Geoquímica y sistemática isotópica de rocas metamórficas del Paleozoico inferior. Noroeste de Argentina y Norte de Chile (21°-27° S)

Más del 95% de los afloramientos del basamento metamórfico del Paleozoico inferior en el Noroeste de A rgentina y Norte de Chile están compuestos por rocas félsicas. Los contenidos de elementos mayores, trazas y las composiciones isotópicas de Pb, Rb-Sr y Sm-Nd son típicos de las rocas que conforman la corteza superior. Las edades modelos Sm-Nd de las rocas estudiadas son de ca 1.8 Ga. Estas rocas han sido afectadas por un evento principal de metamorfismo del Paleozoico temprano (ca. 500 Ma). Se considera que el reciclado de la corteza, con un importante evento de metamorfismo durante el Paleozoico temprano, es el proceso dominante en la generación de muchos de los magmas con composiciones graníticas originados desde el Paleozoico temprano hasta el Reciente. Las espesas secuencias sedimentarias ordovícicas son derivadas también de esa misma corteza en común. Los xenolitos félsicos de la corteza inferior extraídos por el magmatismo perteneciente al sistema del Rift Salta, son muy similares composicionalmente al basamento del Paleozoico inferior. Se estima que la composición de la corteza desde la parte superior hasta la inferior sería principalmente félsica. Las rocas máficas tienen muy poco volumen y forman principalmente diques. Sus edades modelos Sm-Nd revelan dos grupos, uno con edades de ca 1.8 Ga y otro con edades de ca £ 1.0 Ga No ha sido posible realizar una interpretación ajustada del ambiente geodinámico en donde se ha desarrollado este magmatismo básico.Felsic rocks comprise more than 95% of the outcropping Early Paleozoic metamorphic basement. Their major and trace element contents and Pb, Rb-Sr and Sm-Nd isotope compositions are typical for upper crustal rocks. Sm-Nd model ages are ca 1.8 Ga. The principal ages of high-grade metamorphism is Early Paleozoic (ca 500 Ma). Recycling of this crust is the dominating process in the formation of granitoid magmatic rocks from Early Paleozoic to Recent. Ordovician sediments are also derivates of this crust. Felsic lower crustal xenoliths from the Salta Rift system are compositionally very similar compared to the early Paleozoic basement. The crustal composition from top to the bottom seems mainly felsic. Early Paleozoic mafic rocks are of minor volume and form mainly dikes. Their Sm-Nd model ages reveal two groups; one with ages of ca 1.8 Ga another with ages of £ 1.0 Ga. A meaningful interpretation of their geodynamic setting is not possible

Geología y Metalogenia de la Puna

Relationships between geological evolution, tectonic setting, magmatism and mineralization are pointed out. The geological Puna province is considered as two geological subprovinces: a northern and southern one. being the Olacapato megafault the boundary between them. Two principal pulses for the metalic mineralization are recognized: an Ordovician and a Miocenic one. Three north-southward mineralizated belts for the Ordovician time are described: eastern (Zn, Pb, Ag, baritine), central polymetalic (Cu, Fe, Zn, Pb, baritine and quartz) and western (Au, quartz) which would be the southern end of some Bolivian belts. On the other hand, four transversal (WNW-ESE) mineralizated belts for the Miocenic times, associated with the transversal volcanic ranges are described. From north to south: Coyahuaima (Sn, Ag, Pb, Sb); Quevar (Ag, Pb, Zn); Antofalla (Pb, Ag, Zn); Carachipampa (Cu). At last, relationships between the geological evolution of the Puna province and the non-metalic mineral occurrences are described, pointing out that northern Puna can be defined as "metal-bearing region" and the southern Puna as "nonmetal bearing regíon".En este trabajo se puntualizan una serie de conceptos sobre las relaciones existentes entre evolución geológica y metalogénesis de la Puna. El análisis de la sedimentación, magmatismo y metamorfismo de la provincia geológica Puna, permite diferenciarla en dos subprovincias con historia geológica y metalogenia propia que son: Puna Austral y Puna Septentrional. Ambas subprovincias están separadas por una megafractura regional de rumbo ONO-ESE, el lineamiento de Olacapato o Transpuneño. La región en estudio se considera como una pieza clave en el desarrollo del orógeno andino

Descripción geoquímica y geocronológica de secuencias volcánicas neógenas de Trasarco, en el extremo oriental de la Cadena Volcánica Transversal del Quevar (Noroeste de Argentina)

