1,721,026 research outputs found
Successive reactivation of older structures under variable heat flow conditions evidenced by K-Ar fault gouge dating in Sierra de Ambato, northern Argentine broken foreland
Get PDFThe Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of N-S reverse faults that disrupted a W-E Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477-470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the K-Ar dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 °C). K-Ar ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (~360-220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ~360 Ma and a last clay minerals forming event at ~220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (~360-311 Ma for 2-1 μm grain size fraction, ~326-286 Ma for 1-0.2 μm and ~291-219 Ma of <0.2 μm), we modeled discrete deformation events at ~417 Ma (ending of the Famatinian cycle), ~317-326 Ma (end of Gondwanic orogeny), and ~194-279 Ma (Early Permian - Jurassic deformation). According to our data, the Neogene reactivation would not have affected the K-Ar system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.Fil: Nobile, Julieta. 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; ArgentinaFil: 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; ArgentinaFil: 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; ArgentinaFil: 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; ArgentinaFil: Wemmer, Klaus. Universität Göttingen; Alemani
Dynamic topography in South America
Get PDFSupracrustal tectonics and mantle flow interact to create Earth's topography. While tectonics is associated with the isostatic components of topography, the deflections caused by mantle dynamics, or dynamic topography, represent the non-isostatic components. South America is an ideal natural laboratory to analyze these two contrasting components from the high Andes to the distal plains. Both regions are active and affected by complex geodynamic processes like the subduction of oceanic ridges, geometry and age of slabs, etc. These subducting anomalies affect not only the convergence dynamics and stresses along the entire margin, but also the distribution of mass anomalies in the mantle, which are the main cause of sublithospheric flow and dynamic topography. Here we revisited five examples from north to south, which demonstrate that, the Andes and the distal forelands have been uncompensated since the beginning of the Cenozoic and that additional forces, such as mantle downwellings and upwellings, are required to account for the observed topographies in basins and elevations.Fil: Davila, Federico Miguel. University College London; Estados Unidos. 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; ArgentinaFil: Lithgow Bertelloni, Carolina. University College London; Estados Unido
Reply to comment on “dynamic topography in South America” by Hechenleitnera, Fiorelli, Larrovere, Grellet-Tinnera, and Carignano
Get PDFThis is a Reply to Hechenleitner and collaborators Comment, who proposed a Cretaceous age for the whole Llanos Formation (central Argentina, Sierras Pampeanas Province), based on neosauropod fossils, instead of Miocene as originally proposed by Ezpeleta et al. (2006) and Dávila et al. (2007). However, redbeds that underlay the thick paleosoils of the Llanos Formation provided nine detrital U-Pb Paleogene (62 Ma, earliest Cenozoic) ages on zircon grains (Astini et al., 2009; Ezpeleta 2009). On the base of this evidence, and other mammal remnant within the Sierras Pampeanas (where the Llanos Formation develops), we proposed this is a condensed unit with Mesozoic ages at the bottom and Mio-Pliocene (likely younger) to the top.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; ArgentinaFil: Lithgow Bertellonib, Carolina. University College London; Estados Unido
Heat flow and lithospheric thickness analysis in the Patagonian asthenospheric windows, southern South America
Get PDFThe lithosphere–asthenosphere boundary (LAB) is a first-order discontinuity, essential to understand the Earth composition and evolution. However, its detection has been critical and several regions still lack of coverage. Southern Patagonia, in southern most South America, is one such area, which has been affected by the subduction of a seismic oceanic ridge (South Chile Ridge) and formation of an extensive slab window since ~12 Ma. We calculate the LAB position by defining the thermal lithospheric thickness of the southernmost Patagonia using the thermal conductivity equation to estimate the surface heat flow. We used data from seventy-five hydrocarbon wells of two from the most productive petroleum basins in Argentina: the Golfo de San Jorge and Magallanes-Austral basins. Our results show the highest heat flow values in the southernmost region, over the Austral basin and core of the slab window (~70–90 mW/m2). These values are twice as hot as global average. To the north, over de Golfo de San Jorge basin and northern margin of the slab window, heat flows are “normal” (~50–60 mW/m2). These thermal contrasts, from south to north, agree with the kinematic reconstructions of the Chile ridge and northward widening of the slab window. These heat flows values evidence an attenuated lithospheres, which thickens eastward from between 25 km (to the west, trench region) to 50 km (to the east, foreland region).Fil: Avila, Pilar. 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; ArgentinaFil: 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; Argentin
