1,721,018 research outputs found
Light hydrocarbon speciation as a powerful tool to define physico-chemical features of geothermal systems: an example from El Tatio geothermal field (Northern Chile)
No full textThe Calama-Olacapato-El Toro fault system in the Puna Plateau, Central Andes: Geodynamic implications and stratovolcanoes emplacement
No full text""The structural evolution of the Puna Plateau is characterized by the activity of both orogen-parallel and orogen-oblique faults. Understanding the possible relationship between these two structural styles, their geodynamic implications and the influence on the migration of magmas is important to get insights into the tectonic and magmatic evolution of the Central Andes. In this study, we present a structural analysis of the orogen-oblique Calama-Olacapato-El Toro fault system and the surrounding orogen-parallel thrust faults in the central-eastern Puna Plateau. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of the tectonic features in the studied area. We propose a three-dimensional geometrical reconstruction of the main fault planes showing their attitude and intersections at depth. The study indicates that the crust underwent simultaneous deformation along both the vertical transcurrent Calama-Olacapato-El Toro fault system and the low-angle thrust faults, and that the back-arc portion of the Calama-Olacapato-El Toro fault system developed as a transfer zone among the main N-striking thrusts. Our model considers that both orogen-parallel and orogen-oblique fault systems should be regarded as parts of the same tectonic system, accommodating crustal shortening of a thickened crust. The study suggests that the tectonic control on the magma and fluid circulation in the crust is mainly related to the geometry of the fault planes and the orientation of the stress field, with a previously unrecognized important role played by the orogen-parallel thrust faults on the emplacement of the stratovolcanoes. (C) 2013 Elsevier B.V. All rights reserved."
Columnar jointing in vapor phase altered Cerro Galan Ignimbrite, Paycuqui, Argentina
No full textAbstract Columnar jointing is thought to occur primarily
in lavas and welded pyroclastic flow deposits. However, the
non-welded Cerro Galán Ignimbrite at Paycuqui, Argentina,
contains well-developed columnar joints that are instead
due to high-temperature vapor-phase alteration of the
deposit, where devitrification and vapor-phase crystalliza-
tion have increased the density and cohesion of the upper
half of the section. Thermal remanent magnetization
analyses of entrained lithic clasts indicate high emplace-
ment temperatures, above 630°C, but the lack of welding
textures indicates temperatures below the glass transition
temperature. In order to remain below the glass transition at
630°C, the minimum cooling rate prior to deposition was
3.0 10–8.5 102°C/min (depending on the experimental
data used for comparison). Alternatively, if the deposit was
emplaced above the glass transition temperature, conduc-
tive cooling alone was insufficient to prevent welding.
Crack patterns (average, 4.5 sides to each polygon) and
column diameters (average, 75 cm) are consistent with
relatively rapid cooling, where advective heat loss due to
vapor fluxing increases cooling over simple conductive
heat transfer. The presence of regularly spaced, complex
radiating joint patterns is consistent with fumarolic gas rise,
where volatiles originated in the valley-confined drainage
system below. Joint spacing is a proxy for cooling rates and
is controlled by depositional thickness/valley width. We
suggest that the formation of joints in high-temperature,
non-welded deposits is aided by the presence of underlying
external water, where vapor transfer causes crystallization
in pore spaces, densifies the deposit, and helps prevent
welding
Structural control on geothermal circulation in the Cerro Tuzgle–Tocomar geothermal volcanic area (Puna plateau, Argentina)
No full text""The reconstruction of the stratigraphical–structural framework and the hydrogeology of geothermal areas is. fundamental for understanding the relationships between cap rocks, reservoir and circulation of geothermal. fluids and for planning the exploitation of the field. The Cerro Tuzgle–Tocomar geothermal volcanic area. (Puna plateau, Central Andes, NW Argentina) has a high geothermal potential. It is crossed by the active. NW–SE trans-Andean tectonic lineament known as the Calama–Olacapato–Toro (COT) fault system, which. favours a high secondary permeability testified by the presence of numerous springs.. This study presents new stratigraphic and hydrogeological data on the geothermal field, together with the. analysis from remote sensed image analysis of morphostructural evidences associated with the structural. framework and active tectonics.. Our data suggest that the main geothermal reservoir is located within or below the Pre-Palaeozoic–Ordovician. basement units, characterised by unevenly distributed secondary permeability. The reservoir is recharged by. infiltration in the ridges above 4500 m a.s.l., where basement rocks are in outcrop. Below 4500 m a.s.l., the. reservoir is covered by the low permeable Miocene–Quaternary units that allow a poor circulation of shallow. groundwater. Geothermal fluids upwell in areas with more intense fracturing, especially where main regional. structures, particularly NW–SE COT-parallel lineaments, intersect with secondary structures, such as at the. Tocomar field. Away from the main tectonic features, such as at the Cerro Tuzgle field, the less developed network. of faults and fractures allows only a moderate upwelling of geothermal fluids and a mixing between hot. and shallow cold waters.. The integration of field-based and remote-sensing analyses at the Cerro Tuzgle–Tocomar area proved to be. effective in approaching the prospection of remote geothermal fields, and in defining the conceptual model. for geothermal circulation."
High temperature emplacement of the Cerro Galán and Toconquis Group ignimbrites (Puna plateau, NW Argentina) determined by TRM analyses.
No full textEstimates of pyroclastic flow emplacement. temperatures in the Cerro Galán ignimbrite and Toconquis. Group ignimbrites were determined using thermal. remanent magnetization of lithic clasts embedded within. the deposits. These ignimbrites belong to the Cerro. Galán volcanic system, one of the largest calderas in the. world, in the Puna plateau, NW Argentina. Temperature. estimates for the 2.08-Ma Cerro Galán ignimbrite are. retrieved from 40 sites in 14 localities (176 measured. clasts), distributed at different distances from the caldera. and different stratigraphic heights. Additionally, temperature. estimates were obtained from 27 sample sites (125. measured clasts) from seven ignimbrite units forming. the older Toconquis Group (5.60–4.51 Ma), mainly. outcropping along a type section at Rio Las Pitas, Vega. Real Grande. The paleomagnetic data obtained by. progressive thermal demagnetization show that the clasts. of the Cerro Galán ignimbrite have one single magnetic. component, oriented close to the expected geomagnetic. field at the time of emplacement. Results show therefore. that most of the clasts acquired a new magnetization. oriented parallel to the magnetic field at the moment of. the ignimbrite deposition, suggesting that the clasts were. heated up to or above the highest blocking temperature. (Tb) of the magnetic minerals (Tb=580°C for magnetite;. Tb=600–630°C for hematite). We obtained similar emplacement. temperature estimations for six out of the seven. volcanic units belonging to the Toconquis Group, with the. exception of one unit (Lower Merihuaca), where we found. two distinct magnetic components. The estimation of. emplacement temperatures in this latter case is constrained. at 580–610°C, which are lower than the other ignimbrites.. These estimations are also in agreement with the lowest. pre-eruptive magma temperatures calculated for the. same unit (i.e., 790°C; hornblende–plagioclase thermometer;. Folkes et al. 2011b). We conclude that the Cerro Galán. ignimbrite and Toconquis Group ignimbrites were emplaced. at temperatures equal to or higher than 620°C, except for. Lower Merihuaca unit emplaced at lower temperatures. The. homogeneity of high temperatures from proximal to distal. facies in the Cerro Galán ignimbrite provides constraints for. the emplacement model, marked by a relatively low eruption. column, low levels of turbulence, air entrainment, surface–. water interaction, and a high level of topographic confinement,. all ensuring minimal heat loss
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
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
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