Time lag between metamorphism and crystallization of anatectic granites (Córdoba, Argentina)

SHRIMP and LA-ICP-MS analyses carried out on zircons from the Río de los Sauces granite revealed their metamorphic and igneous nature. The metamorphic zircons yielded an age of 537±4.8 (2σ)Ma that probably predates the onset of the anatexis during the Pampean orogeny. By contrast, the igneous zircons yielded a younger age of 529±6 (2σ)Ma and reflected its crystallization age. These data point to a short time lag of ca. 8Myr between the High Temperature (HT) metamorphic peak and the subsequent crystallization age of the granite. Concordia age of 534±3.8 (2σ)Ma, for both types of zircon populations, can be considered as the mean age of the Pampean HT metamorphism in the Sierras de Córdoba

Granitos anatécticos de las Sierras Pampeanas de Córdoba (Argentina): edades U-Pb SHRIMP y estudio LAICP- MS de elementos traza en circón de metamorfismo y cristalización diacrónicos

In this contribution we present new U-Pb SHRIMP ages and in situ LA-ICP-MS trace element geochemistry of zircon crystals from the Río de los Sauces anatectic granite, Córdoba, Argentina. Notable difference in texture and composition allowed us to identify two zircon populations in a single granite sample that are interpreted as reflecting metamorphic and igneous origins. Zircons regarded as restitic crystals entrained during the melt segregation yielded a slightly older concordia age of 537.1 ± 4.8 Ma (2σ) than those interpreted as igneous, dated at 529 ± 6 (2σ) Ma. Inherited metamorphic zircons are interpreted to represent solid-state growth during high temperature metamorphism of the Pampean orogeny at the onset of the anatexis or metamorphic peak. By contrast, igneous zircons would record the crystallization age of Zr within the Río de los Sauces granite. The textural, compositional and geochronological data of both zircon populations suggest that the inception of the anatexis, the melt segregation and crystallization occurred during a short period of time of 8 myEn este trabajo se aportan nuevos datos de edades U-Pb SHRIMP y análisis in situ LA-ICP-MS de elementos traza de circones provenientes del granito Río de los Sauces, Córdoba, Argentina. A partir de marcadas diferencias texturales y composicionales se pudieron identificar dos poblaciones de circones en una misma muestra del granito, las cuales sugieren orígenes metamórficos e ígneos. Las edades concordia obtenidas en los circones metamórficos e ígneos fueron de 537,1 ± 4,8 Ma (2σ) y 529 ± 6 (2σ) Ma, respectivamente. Se interpreta que los circones metamórficos representan el crecimiento en estado sólido durante el metamorfismo de alta temperatura de la orogenia Pampeana, durante el inicio o el clímax de la anatexia. Por su parte, las edades de los circones ígneos representan la edad de cristalización del granito Río de los Sauces. Los datos texturales, composicionales y geocronológicos de ambas poblaciones de circones sugieren que el inicio de la anatexia, la segregación del fundido y la cristalización ocurrieron durante un periodo breve de tiempo de 8 ma

Granite emplacement by crustal boudinage: example of the Calmayo and El Hongo plutons (Córdoba, Argentina)

This study deals with the structure and emplacement of the Calmayo and El Hongo trondhjemite plutons (Famatinian belt of Córdoba, Argentina). It provides structural data from the granites and the country rocks and a study of the magnetic fabric in the plutons. New U/Pb geochronological data yield intrusion ages of 512.1 ± 3.4 Ma and 500.6 ± 4.5 Ma for the Calmayo and El Hongo plutons respectively. The El Hongo massif and the southern part of the Calmayo trondhjemite preserve magmatic structures, whereas the northern domain of Calmayo shows the imprint of solid-state deformation. The main foliation in the country rocks outlines a boudin-like pattern at the map scale and the granites are located along boudin necks, suggesting that the emplacement of these trondhjemite plutons was linked to large-scale boudinage of the country rocks.Fil: D'eramo, Fernando Javier. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tubía, José M.. Universidad del País Vasco; EspañaFil: Pinotti, Lucio Pedro. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vegas, Néstor. Universidad del País Vasco; EspañaFil: Coniglio, Jorge Enrique. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Demartis, Manuel. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aranguren, Aitor. Universidad del País Vasco; EspañaFil: Basei, Miguel. Universidade de Sao Paulo; Brasi

