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

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

Zircon U-Pb geochronology of the Chimpa volcano (Central Andes, Puna plateau, NW Argentina): Inferences on the temporal evolution of the magmatic system

We investigated the temporal evolution of the andesitic Chimpa volcano of the northern Puna plateau, Central Andes, situated at the geological boundary between the plateau and the Eastern Cordillera domains. The volcanic activity consisted in three constructive volcanic cycles (Basal, Cajon and Chimpa units) showing complex eruptive behaviors (ignimbrites, lava domes. block-and-ash flows, lava flows). We present new U-Pb analyses conducted on the zircon crystals from the Chimpa volcanic rocks. These analyses provide constraints on the magmatic/volcanic tempos and offer insights into the Th and U (and Th/U ratios) systematics of the analyzed zircon crystals. The results suggest a lifespan for volcanism ranging 7.5 to <7.0 Ma, in concomitance with the regional steady-state magmatic phase separating the first two pulses of ignimbritic flare-up in the Altiplano-Puna Volcanic Complex. Moreover, the analyzed zircon crystals exhibit Th/U ratios (0.11–0.34) and Th (33–8860 ppm) and U (52–4258 ppm) that indicate magmatic crystallization from poorly evolved melts at high temperatures. Some discrepancies exist between the calculated zircon concordia age for the third volcanic phase (Chimpa Unit, ca. 7.35 ± 0.071 Ma) and that of the second cycle (Cajon Unit, 6.98 ± 0.057 Ma). We interpret these differences as stemming from the presence of zircon antecrysts in the final eruptive melts. Indeed, a true pre-eruptive event of zircon crystallization (i.e., formation of autocrysts) could not be proven by the existing dataset.There is a geochronological affinity with some nearby volcanic rocks from the Puna plateau and the Eastern Cordillera domains, particularly considering the rhyolitic products of the Ramadas Volcanic Center and the andesitic to dacitic Almagro volcanic rocks. This highlights the complex behavior of the local magma plumbing system beneath this particular area, resulting in the emission of geochemically variegate volcanic rocks at similar times. This scenario suggests that the composition of the erupting melts are affected by the rheological behavior of the mid-upper-crustal MASH reservoir (the Altiplano-Puna Magmatic Body), which may either facilitate or impede the ascent of poorly evolved magmas derived from the deep crust towards the surface. From this point of view, the relative location of the volcanic centers relatively to the position of the geophysical anomaly may exert an important influence on the petrogenetic paths of magmas

Geochemistry and Geochronology descriptionsiguie of the Backarc Neo gene volcanic sequences in the eastern border of the Quevar Transversal Volcanic Range (NW Argentina)

[ES] 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 WNW-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 petrográficamente 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.[EN] New geochronological data (34) and 39 new geochemical analyses have been made in the Neogene backarc volcanic sequences in the “El Quevar Tr a n s versal Volcanic Chain” defined by Viramonte et al (1984a). This chain starts at the present N-S arc with WNWESE 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, A c ay, 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.Este trabajo ha sido financiado con aportes del proyecto CEE CI1-CT92-0098, del Consejo de Investigación de Universidad Nacional de Salta (proyecto 815/2) y del CONICET. Las sugerencias de dos revisores anónimos han sido de gran utilidad para la confección final del trabajo.Peer reviewe

Comparing the biotite and amphibole single-mineral thermobarometric models: A case study from the Cordillera de San Buenaventura volcanic rocks, Puna plateau of Central Andes (Argentina)

We applied a new thermobarometric model based solely on biotite composition to the trachyandesitic to rhyolitic volcanic rocks of the Cordillera de San Buenaventura, a long-lived magma plumbing system (spanning from the Late Miocene to the Holocene) in the Southern Puna plateau (Central Volcanic Zone of the Andean Cordillera). Within these rocks, biotite is a widespread mineral phase found in association with amphibole, as either glomerocrysts, mutual inclusions, or free phenocrysts. This allowed us to compare the biotite-only model with other thermobarometric estimates that rely on amphibole, mineral-melt, and mineral-mineral composition. Our goal was to determine the conditions of formation for biotite and its petrogenetic significance in the evolution of the Cordillera de San Buenaventura magma system. The results indicate that biotite crystallization occurred mainly at middle-to upper-crustal depths (2.1–5.1 kbar) with temperatures below 1000 °C (763–919 °C). The biotite-only T-P estimates for individual lithologies are consistent with those obtained using the amphibole-only model, and this is particularly true for the thermometer. Furthermore, our findings align with the existing petrogenetic models, which suggest extensive fractional crystallization, and with the analyses of mineral textures, that indicates events of magma replenishment. Therefore, our results support the validity of the biotite-only model and its ability to elucidate magmatic processes, including magma differentiation via fractional crystallization, magma ascent and cooling, and magma replenishment and/or mixing events

The Calama-Olacapato-El Toro fault system in the Puna Plateau, Central Andes: Geodynamic implications and stratovolcanoes emplacement

""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."

