A recent pyroclastic density current (1963-64 AD? - 1976 AD?) from the Copahue volcano (I): Field geological evidences and radiocarbon age

Se describe un depósito atribuido a una corriente piroclástica sobre los flancos NE, E y SE del volcán Copahue. La datación radiocarbónica (F = 1.3678 ±0.0075) permite asignarle dos edades eruptivas posibles 1963-64 AD y 1976 AD (1961 AD?). Estimamos su importancia en la asignación de peligro volcánico del Copahue.We describe a historical pyroclastic deposit attributed to a pyroclastic density current (PDC) in the NE, E and SE flanks from the Copahue volcano. The radiocarbon dating (F = 1.3678 ±0.0075) enable to correlate this pyroclastic deposit with two possible eruption times 1963-64 AD and 1976 AD (1961 AD?). We consider its importance to assess the volcanic hazard of the Copahue volcano.Facultad de Ciencias Naturales y MuseoInstituto de Recursos MineralesCentro de Investigaciones Geológica

The December 22nd 2012 eruption of the Copahue volcano, Neuquén, Argentina: Characterization of the eruptive cycle and its products

Se describen las características y naturaleza de los productos emitidos durante la erupción del 22 de diciembre de 2012 del volcán Copahue. La erupción tuvo carácter pulsatorio, con máxima explosividad al inicio de la erupción (VEI 2) declinando rápidamente en aproximadamente 48 hs. La máxima altura de la columna eruptiva (1.500-2.000 m) fue registrada al inicio de la erupción y estuvo acompañada por una importante emisión de SO2. La pluma alcanzó 250 km en dirección ESE con anchos de 20 km (zonas proximales) y 35 km (zonas distales). Un segundo pulso eruptivo ocurrió por la tarde del 22 de diciembre, generando una pluma de menores dimensiones. Estos pulsos explosivos emitieron i) bloques y bombas balísticas y ii) piroclastos dispersados en suspensión, donde se destacan grandes fragmentos aplanados de escoria altamente vesiculada. El depósito de tefra se distribuyó en ambientes proximales alcanzando distancias de hasta unos 40 km desde el cráter activo y extendiéndose en un área de aproximadamente 200 km2. La tefra está constituida por componentes juveniles con diversos grados de vesiculación y componentes accesorios de composición subvolcánica alterados hidrotermalmente. Las bombas y bloques balísticos se dispersaron hasta 1.800-1.900 m alrededor de la boca eruptiva. Se estima un volumen total eruptado de aproximadamente 0,005 km3. La fase inicial de la erupción se asoció a una columna de magma en ascenso que al interactuar con el sistema hidrotermal superficial del volcán, gatilló una erupción hidromagmática. Una vez abierto el sistema, la descompresión condujo a la predominancia de una fragmentación magmática pulsatoria.This paper describes the characteristics, nature and distribution of the products of the 12/22/2012 eruption of the Copahue volcano (Neuquén Province, Argentina). The eruptive cycle was dominated by a pulsatory behavior, with a continuous decrease in the released energy since the onset of the eruption in the morning of December 22, when the eruptive column reached its maximum height (1,500-2,000 m). The volcanic plume extended for almost 250 km toward the ESE of the volcano and was characterized by a mean width of 20 km in proximal areas and 35 km in distal areas. This initial pulse was accompanied by significant SO2 emissions. A second, less intense, eruptive pulse occurred during the afternoon of December 22, leading to the development of a smaller volcanic plume. Eruption products can be classified as: i) ballistic bombs and blocks emitted from the eruptive center, and ii) fallout pyroclasts deposited directly from the volcanic plume, including large flattened juvenile fragments of highly vesiculated scoria. The characteristics of the eruptive event lead to the accumulation of tephra up to a distance of about 40 km from the crater, distributed along a surface of about 200 km2 to the SE of the volcano. Petrographic analysis performed on the fallout deposits showed the presence of juvenile fragments with different degrees of vesiculation and accessory fragments of hydrothermally altered subvolcanic rocks. Ballistic bombs and blocks were dispersed to a distance of 1,800-1,900 m from the eruptive center. We estimate a VEI 2 eruption intensity, with an emitted volume of about 0.005 km3 , which rapidly declined in about 48 hours after the onset of the eruption. The initial stages of the eruption were related to the interaction of an ascending column of magma with the shallow hydrothermal system of the volcano, triggering a hydromagmatic eruption. Once the conduit was open, the progressive decompression of the system led to an eruption dominated by a pulsatory magmatic fragmentation.Fil: Petrinovic, Ivan Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: D'elia, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigaciones Geológicas (i); ArgentinaFil: Guzman, Silvina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Bio y Geociencias del Noroeste Argentino; ArgentinaFil: Paez, Gerardo Nestor. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Recursos Minerales; ArgentinaFil: Outes, Ana Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Manzoni, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Delménico, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; ArgentinaFil: Balbis, Catalina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Carniel, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Hernando, Irene Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigaciones Geológicas (i); Argentin