Milka Kronegold de Brodtkorb: challenges of a woman geologist in the 20th century

Milka Kronegold de Brodtkorb se graduó en 1957 como Licenciada en Ciencias Naturales (orientación Geología) en la Universidad de Buenos Aires y se doctoró en la misma universidad en 1963. Se especializó en mineralogía y metalogenia con formación de posgrado en Munich y Heidelberg, Alemania. Milka tuvo un activo desempeño profesional en la Comisión Nacional de Energía Atómica, Fabricaciones Militares y la entonces Dirección Nacional de Geología y Minería. Ingresó a la carrera del Investigador Científico del CONICET en 1973 donde fue designada Investigadora Superior en 1999. Dictó numerosos cursos de posgrado sobre mineralogía y paragénesis de menas en varias universidades argentinas y formó gran cantidad de discípulos, especialmente en mineralogía de menas. Sus cerca de 400 publicaciones versaron sobre mineralogía, paragénesis mineral y metalogenia, con obras de síntesis de las cuales fue coautora o editora, entre ellas se destacan los libros Especies Minerales de Argentina. En su larga trayectoria dirigió unos 40 becarios, tesistas, e investigadores. Su itinerario científico fue reconocido a través de varias distinciones, entre otras de la Asociación Geológica Argentina; recibió el premio Strobel de la Universidad de Buenos Aires, fue designada Académica de la Academia Nacional de Ciencias y Doctora Honoris Causa de la Universidad Nacional de Río Cuarto.Milka Kronegold de Brodtkorb graduated with a bachelor’s degree in Natural Sciences (majoring in Geology) in 1957 and received her doctoral degree in 1963, both from the Universidad de Buenos Aires. She specialized in mineralogy and metallogeny with postgraduate training in Munich and Heidelberg, Germany. Milka played an active professional role in the Comisión Nacional de Energía Atómica, Fabricaciones Militares and the then Dirección Nacional de Geología y Minería. She joined the CONICET as a scientific researcher in 1973 and attained the senior category in 1999. She taught numerous postgraduate courses on ore mineralogy and ore paragenesis at various Argentine universities, and trained a large number of students, mainly in ore microscopy. Her nearly 400 publications, dealing with mineralogy, mineral paragenesis and metallogeny, included books -either written or edited by her- synthesizing the state of those disciplines, among which Mineral Species of Argentina stands out. Throughout her long career she supervised the work of some 40 scholars, doctoral students and researchers. She was honoured for her scientific career with several awards and honorary memberships from, inter alia, the Asociación Geológica Argentina and the Universidad de Buenos Aires (Strobel Award). She was elected Academician of the Academia Nacional de Ciencias, Córdoba and given an Honoris Causa doctorate by the Universidad Nacional de Río Cuarto. Her scientific and professional itinerary was closely integrated with the formal and informal academic networks that allowed her to achieve her objectives and face new challenges.Fil: Ametrano, Silvia Juana. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Petrología y Mineralogia; ArgentinaFil: Montenegro, Teresita Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Pezzutti, Norma. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales. Dirección de Geología Regional; ArgentinaFil: Coniglio, Jorge Enrique. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentin

Magma chamber growth models in the upper crust: A review of the hydraulic and inertial constraints