Se realizaron 34 nuevas dataciones K/Ar y 39 análisis geoquímicos de elementos mayoritarios, trazas y tierras raras, que implican nuevas aportaciones sobre las secuencias volcánicas neógenas de trasarco pertenecientes a la cadena volcánica transversal del Quevar. Esta cadena volcánica parte del arco volcánico actual con dirección W N W-ESE hasta las cercanías de la localidad de San Antonio de los Cobres. Se han reconocido y estudiado centros volcánicos ubicados en el extremo oriental de la misma. Los diferentes pulsos detectados en cada uno de estos centros (Aguas Calientes, Acay, El Morro-Orrganullo y Tocomar) son geoquímica y petrogr á ficamente homogéneos. Se interpreta que las cámaras magmáticas involucradas no han estado estratificadas composicionalmente ni han tenido sectores enriquecidos en cristales. Como excepción, el centro eruptivo Acay muestra un rango composicional desde términos andesíticos a riolíticos. En este caso, se interpreta un fraccionamiento de la cámara magmática en pulsos de edad similar. La composición isotópica del centro eruptivo Aguas Calientes indica una fuerte componente cortical en la formación de los magmas. Es posible explicar su origen a partir de fusión cortical. Las determinaciones geocronológicas realizadas muestran pulsos volcánicos a los 17-19 Ma, 13-12 Ma, 10 Ma, 7-6 Ma, 1-0.5 Ma en esta región de los Andes Centrales.New geochronological data (34) and 39 new geochemical analyses have been made in the Neogene backarc volcanic sequences in the “El Quevar Transversal Volcanic Chain” defined by Viramonte et al (1984a). This chain starts at the present N-S arc with WNW-ESE trend. New volcanic centres have been recognised and analysed at the eastern end of this chain. The different pulses from each volcanic centre (Aguas Calientes, Acay, El Morro - Organullo and Tocomar) are petrographically and geochemically homogeneous. This suggests that the magma chambers related in each volcano, were geochemically homogeneous and did not have crystal enriched sectors. The Acay eruptive centre is an exception of this assumption; a compositionally differentiated magmatic chamber could be inferred. The isotopic composition of the Aguas Calientes emission centre has a crust signature in its origin, related with melts generated by crustal fussion. The geochronological determinations show volcanic pulses at 17-19 Ma, 13-12 Ma, 10 Ma, 7-6 Ma, 1-0.5 Ma in this region of the Central Andes

Descripción geoquímica y geocronológica de secuencias volcánicas neógenas de Trasarco, en el extremo oriental de la Cadena Volcánica Transversal del Quevar (Noroeste de Argentina)

New geochronological data (34) and 39 new geochemical analyses have been made in the Neogene backarc volcanic sequences in the “El Quevar Transversal Volcanic Chain” defined by Viramonte et al (1984a). This chain starts at the present N-S arc with WNW-ESE trend. New volcanic centres have been recognised and analysed at the eastern end of this chain. The different pulses from each volcanic centre (Aguas Calientes, Acay, El Morro - Organullo and Tocomar) are petrographically and geochemically homogeneous. This suggests that the magma chambers related in each volcano, were geochemically homogeneous and did not have crystal enriched sectors. The Acay eruptive centre is an exception of this assumption; a compositionally differentiated magmatic chamber could be inferred. The isotopic composition of the Aguas Calientes emission centre has a crust signature in its origin, related with melts generated by crustal fussion. The geochronological determinations show volcanic pulses at 17-19 Ma, 13-12 Ma, 10 Ma, 7-6 Ma, 1-0.5 Ma in this region of the Central Andes

Forecasting volcanic ash dispersal and coeval resuspension during the April-May 2015 Calbuco eruption