Thermochronology in South America
No full textThermochronology and geochronology share many theoretical and technical fundamentals (e.g., Reiners et al., 2005; Braun et al., 2006, among others) and both essentially provide time information, yet they pursue different questions, given the low temperature sensitivity of thermochronometers. While thermochronology is aimed at understanding rates of processes, geochronology, focuses on the calculation of absolute ages. Since the early developments of thermochronology in the 1960’, and the pioneer studies in the 1980’-90’, medium- and low-temperature thermochronology has became a powerful technique in geodynamic and tectonic studies in different settings. More recently, Its uses have broadened to other fields like geomorphology and stratigraphy,as well as mining and oil exploration, as closure temperatures of many mineral systems overlap with the temperature window of epithermal mineral deposits and of source rock maturation for petroleum formation. In South America, low-temperature thermochronometry has been instrumental for understanding the age and mode of Andean construction and to infer its triggering mechanisms, to understand the exhumation associated with opening of the Atlantic and the subsequent evolution of the passive margins, and to focus petroleum exploration, among others. The main objective of this Special Issue “Thermochronology in South America: From Cordilleras to cratons” is to visualize the thermochronology community working in this part of the planet, its current developments regarding new analytical and numerical modelling laboratories, new analytical developments, and novel applications in various mineral systems for geodynamics and applied geological problems.Fil: Parra, Mauricio. Universidade de Sao Paulo; BrasilFil: 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; Argentin
Dynamics of deformation and sedimentation in the northern Sierras pampeanas: An integrated study of the neogene Fiambalá basin, NW argentina: Comment and discussion
Get PDFIn a recent contribution to the Geological Society of America Bulletin, Carrapa et al. (2008) provided an interesting geochronological and thermoChronological database for the Fiambalá Basin, northern end of the Sierras Pampeanas, which, together with stratigraphic, sedimentological and structural data, led them to interpret a late Miocene–Pliocene foreland reorganization from a simple scenario (e.g., DeCelles and Giles, 1996) to settings dominated by intermontane basement thrusting. They associated this reorganization with the beginning of fl at subduction, which would have been coeval (according to Carrapa et al., 2008) with broken foreland stages in the Bermejo Basin (>400 km south). One of the most crucial issues that Carrapa et al. (2008, p. 1518–1543) address (in their words) is “the structural and sedimentary behavior of broken forelands and their relationships with large-scale plate-tectonic processes such as fl at-slab subduction” that can “contribute to a better understanding of the transition from unbroken foreland (thin-skinned) to broken foreland (thick-skinned) styles of deformation and related sedimentation.” However, for some reason, they did not discuss the entire Andean stratigraphy of the area, superbly exposed much less than 50 km southward and 100 km northward of their study region (in central Famatina and Southern Puna, respectively; see Fig. 1). These two regions are evidently much closer than the Bermejo Basin exposures (see Jordan et al., 2001), which were used as a key correlation. The Bermejo Basin is located at ~31°S, i.e., ~400 km southward of Fiambalá (Fig. 1). Although I do agree that the entire extent of the Sierras Pampeanas shows evidences of basement- thrusting tectonics during the late Miocene to Pliocene and even during the Quater nary (already demonstrated previously; e.g., Jordan and Allmendinger, 1986; Ramos et al., 2002; among others), there are sources that indicate the foreland partitioning would have begun earlier. Particularly, I disagree with: (1) the timing of transformation from “simple fl exural stages” to “broken foreland scenarios” and (2) their interpretation about a synchronous slab shallowing at ca. 6 Ma. This discussion is divided into four lines of reasoning: mapping and stratigraphy of Tertiary sequences in Famatina and Southern Puna; timing of basement thrusting in boundary regions; thermochronology; and evidences of flat subduction between 29°S and 26°S.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; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
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