Finite volumes of magma moving in confinement, store hydraulic potential energy for the generation, control and transmission of power. The Pascal´s principle in a hydraulic jack arrangement is used to model the vertical and lateral growth of sills. The small input piston of the hydraulic jack is equivalent to the feeder dike, the upper large expansible piston equivalent to the magmatic chamber and the inertial force of the magma in the dike is the input force. This arrangement is particularly relevant to the case of sills expanding with blunt tips, for which rapid fracture propagation is inhibited. Hydraulic models concur with experimental data that show that lateral expansion of magma into a sill is promoted when the vertical ascent of magma through a feeder dike reaches the bottom contact with an overlying, flat rigid-layer. At this point, the magma is forced to decelerate, triggering a pressure wave through the conduit caused by the continued ascent of magma further down (fluid-hammer effect). This pressure wave can provide overpressure enough to trigger the initial hydraulic lateral expansion of magma into an incipient sill, and still have enough input inertial force left to continue feeding the hydraulic system. The lateral expansion underneath the strong impeding layer, causes an area increase and thus, further hydraulic amplification of the input inertial force on the sides and roof of the incipient sill, triggering further expansion in a self-reinforcing process. Initially, the lateral pressure increase is larger than that in the roof allowing the sill to expand. However, expansion eventually increases the total integrated force on the roof allowing its uplift into either a laccolith, if the roof preserves continuity, or into a piston bounded by a circular set of fractures. Hydraulic models for shallow magmatic chambers, also suggest that laccolith-like intrusions require the existence of a self-supported chamber roof. In contrast, if the roof of magmatic chambers loses the self-supporting capacity, lopoliths and calderas should be expected for more or less dense magmas, respectively, owing to the growing influence of the density contrast between the host rock and the magma.Fil: Aragon, Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: D'eramo, Fernando Javier. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente.; ArgentinaFil: Pinotti, Lucio Pedro. Universidad Nacional de Río Cuarto; ArgentinaFil: Demartis, Manuel. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente.; ArgentinaFil: Tubía Martinez, José María. Universidad del Pais Vasco - Euskal Herriko Unibertsitatea, Campus Bizkaia;Fil: Weinberg, Roberto F.. Monash University; AustraliaFil: Coniglio, Jorge Enrique. Universidad Nacional de Río Cuarto; Argentin

Mapeo litológico y mineralógico del batolito devónico Cerro Áspero, usando imágenes ASTER, Sierras Pampeanas Orientales, Argentina

The present study evaluates ASTER image processing as a technique to assist the lithological and mineralogical mapping oflarge granitic bodies and associated hydrothermal alteration assemblages related to the Cerro Áspero batholith, in Sierra de Comechingones, Argentina. This batholith was formed by the successive emplacement of several sub circular, high-level crust plutons that intruded, in the Upper Devonian, to metamorphic sequences of high to medium grade reworked by shear zones. Each of these plutons developed internal, external and roof units, and dyke swarms. Internal units are composed by porphyritic biotite monzogranites and external, roof units and dyke swarms are dominated by two-mica and muscovite leucocratic monzogranites to quarz-rich alkali-feldspar granites. The main associated mineralizations are W-Mo magmatic-hydrothermaldeposits and postbatholith epithemal fluorite deposits of cretaceous age. Supervised classification, principal component analyses and emissivity calculations were made to identify lithological composition and variations within the different plutons that comprise the Cerro Áspero batholith. This methodology allowed us to have a better and precise mapping of the study area as well as the contacts between the different plutons that comprise the Cerro Áspero batholith. The classification with spectral angle mapper methods allowed to identify the different sectors with hydrothermal alteration (argillic and silicification). The argillic alteration is mainly associated with epithermal fluorite deposits74339440

Extreme F activities in late Pegmatitic events as a key factor for lile and HFSE enrichment: The Angel Pegmatite, Central Argentina