Atmospheric dispersion of volcanic ash from explosive eruptions or from subsequent fallout deposit resuspension causes a range of impacts and disruptions on human activities and ecosystems. The April-May 2015 Calbuco eruption in Chile involved eruption and resuspension activities. We overview the chronology, effects, and products resulting from these events, in order to validate an operational forecast strategy for tephra dispersal. The modelling strategy builds on coupling the meteorological Weather Research and Forecasting (WRF/ARW) model with the FALL3D dispersal model for eruptive and resuspension processes. The eruption modelling considers two distinct particle granulometries, a preliminary first guess distribution used operationally when no field data was available yet, and a refined distribution based on field measurements. Volcanological inputs were inferred from eruption reports and results from an Argentina-Chilean ash sample data network, which performed in-situ sampling during the eruption. In order to validate the modelling strategy, results were compared with satellite retrievals and ground deposit measurements. Results indicate that the WRF-FALL3D modelling system can provide reasonable forecasts in both eruption and resuspension modes, particularly when the adjusted granulometry is considered. The study also highlights the importance of having dedicated datasets of active volcanoes furnishing first-guess model inputs during the early stages of an eruption.Fil: Reckziegel, Florencia Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Bustos, Emilce. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Leonardo, Mingari. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Folch Duran, Arnau. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Collini, E.. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Viramonte, Jose German. Universidad Nacional de Salta; ArgentinaFil: Romero, J.. Centro de Investigación y Difusión de Volcanes de Chile; Chile. Universidad de Atacama; ChileFil: Osores, María Soledad. Comision Nacional de Actividades Espaciales; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Descripción geoquímica y geocronológica de secuencias volcánicas neogenas de Trasarco, en el extremo oriental de la Cadena Volcánica Transversal del Quevar (Noroeste de Argentina)

Se realizaron 34 nuevas dataciones K/Ar y 39 análisis geoquímicos de elementos mayoritarios, trazas y tierras raras, que implican n u evas aportaciones sobre las secuencias volcánicas neógenas de trasarco pertenecientes a la cadena volcánica transversal del Queva r. Esta cadena volcánica parte del arco volcánico actual con dirección W N W-ESE hasta las cercanías de la localidad de San Antonio de los Cobres. Se han reconocido y estudiado centros volcánicos ubicados en el extremo oriental de la misma. Los diferentes pulsos detectados en cada uno de estos centros (Aguas Calientes, Acay, El Morro-Organullo y Tocomar) son geoquímica y petrogr á ficamente homogéneos. Se interpreta que las cámaras magmáticas involucradas no han estado estratificadas composicionalmente ni han tenido sectores enriquecidos en cristales. Como excepción, el centro eru p t ivo A c ay muestra un rango composicional desde términos andesíticos a riolíticos. En este caso, se interpreta un fraccionamiento de la cámara magmática en pulsos de edad similar. La composición isotópica del centro eruptivo Aguas Calientes indica una fuerte componente cortical en la formación de los magmas. Es posible explicar su origen a partir de fusión cortical. Las determinaciones geocronológicas realizadas muestran pulsos volcánicos a los 17-19 Ma, 13-12 Ma, 10 Ma, 7-6 Ma, 1-0.5 Ma en esta región de los Andes Centrales

Eruption dynamics of the 22–23 April 2015 calbuco volcano (Southern Chile): Analyses of tephra fall deposits

After 54 years since its last major eruption in 1961, Calbuco Volcano (Ensenada, Southern Chile) reawakened with few hours of warning on 22 April 2015 at 18:05 local time. The main explosive eruption consisted of two eruption pulses (lasting ~1.5 and 6 h each one) on 22 and 23 April, producing stratospheric (>15 km height) eruption columns. The erupted materials correspond to porphyritic basaltic andesite (~55 wt.% of SiO2). The tephra fall affected mainly the area northeast of the volcano and the finest ash was deposited over Southern Chile and Patagonia Argentina. We studied the tephra fall deposits of both pulses in terms of stratigraphy, distribution, volume, emplacement dynamics and eruption source parameters. Here, we show field observations that have been made 5-470 km downwind and distinguish five layers (Layers A, B, B1, C and D) representing different stages of the eruption evolution: eruption onset (Layer A; pulse 1), followed by the first paroxysmal event (Layer B; pulse 1), in some places interbedded by layer B1, tentatively representing the sedimentation of a secondary plume during the end of pulse 1. We recognized a second paroxysm (Layer C; pulse 2) followed by the waning of the eruption (Layer D; pulse 2). The total calculated bulk tephra fall deposit volume is 0.27 ± 0.007 km3 (0.11-0.13 km3 dense rock equivalent), 38% of which was erupted during the first phase and 62% during the second pulse. This eruption was a magnitude 4.45 event (VEI 4 eruption) of subPlinian type.Fil: Romero, J. E.. Universidad de Atacama; ChileFil: Morgavi, D.. Università di Perugia; ItaliaFil: Arzilli, F.. University of Manchester; Reino UnidoFil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Caselli, Alberto Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro; ArgentinaFil: Reckziegel, Florencia Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Díaz Alvarado, J.. Universidad de Atacama; ChileFil: Polacci, M.. University of Manchester; Reino UnidoFil: Burton, M.. University of Manchester; Reino UnidoFil: Perugini, D.. Università di Perugia; Itali