A recent pyroclastic density current (1963-64 AD? - 1976 AD?) from the Copahue volcano (I): Field geological evidences and radiocarbon age

Se describe un depósito atribuido a una corriente piroclástica sobre los flancos NE, E y SE del volcán Copahue. La datación radiocarbónica (F = 1.3678 ±0.0075) permite asignarle dos edades eruptivas posibles 1963-64 AD y 1976 AD (1961 AD?). Estimamos su importancia en la asignación de peligro volcánico del Copahue.We describe a historical pyroclastic deposit attributed to a pyroclastic density current (PDC) in the NE, E and SE flanks from the Copahue volcano. The radiocarbon dating (F = 1.3678 ±0.0075) enable to correlate this pyroclastic deposit with two possible eruption times 1963-64 AD and 1976 AD (1961 AD?). We consider its importance to assess the volcanic hazard of the Copahue volcano.Facultad de Ciencias Naturales y MuseoInstituto de Recursos MineralesCentro de Investigaciones Geológica

Crystallization conditions and petrogenetic characterization of metaluminous to peraluminous calc-alkaline orogenic granitoids from mineralogical systematics: the case of the Cambrian magmatism from the Sierra de Guasayán (Argentina)

The Sierra de Guasayán (Eastern Sierras Pampeanas, Argentina) is formed by low to medium grade metamorphic rocks intruded by Cambrian metaluminous (La Soledad quartz-diorite), slightly peraluminous (Guasayán, El Escondido and El Martirizado granodiorite plutons), and strongly peraluminous (Alto Bello granodiorite) granitoids of the Pampean magmatic arc. Chemical compositions of amphibole, plagioclase, biotite, and titanite indicate that these granitoids were emplaced at low pressure (mostly <3 kbar) and temperature (<770 °C) under oxidizing conditions (QFM + 1 and QFM + 2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. Mineral assemblages and whole-rock and mineral chemistry of the granitoids from the Sierra de Guasayán indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, and titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, and sillimanite), and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, and magnetite). This hybrid nature is supported by the presence of abundant mafic microgranular enclaves and rapakivi texture and by published zircon Hf-isotope data (εHfi ranging from −4.76 to −0.12). This suggests, in turn, the involvement of hybridization in the genesis of these granitoids, which seems to be a common mechanism operating in the Pampean magmatic arc.Instituto de Recursos Minerale

The December 22nd 2012 eruption of the Copahue volcano, Neuquén, Argentina: Characterization of the eruptive cycle and its products

Se describen las características y naturaleza de los productos emitidos durante la erupción del 22 de diciembre de 2012 del volcán Copahue. La erupción tuvo carácter pulsatorio, con máxima explosividad al inicio de la erupción (VEI 2) declinando rápidamente en aproximadamente 48 hs. La máxima altura de la columna eruptiva (1.500-2.000 m) fue registrada al inicio de la erupción y estuvo acompañada por una importante emisión de SO2. La pluma alcanzó 250 km en dirección ESE con anchos de 20 km (zonas proximales) y 35 km (zonas distales). Un segundo pulso eruptivo ocurrió por la tarde del 22 de diciembre, generando una pluma de menores dimensiones. Estos pulsos explosivos emitieron i) bloques y bombas balísticas y ii) piroclastos dispersados en suspensión, donde se destacan grandes fragmentos aplanados de escoria altamente vesiculada. El depósito de tefra se distribuyó en ambientes proximales alcanzando distancias de hasta unos 40 km desde el cráter activo y extendiéndose en un área de aproximadamente 200 km2. La tefra está constituida por componentes juveniles con diversos grados de vesiculación y componentes accesorios de composición subvolcánica alterados hidrotermalmente. Las bombas y bloques balísticos se dispersaron hasta 1.800-1.900 m alrededor de la boca eruptiva. Se estima un volumen total eruptado de aproximadamente 0,005 km3. La fase inicial de la erupción se asoció a una columna de magma en ascenso que al interactuar con el sistema hidrotermal superficial del volcán, gatilló una erupción hidromagmática. Una vez abierto el sistema, la descompresión condujo a la predominancia de una fragmentación magmática pulsatoria.This paper describes the characteristics, nature and distribution of the products of the 12/22/2012 eruption of the Copahue volcano (Neuquén Province, Argentina). The eruptive cycle was dominated by a pulsatory behavior, with a continuous decrease in the released energy since the onset of the eruption in the morning of December 22, when the eruptive column reached its maximum height (1,500-2,000 m). The volcanic plume extended for almost 250 km toward the ESE of the volcano and was characterized by a mean width of 20 km in proximal areas and 35 km in distal areas. This initial pulse was accompanied by significant SO2 emissions. A second, less intense, eruptive pulse occurred during the afternoon of December 22, leading to the development of a smaller volcanic plume. Eruption products can be classified as: i) ballistic bombs and blocks emitted from the eruptive center, and ii) fallout pyroclasts deposited directly from the volcanic plume, including large flattened juvenile fragments of highly vesiculated scoria. The characteristics of the eruptive event lead to the accumulation of tephra up to a distance of about 40 km from the crater, distributed along a surface of about 200 km2 to the SE of the volcano. Petrographic analysis performed on the fallout deposits showed the presence of juvenile fragments with different degrees of vesiculation and accessory fragments of hydrothermally altered subvolcanic rocks. Ballistic bombs and blocks were dispersed to a distance of 1,800-1,900 m from the eruptive center. We estimate a VEI 2 eruption intensity, with an emitted volume of about 0.005 km3 , which rapidly declined in about 48 hours after the onset of the eruption. The initial stages of the eruption were related to the interaction of an ascending column of magma with the shallow hydrothermal system of the volcano, triggering a hydromagmatic eruption. Once the conduit was open, the progressive decompression of the system led to an eruption dominated by a pulsatory magmatic fragmentation.Centro de Investigaciones GeológicasInstituto de Recursos Minerale