The Ángel pegmatite forms part of the Comechingones pegmatitic field, in central Argentina, which is made up of pegmatites characterized by low to intermediate degrees of fractionation, classified as beryl-columbite-phosphate subtype pegmatites. These pegmatites are syntectonic with a regional shear zone. The Ángel pegmatite contains associations with quartz, microcline, plagioclase, a first generation of muscovite (muscovite I), beryl, members of the columbite group, triplite, and montebrasite. This association is locally affected by two stages of replacement. The first replacement stage is characterized by early albitization, followed by the development of associations of cleavelandite, quartz, Fe-rich elbaite (elbaite I), a second generation of muscovite (muscovite II), topaz, lacroixite, fluorapatite, pollucite, columbite-(Mn), and Hf-rich zircon. Muscovite II replaces montebrasite and muscovite I, and is characterized by slight enrichments in F, Rb, and Cs. The second replacement stage generated a new mineral association characterized by muscovite III, Fe-poor elbaite (elbaite II), Cs-micas, and U-rich hydroxykenomicrolite. Muscovite III replaces muscovite II and is characterized by strong enrichments in F, Cs, and, to a lesser extent, Rb. In turn, muscovite III is replaced by the Cs-micas sokolovaite and nanpingite. The high F content of the nanpingite suggests that this could be the F- analogue of nanpingite, which would be a new mineral. The sequence of replacement is indicative of an increase in the F activity in the latest pegmatitic fluids. The high F activity of these fluids favored the transport of Ta, U, Bi, Hf, Rb, Cs, and Li, and the formation of F-rich micas could be the mechanism for precipitating these LILE and HFSE elements. The syntectonic emplacement of this pegmatite in a large shear zone could be a decisive factor in the migration of these late evolved fluids rich in F, LILE, and HFSE

Mapeo litológico y mineralógico del batolito devónico Cerro Áspero, usando imágenes ASTER, Sierras Pampeanas Orientales, Argentina

En este trabajo se presentan los resultados obtenidos utilizando técnicas de procesamiento de imágenes Aster para asistir al mapeo litológico y mineralógico de grandes cuerpos graníticos y de la alteración hidrotermal asociada al batolito Cerro Áspero, Sierra de Comechingones, Argentina. Este batolito fue construido por el emplazamiento sucesivo de varios plutones subcirculares, epizonales, que intruyeron en el Devónico Superior, a secuencias metamórficas de alto a mediano grado retrabajadas por fajas de deformación. Cada uno de estos plutones desarrolló unidades internas, externas, cuspidales y enjambres de diques. Las unidades internas están compuestas de monzogranitos porfídicos con biotita y las unidades externas, cuspidales y los enjambres de dique están dominados por leucogranitos cuyas composiciones varían desde monzogranítica hasta granitos alcali-feldespáticos, ricos en cuarzo. Las principales mineralizaciones asociadas son depósitos magmáticoshidrotermales de W-Mo y depósitos de fluorita epitermal, post-batolíticos, de edad cretácica. Para identificar la composición litológica y las variaciones en los plutones que lo componen se realizó clasificación supervisada, análisis de componentes principales y cálculos de emisividad. Esta metodología permitió un mejor y más detallado mapeo en el área de estudio, así como precisar los contactos entre los plutones que componen el batolito. La clasificación obtenida con el método SAM (spectral angle mapper) permitió la determinación de diferentes alteraciones hidrotermales (argílica y sílicificación). La alteración argílica está asociada principalmente con depósitos de fluorita epitermal.The present study evaluates ASTER image processing as a technique to assist the lithological and mineralogical mapping of large granitic bodies and associated hydrothermal alteration assemblages related to the Cerro Áspero batholith, in Sierra de Comechingones, Argentina. This batholith was formed by the successive emplacement of several sub circular, high-level crust plutons that intruded, in the Upper Devonian, to metamorphic sequences of high to medium grade reworked by shear zones. Each of these plutons developed internal, external and roof units, and dyke swarms. Internal units are composed by porphyritic biotite monzogranites and external, roof units and dyke swarms are dominated by two-mica and muscovite leucocratic monzogranites to quarz-rich alkali-feldspar granites. The main associated mineralizations are W-Mo magmatic-hydrothermal deposits and postbatholith epithemal fluorite deposits of cretaceous age. Supervised classification, principal component analyses and emissivity calculations were made to identify lithological composition and variations within the different plutons that comprise the Cerro Áspero batholith. This methodology allowed us to have a better and precise mapping of the study area as well as the contacts between the different plutons that comprise the Cerro Áspero batholith. The classification with spectral angle mapper methods allowed to identify the different sectors with hydrothermal alteration (argillic and silicification). The argillic alteration is mainly associated with epithermal fluorite deposits.Fil: Radice, Stefania. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Pinotti, Lucio Pedro. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Maffini, María Natalia. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Campanella, Osvaldo Hector. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; ArgentinaFil: Ducart, Diego F.. Universidade Estadual do Campinas. Instituto de Geociencias; BrasilFil: Coniglio, Jorge Enrique. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; ArgentinaFil: Demartis, Manuel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: D'eramo, Fernando Javier. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