LLAMA Project

The project LLAMA, acronym of Long Latin American Millimetre Array is very briefly described in this paper. This project is a joint scientific and technological  undertaking of Argentina and Brazil on the basis of an equal investment share, whose mail goal is both to install and to operate an observing facility capable of exploring the Universe at millimetre and sub/millimetre wavelengths. This facility will be erected in the argentinean province of Salta, in a site located at 4830m above sea level.Instituto Argentino de RadioastronomíaFacultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica

Secondary lahar hazard assessment for Villa la Angostura, Argentina, using Two-Phase-Titan modelling code during 2011 Cordón Caulle eruption

This paper shows the results of secondary lahar modelling in Villa La Angostura town (Neuquén-Argentina) based on the Two-Phase-Titan modelling computer code, which aimed to provide decision makers a useful tool to assess lahar hazard during the 2011 Puyehue-Cordón Caulle Volcanic Complex eruption. Possible occurrence of secondary lahars that could reach the city was analized. The performance of the Two-Phase-Titan model using 15 m resolution DEMs developed from optical satellite images and from radar satellite images was evaluated. The output of these modellings showed inconsis- tencies that, based on field observations, were attributed to bad adjustment of DEMs to real topography. Further testing of results using more accurate radar based 10 m DEM, proved more realistic predictions. The procedure allowed to simulate the path of flows from Florencia, Las Piedritas and Colorado creeks, which are the most influenc- ing streams in Villa La Angostura. The output of the modelling is a valuable tool for city planning and risk management especially considering the glacial geomorphology features of the region, the strong urban development growth and the land occupation tendencies observed in last decade in Villa La Angostura and its surroundings

Preliminary conceptual model of the Cerro Blanco caldera-hosted geothermal system (Southern Puna, Argentina): Inferences from geochemical investigations.

The Cerro Blanco Caldera (CBC) is the youngest collapse caldera system in the Southern Central Andes (Southern Puna, Argentina). The CBC is subsiding with at an average velocity of 0.87 cm/year and hosts an active geothermal system. A geochemical characterization of emitted fluids was carried out based on the chemical and isotopic compositions of fumaroles, and thermal and cold springs discharged in this volcanic area with the aim of constructing the first hydrogeochemical conceptual model and preliminary estimate the geothermal potential. The main hydrothermal reservoir, likely hosted within the pre-caldera basement rocks, has a Na+-Clˉ(HCO3)ˉ composition with estimated temperatures ≥135 °C. The unconsolidated, fine-grained Cerro Blanco ignimbrite likely acts as the cap-rock of the hydrothermal system. The presence of phreatic eruption breccias in the surrounding area of the geothermal fumaroles supports the effectiveness of the pyroclastic deposit as sealing rocks. The isotopic data of water (δ18O and δD) indicate a meteoric recharge of the hydrothermal reservoir, suggesting as recharge areas the sectors surrounding the CBC, mainly towards the W and NW where large outcrops of the pre-caldera basement exist. A fault-controlled hydraulic connection between the hot springs and the hydrothermal reservoir is proposed for the Los Hornitos area. The fumaroles show the typical compositional features of hydrothermal fluids, being dominated by water vapor with significant concentrations of H2S, CH4 and H2. Considering the high geothermal gradient of this area (∼104 °C/km) and the relatively high fraction of mantle He (∼39%) calculated on the basis of the measured R/Ra values, the hydrothermal aquifer likely receives inputs of magmatic fluids from the degassing magma chamber. The preliminary geothermal potential at CBC was evaluated with the Volume Method, calculating up to E = 11.4*1018 J. Both the scarce presence of superficial thermal manifestations and the occurrence of an efficient cap-rock likely contribute to minimize the loss of thermal energy from the reservoir. The results here presented constitute the necessary base of knowledge for further accurate assessment of the geothermal potential and ultimately the implementation of the geothermal resource as a viable energy alternative for small localities or mining facilities isolated from the National Interconnected System due to their remote localization.Published1022136A. Geochimica per l'ambiente e geologia medicaJCR Journa