Historic eruption of Tromen volcano: Geomorphologic and geochronological analysis on its northwestern area

Se estudiaron los productos más jóvenes del volcán Tromen en su sector NO. En base al análisis de reportes históricos en conjunto con datos geomorfológicos y una edad radiocarbono, se determinó que los últimos períodos de actividad del volcán Tromen son posteriores a 1400 d.C. Dos ciclos eruptivos constituidos por fenómenos de baja peligrosidad volcánica fueron registrados. El primero tuvo lugar entre los años 1400 y 1751 d.C. y el último entre 1820 y 1828 d.C. Los resultados obtenidos presentan relevancia para la evaluación del riesgo volcánico de las poblaciones cercanas.The youngest volcanic deposits of the NW flank of Tromen Volcano (Neuquén Province, Argentina) were addressed. Based on the analysis of historical reports, combined with geomorphologic and radiocarbon age determinations, the age of the volcanic activity was constrained to be younger than 1400 AD. Two volcanic cycles were recorded within this period, both constituted by low volcanic hazard products. The first one occurred between 1440 - 1751 AD, whereas the second one developed from 1820 to 1828 AD. The results of this work have relevance for the assessment of volcanic risk in the nearby townsCentro de Investigaciones GeológicasInstituto de Recursos MineralesFacultad de Ciencias Naturales y MuseoConsejo Nacional de Investigaciones Científicas y Técnica

Historic eruption of Tromen volcano: Geomorphologic and geochronological analysis on its northwestern area

Se estudiaron los productos más jóvenes del volcán Tromen en su sector NO. En base al análisis de reportes históricos en conjunto con datos geomorfológicos y una edad radiocarbono, se determinó que los últimos períodos de actividad del volcán Tromen son posteriores a 1400 d.C. Dos ciclos eruptivos constituidos por fenómenos de baja peligrosidad volcánica fueron registrados. El primero tuvo lugar entre los años 1400 y 1751 d.C. y el último entre 1820 y 1828 d.C. Los resultados obtenidos presentan relevancia para la evaluación del riesgo volcánico de las poblaciones cercanas.The youngest volcanic deposits of the NW flank of Tromen Volcano (Neuquén Province, Argentina) were addressed. Based on the analysis of historical reports, combined with geomorphologic and radiocarbon age determinations, the age of the volcanic activity was constrained to be younger than 1400 AD. Two volcanic cycles were recorded within this period, both constituted by low volcanic hazard products. The first one occurred between 1440 - 1751 AD, whereas the second one developed from 1820 to 1828 AD. The results of this work have relevance for the assessment of volcanic risk in the nearby townsCentro de Investigaciones GeológicasInstituto de Recursos MineralesFacultad de Ciencias Naturales y MuseoConsejo Nacional de Investigaciones Científicas y Técnica

Historic eruption of Tromen volcano: Geomorphologic and geochronological analysis on its northwestern area