The Farallon-Aluk ridge collision with South America: Implications for the geochemical changes of slab window magmas from fore- to back-arc

The collision of a divergent ocean ridge may evolve into two end cases: in the continuity of ocean-floor subduction, or in the detachment of the subducted plate. The northern Patagonia active plate margin has the unique situation that in Cenozoic time it has been subjected to two divergent ridge collisions, each one representing one of the end members. The Neogene Antarctica-Nazca divergent ridge collision evolved as a continuous ocean-floor subduction system, promoting a magmatic hiatus at the arc axis, the obduction of part of the ridge ocean-floor in the fore-arc, and basaltic volcanism in the back-arc. In contrast, the Paleogene Farallon-Aluk divergent ridge collision evolved into a transform margin, with the detachment and sinking of the Aluk plate and the development of a large slab window. As in the previous case, this collision promoted a magmatic hiatus at the arc axis, but the tectono-magmatic scenario changed to postorogenic synextensional volcanism that spread to the former fore-arc (basalt, andesite, rhyolite) and former back-arc (bimodal ignimbrite flare-up, basalt). Geochemistry of this slab window synextensional volcanism shows more MORB-like basalts towards the former fore-arc, and MORB-OIB-like basalts towards the former back-arc. Instead, an isolated undeformable crustal block in the former back-arc, with an "epeirogenic" response to the slab window and extensional regime, was covered by OIB-type basalts after uplift. Major elements show that slab window basalts reach TiO2 values up to 3 wt%, as compared with the top value of 1.5 wt% of arc magmas. Besides, the MgO with respect to (FeOt + Al2O3) ratio helps to distinguish slab window magma changes from the former fore-arc to the former back-arc and also with respect to the "epeirogenic" block. Higher contents of HFS elements such as Nb and Ta also help to distinguish this slab window from arc magmas and also, to distinguish slab window magma changes from the former fore-arc to the former back-arc and "epeirogenic" block settings. The isotope compositions of slab window magmatism show a disparate coeval array from MORB to crustal sources, interpreted as a consequence of the lack of protracted storage and homogenization due to the extensional setting.Facultad de Ciencias Naturales y Muse

Magmatic folds in the La Fronda trondhjemite pluton, Sierras Pampeanas at Córdoba, Argentina

From structural and magnetic fabric patterns, this work reports a complex folded structure in the La Fronda pluton, a small trondhjemite massif located in the Sierras de Córdoba which form the eastern part of the Sierras Pampeanas in Argentina. Isoclinal folds with no thickening at the hinge zones deform the compositional banding of these igneous rocks. Both the orientation of axial surfaces and fold axes vary from place to place and do not concur with the orientation of folds from the metamorphic country rocks. Microstructural data point to a fabric formed by grain-supported flow in a crystal-rich magma during the imprint of a vanishing regional stress fiel