Descripción geoquímica y geocronológica de secuencias volcánicas neógenas de Trasarco en el extremo oriental de la Cadena Volcánica Transversal de Queevar (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 WNW-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 petrográficamente 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

Early Paleozoic long-lived silicic volcanism in the Eastern Puna Magmatic Belt, Argentina

In several locations along the Eastern Puna Magmatic Belt (EPMB) porphyritic rhyolite facies are interbedded with thinly bedded mudstone and fine-grained sandstone deposited during deepening of the marine setting. Previous research mainly focused on the northern part of EPMB, identified four main syn-sedimentary rhyolitic-dacitic volcanic episodes from Early to Late Ordovician, the oldest being Tremadocian (earliest Ordovician). In this contribution, we describe coherent rhyolite facies associated with volcaniclastic breccias in the central part of the EPMB (Cajón, Tuzgle, Concordia and Agua de Castilla creeks), and we present new geochemical data and U/Pb zircon ages on coherent rhyolite facies (Cajón, Huancar and Opla). The studied rhyolites are syn-sedimentary sills with peperitic margins. The coherent rhyolites have SiO2 content of ∼65–71 wt%, peraluminous signature, enrichment in LILE (Cs, Rb, Ba) and marked negative Sr, Ti and P anomalies. The REE patterns normalized to chondrite show a higher content of the light REE and a negative Eu anomaly (Eu/Eu* between 0.44 and 0.52). The integration of the regional data with our results suggests that at least two rhyolitic-dacitic volcanic episodes occurred during the Ordovician evolution of the EPMB: The Early Ordovician (∼485-462 Ma) including Tremadocian and Arenigian facies (Rio Taique, Niño Muerto, Huancar, Opla, northern Pastos Chicos, Agua Cavada, Muñayoc, oldest Quichagua, Cordón de Escaya, Cajón, Tuzgle, Concordia and Agua de Castilla); and the youngest Late Ordovician facies (∼449-443 Ma; Oplita, southern Pastos Chicos, Cordón de Escaya and youngest Quichagua). Hence, sedimentation and silicic volcanism across the Eastern Puna Magmatic Belt spanned at least in two episodes along the Ordovician period with more volume and duration during the Early Ordovician (ca. 20 Ma).Fil: Quiroga, Mirta Fátima. 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; ArgentinaFil: Ortiz Yañez, Agustín. 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; ArgentinaFil: Salado Paz, Natalia. 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; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto Geonorte; ArgentinaFil: Becchio, Raul Alberto. 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; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto Geonorte; ArgentinaFil: Alfaro, B.. 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; ArgentinaFil: Arnosio, M.. 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; ArgentinaFil: Bordese, Sofia. Geomap S.a.; ArgentinaFil: Raveggi, M.. Monash University; Australi

Estilo eruptivo y dinámica de flujo de las corrientes de densidad piroclásticas asociadas a la gran erupción del Cerro Blanco (4200 AP), Puna Austral

Durante la evolución del Complejo Volcánico Cerro Blanco (Puna Austral) ocurrió una de las erupciones holo - cenas más grandes de los Andes Centrales, la cual dió lugar a la caldera del Cerro Blanco y generó la ignimbrita ho- mónima (ICB). El objetivo de este trabajo es aportar nueva información respecto de la dinámica de este evento eruptivo a partir del análisis de facies y reconstrucción de la arquitectura interna de los depósitos ignimbríticos. Los resultados obtenidos permitieron inferir que la ICB es el resultado del emplazamiento de numerosas corrientes de densidad piroclásticas (CDPs) de tipo dominadas por >inercia> asociadas a colapsos periódicos de una columna eruptiva de tipo pliniana, la cual fue sostenida a lo largo de la mayor parte de la erupción, incluso durante la fase de colapso caldérico.Peer Reviewe

Eruptive style and flow dynamics of the pyroclastic density currents related to the Holocene Cerro Blanco eruption (Southern Puna plateau, Argentina)

The Pleistocene-Holocene Cerro Blanco Volcanic Complex (CBVC), one of the youngest caldera complexes in the Southern Central Andes, is the source of possibly one of largest Holocene eruptions on Earth, the 4.2 ka, Cerro Blanco eruption. This caldera forming eruption is the younger of two major explosive events from the CBVC. Previous work has estimated the range from VEI 6 to 7, yet to date there is no detailed study of the stratigraphy and volcanology of the proximal deposits and dynamics of the Cerro Blanco eruption. Here we present the first detailed analysis of the eruptive products of the Holocene Cerro Blanco eruption that reveal the eruptive sequence highlighting the flow dynamics of the related pyroclastic density currents (PDCs). The PDCs were mainly inertia-dominated, however, channelization of parental PDCs into deep valleys resulted in the flow transformation to forced convection-dominated flows. In addition, topographic constriction in valleys enhanced the sedimentation rate producing regressive bed forms and ultimately the avulsion of the main path of the PDCs resulting in flooding of secondary valleys. A model is presented whereby simultaneous convective and collapsing eruptive column dynamics were established and sustained throughout the eruption. Towards its end, instabilities of the column occurred in response to the climax of a protracted incremental caldera collapse. This eruptive sequence is similar to those observed in well-documented small collapse calderas. An important unresolved issue for the CB eruption is it volume. The currently estimated volume of 83 km3 (DRE) by Fernando-Turiel et al. (2019) is inconsistent with the size of the Cerro Blanco caldera and to date the over thickening of the distal ash by local rework is poor assessed. Further work is needed to fully evaluate this mismatch and accurately estimate the volume of this important Holocene eruption