Se estudiaron los productos más jóvenes del volcán Tromen en su sector NO. En base al análisis de reportes históricos en conjunto con datos geomorfológicos y una edad radiocarbono, se determinó que los últimos períodos de actividad del volcán Tromen son posteriores a 1400 d.C. Dos ciclos eruptivos constituidos por fenómenos de baja peligrosidad volcánica fueron registrados. El primero tuvo lugar entre los años 1400 y 1751 d.C. y el último entre 1820 y 1828 d.C. Los resultados obtenidos presentan relevancia para la evaluación del riesgo volcánico de las poblaciones cercanas.The youngest volcanic deposits of the NW flank of Tromen Volcano (Neuquén Province, Argentina) were addressed. Based on the analysis of historical reports, combined with geomorphologic and radiocarbon age determinations, the age of the volcanic activity was constrained to be younger than 1400 AD. Two volcanic cycles were recorded within this period, both constituted by low volcanic hazard products. The first one occurred between 1440 - 1751 AD, whereas the second one developed from 1820 to 1828 AD. The results of this work have relevance for the assessment of volcanic risk in the nearby townsCentro de Investigaciones GeológicasInstituto de Recursos MineralesFacultad de Ciencias Naturales y MuseoConsejo Nacional de Investigaciones Científicas y Técnica

A contribution to the hazards assessment at Copahue volcano (Argentina-Chile) by facies analysis of a recent pyroclastic density current deposit

We recognised and interpreted a recent pyroclastic density current (PDC) deposit at the Copahue volcano (Southern Andes), through a field survey and a sedimentological study. The relationships between the behaviour of the PDCs, the morphology of the Río Agrio valley and the eruptive dynamics were interpreted. We identified two lithofacies in the deposit that indicate variations in the eruptive dynamics: i) the opening of the conduit and the formation of a highly explosive eruption that formed a diluted PDC through the immediate collapse of the eruptive column; ii) a continued eruption which followed immediately and records the widening of the conduit, producing a dense PDC. The eruption occurred in 2000 CE, was phreatomagmatic (VEI ≤ 2), with a vesiculation level above 4000 m depth and fragmentation driven by the interaction of magma with an hydrothermal system at ca. 1500 m depth. As deduced from the comparison between the accessory lithics of this deposit and those of the 2012 CE eruption, the depth of onset of vesiculation and fragmentation level in this volcano is constant in depth. In order to reproduce the distribution pattern of this PDC's deposit and to simulate potential PDC's forming-processes, we made several computational modelling from “denser” to “more diluted” conditions. The latter fairly reproduces the distribution of the studied deposit and represents perhaps one of the most dangerous possible scenarios of the Copahue volcanic activity. PDCs occurrence has been considered in the last volcanic hazards map as a low probability process; evidences found in this contribution suggest instead to include them as more probable and thus very important for the hazards assessment of the Copahue volcano.Fil: Balbis, Catalina. 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: Petrinovic, Ivan Alejandro. 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: Guzmán, Silvia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentin

Kinematic partitioning in the Southern Andes (39° S–46° S) inferred from lineament analysis and reassessment of exhumation rates

The Southern Andes are often viewed as a classic example for kinematic partitioning of oblique plate convergence into components of continental margin-parallel strike-slip and transverse shortening. In this regard, the Liquiñe-Ofqui Fault Zone, one of Earth’s most prominent intra-arc deformation zones, is believed to be the most important crustal discontinuity in the Southern Andes taking up margin-parallel dextral strike-slip. Recent structural studies, however, are at odds with this simple concept of kinematic partitioning, due to the presence of margin-oblique and a number of other margin-parallel intra-arc deformation zones. However, knowledge on the extent of such zones in the Southern Andes is still limited. Here, we document traces of prominent structural discontinuities (lineaments) from the Southern Andes between 39° S and 46° S. In combination with compiled low-temperature thermochronology data and interpolation of respective exhumation rates, we revisit the issue of kinematic partitioning in the Southern Andes. Exhumation rates are maximal in the central parts of the orogen and discontinuity traces, trending predominantly N–S, WNW–ESE and NE–SW, are distributed across the entire width of the orogen. Notably, discontinuities coincide spatially with large gradients in Neogene exhumation rates and separate crustal domains characterized by uniform exhumation. Collectively, these relationships point to significant components of vertical displacement on these discontinuities, in addition to horizontal displacements known from published structural studies. Our results agree with previously documented Neogene shortening in the Southern Andes and indicate orogen-scale transpression with maximal vertical extrusion of rocks in the center of the transpression zone. The lineament and thermochronology data call into question the traditional view of kinematic partitioning in the Southern Andes, in which deformation is focused on the Liquiñe-Ofqui Fault Zone.Deutsche ForschungsgemeinschaftUniversität Hamburg (1037