación de rocas circundantes o fuentes termales, y concentrado en los acuíferos por evapotranspiración. En Sudamérica occidental, las condiciones de aridez se desarrollaron a partir del Cretácico, favorecidas por el levantamiento del Altiplano y la Puna y el emplazamiento del arco volcánico andino desde el Mioceno. La configuración de las cuencas corresponde a ante-arco (Atacama) e intra-arco (salares de la Puna), de las cuáles éstas últimas evolucionan a partir de depocentros cretácico-terciarios en Puna Septentrional y como depocentros individuales terciarios en Puna Austral. Los recursos de Li sudamericanos suman el 68% de los mundiales, la producción mundial de LCE es de 82.000 t/a (38% Chile y Argentina), y la capacidad de producción de los salares argentinos es de 400.000 t/a LCE. Este trabajo proporciona una revisión de la evolución de las cuencas salinas desde el límite K-T hasta la actualidad, así como los resultados de la exploración de salmueras de Li y las proyecciones económicas disponibles, en la Puna y el Altiplano.Lithium and K brine deposits constitute water resources characterized by high salinity (> 400% NaCl) and elements in solution in the order of >350 ppm Li and 0.5-1% K, accompanied mainly by Mg, Na, Ca and B. Its genesis is conditioned to the evolution of endorheic basins in arid climates, to which Li is contributed by leaching from surrounding rocks or thermal sources, and concentrated in the aquifers by evapotranspiration. Halite crystallization occurs in the saline nucleus, decreasing the Na+ in solution, enriching itself in Li+ and 7 Li. In western South America, arid conditions developed from the Cretaceous and were enhanced by the uplift of the Altiplano and Puna and the emplacement of the Andean volcanic arc since the Miocene. The basins configuration corresponds to antearc (Atacama) and intra-arc (Puna salars), of which the latter evolve from CretaceousTertiary depocentres in Northern Puna and as individual Tertiary depocentres in Southern Puna. South American Li resources add up to 68% of total resources, global LCE (lithium carbonate equivalent) production is 82,000 t/y (38% Chile and Argentina), and Argentina salars’ production capacity is 400,000 t/y LCE. Lithium is used in the industry of batteries, aluminum and its alloys, glass and ceramics, greases and lubricants, air conditioning, medicine and pharmaceuticals, polymers. Also, 6 Li is used in the production of nuclear energy as a source of tritium, and 7 Li is used as a hydroxide to regulate the pH of the cooling material in the primary circuits of pressurized water nuclear reactors, where it is used as a heat conductor due to its high melting temperature, and as fluoride in molten salt reactors. This paper provides an overall review of salar basins’ evolution from K-T boundary to recent, as well as available Li brine exploration results and economic projections, over the Puna and Altiplano.Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geológicos Andinos; Argentina. Universidad Nacional de Salta. Facultad de Cs.naturales. Carrera de Geología; ArgentinaFil: Schalamuk, Bernardo Isidoro. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Recursos Minerales. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Recursos Minerales; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentin
Alkaline volcanism involved in the rifting process of the pensilvanian basin, Mendoza province
Full text linkLas rocas volcánicas inter-carboníferas de la Cordillera Frontal de Mendoza comprenden la Asociación Volcánica Meso-Varíscica, compuesta por diques (hasta 5 m de espesor) y coladas vesiculares de colores negruzcos. Estratigráficamente son pre-Pensilvaniano. Presentan textura intergranular a intersertal, compuesta por plagioclasa de hasta 2 mm (57%), entre los que se disponen clinopiroxeno (13%), opacos (12%), anfíbol de hasta 1 cm (10%), olivino, ocasionalmente cuarzo, feldespato potásico y epidoto; con apatito de hasta 1 mm como accesorio común. Químicamente son basaltos, traquibasaltos potásicos, mugearitas y hawaiitas, con una tendencia alcalina y afinidad con una suite de tipo Basanita-Fonolita. Registran una cristalización fraccionada de olivinoplagioclasa en los estadios iniciales, y de clinopiroxeno-plagioclasa en estadios más avanzados. Fueron generados en un ambiente tectónico de intraplaca a partir de la fusión parcial de un manto de composición lhertzolítica a harzburgítica, de signatura MORB, modificado por contaminación cortical. La relación K vs K/Th* y la presencia de fases minerales hidratadas, sugieren a su vez un proceso de subducción y procesos de metasomatismo por fluidos asociados a subducción que brindan a estas rocas una firma de arco magmático continental. Su signatura geoquímica es equivalente a los basaltos del Rift Africano, con algunas variaciones similares a las registradas en los diversos brazos de la mega-estructura. Sin embargo, la complejidad de la distribución geoquímica de los elementos genera la necesidad de datos isotópicos que confirmen la interpretación presentada. Este episodio magmático ocurrido bajo un régimen extensional (rifting) marca el inicio de la cuenca marina carbonífera superior de la Formación Alto Tunuyán, es equivalente al registrado en otras localidades a lo largo del eje cordillerano e implica un evento de extensión generalizado en el margen occidental de Gondwana limitado estratigráficamente por la Fase Diastrófica Chánica (Devónico superior) y el arco volcánico Permo-Triásico (Grupo Choiyoi).The inter-Carboniferous volcanic rocks of Frontal Cordillera, Mendoza, are represented by the MesoVariscic Volcanic Association composed by dikes (5 m-thick) and vessiculated lava-flows of black color. They are stratigraphically pre-Pennsylvanian. Develop an intergranular to intersertal texture, composed of 2 mm plagioclase (57%), and in-between clinopyroxene (13%), opaques (12%), 1 cm amphibole (10%), olivine, and occasionally quartz, K-feldspar and epidote; with apatite up to 1 mm as the common accessory. Chemically they are basalts, K-traquibasalts, mugearites and hawaites, with an alkaline trend and Basanite-Phonolite Suite affinities. It registers a fractioned crystallization of olivine-plagioclase in the initial stage and of clinopyroxene-plagioclase in later stages. They were generated in an intraplate tectonic environment from partial melting of mantle of lhertzolite to harzburgite composition, of MORB signature, modified by crustal contamination. K vs K/Th* relation and presence of hydrous mineral fases mineral fases sugest a subduction process and metasomatism by fluids asociated to subduction that brings these rocks a continental magmatic arc signature. The geochemical signature is equivalent to basalts from the African Rift, with some similar variations registered in the diverse arms of the mega-structure. Although, a complex arrangement of geochemical elements make the necessity of isotope studies to confirm the interpretations presented. This magmatic episode occurred during an extensional regime (rifting) marks the initiation of the marine Carboniferous basin of the Alto Tunuyán Formation, and is equivalent to that register in other localities along the Cordillera axis and implies and generalized extensional event in the western margin of Gondwana, limited stratigraphically by the Chanica Diastrofic Fase (Upper Devonian) and the Permo-Triassic volcanic arc (Choiyoi Group).Fil: López, Vanina Lucrecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto Superior de Correlación Geológica. Grupo Vinculado al INSUGEO- Centro de Estudios Geologicos Andinos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; Argentin
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