Geología y petrología del basamento de la Sierra de San Luis al oeste de Tilisarao, región del Batolito de Renca

Fil: López de Luchi, Mónica Graciela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Syn-kinematic magma ascent and batholith inflation (Sierra de San Luis/Argentina)

The measurement of the anisotropy of the magnetic susceptibility (AMS) is now routinely used since more than four decades in the analyses of rock fabrics in granitic rocks (e.g. Stacy 1960, Henry 1975, Gleizes et al. 1993). Even though the intensity of fabrics in granitoids is often weakly developed the significance of orientation and shape of crystals is the same like in other deformed rock types. By revealing the distribution of fabrics in plutonic rocks one of the still ongoing discussions in granite tectonics may be addressed: How did those sometimes voluminous batholiths were inflated in the middle crust? We are presenting magnetic fabric data on a series of Devonian batholiths that intruded the polyphase deformed metaclastites of the Sierra de San Luis (32°100– 33°200 S / 65°150 – 66°200 W) in central Argentina. Regional considerations on the tectonic regime during the emplacement of the batholiths are inferred from combined field, microstructural and AMS observations...conferenc

Provenance and tectonic setting of the protoliths of the Metamorphic Complexes of Sierra de San Luis

A major and trace element based characterization of the metasedimentary protoliths of three metamorphic units of Sierra de San Luis (Pringles Metamorphic Complex, San Luis Formation and Conlara Metamorphic Complex) is presented. Geochemistry indicates a dominance of shales in the protoliths of San Luis Formation, whereas greywackes and shales made up the Conlara Metamorphic complex and mainly greywackes, the Pringles Metamorphic Complex. Both major element data and trace element ratios (i.e. Th/Sc, Th/U,) indicate a source with an average upper crustal composition for the protoliths of the Pringles Metamorphic Complex, the San Luis Formation and the shales of the Conlara Metamorphic complex. A component with less evolved signature may be inferred for the metagreywackes of the Conlara metamorphic Complex. Mixed sourced detritus are indicated for the three units with clastic material resulting mainly from both andesitic and acidic/recycled detritus. The overall data consistently suggest a continental island arc and/or active margin setting as the more probable geodynamic scenario for the deposition of the sedimentary precursors of the studied units. In this context, a back-arc setting can account for the mixed nature of the inferred source areas with uplifted old basement and arc-related detritus as the end members of the mixtures. The inferred back-arc basin would have evolved through the Cambrian receiving the sediments derived from the Pampean Orogen to the east combined with probably some old crust exposures and to the west the source might have been controlled by the active continental margin. © 2003 Asociación Geológica Argentina.Fil:Cerredo, M.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Did Patagonia collide with Gondwana in the Late Paleozoic? Some insights from a multidisciplinary study of magmatic units of the North Patagonian Massif

The origin of Patagonia and its relations with the South American crustal blocks to the north have been a matter of debate for decades. We report results from a multidisciplinary study centered on Paleozoic granitoids exposed in the northeastern corner of the North Patagonian Massif. Microstructural and magnetofabric studies reveal two suites of granitoids. Late Carboniferous (?) granitoids (Yaminué Complex, Tardugno Granodiorite, Cabeza de Vaca leucogranite) were emplaced and subsequently deformed in a major NNE-SSW compressive stress regime that also provoked top-to-the-SW thrust deformation in shallow crustal levels. Gravity and geobarometric studies show that the same major deformation event has been recorded at different crustal levels. The age and type of deformation of this event recorded across the northern boundary of Patagonia strongly supports a Late Carboniferous – Early Permian frontal collision between Patagonia and Gondwana. This major deformation event ceased by 281 Ma when the Navarrete Plutonic Complex, which shows mainly magmatic fabrics, was emplaced under a far-field WNW-ESE stress regime. Crustal continuity between the North Patagonian Massif and the Pampia and Arequipa- Antofalla terranes is suggested by similar Late Paleoproterozoic crustal model ages, comparable detrital zircon ages in Early Paleozoic successions, the apparent continuity of an Early Ordovician continental magmatic arc and paleomagnetic data. Reconciliation of this evidence with the Late Paleozoic frontal collision is obtained in a tectonic model that suggests that the North Patagonian Massif is a parautochthonous crustal block

Geochronology of quarz-monzodioritic to tonalitic Stock Musters, an Ordovician intrusive from Valcheta, Northpatagonian Massif

Esta contribución informa la primera edad de cristalización U-Pb en circón de un stock monzodiorítico cuarzoso a tonalítico, aquí denominado formalmente como Diorita Musters, y perteneciente al conjunto de granitoides asociados al plutón leucogranitíco Valchetaque forma parte del conjunto de granitoides de edad ordovícica temprana aflorantes en el sector nororiental del Macizo Norpatagónico(Complejo plutónico Punta Sierra, Busteros et al. 1998). Los resultados de los análisis U-Pb en circones revelan una edad de cristalización ordovícica inferior (470 ± 2 Ma; MSWD =0.99) para este pulso magmático, confirmando la extensión de este magmatismoordovícico por más de 200 km2 y afirmando su importancia regional y conexión con la orogenia Famatiniana.This contribution reports the first U-Pb age in zircons of a quartz-monzodioritic to tonalitic stock, here formally denominated as Musters Diorite and belonging to the group of Early Ordovician granitoids outcropping in the northeastern sector of the Northern Patagonian Massif (Punta Sierra Plutonic Complex, Busteros et al. 1998). Our results of U-Pb analyses in zircons reveal an Early Ordovician crystallization age (470 ± 2 Ma; MSWD =0.99; N=70/89) for this magmatic pulse, confirming the extension of this magmatism for more than 200 km2 and showing its regional importance and connection with the Famatinian OrogenyFil: Grillo Vidal, Carolina Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Ciencias Geológicas. Area de Petrologia; ArgentinaFil: Martínez Dopico, Carmen Irene. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Ciencias Geológicas. Area de Petrologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: López de Luchi, Mónica G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentin

The Conlara metamorphic complex: Lithology, provenance, metamorphic constraints on the metabasic rocks, and chime monazite dating

The Conlara Metamorphic Complex, the easternmost complex of the Sierra de San Luis, is a key unit to understand the relationship between the late Proterozoic-Early Cambrian Pampean and the Upper Cambrian-Middle Ordovician Famatinian orogenies of the Eastern Sierras Pampeanas. The Conlara Metamorphic Complex extends to the east to the foothills of the Sierra de Comechingones and to the west up the Río Guzmán shear zone. The main rock types of the CMC are metaclastic and metaigneous rocks that are intruded by Ordovician and Devonian granitoids. The metaclastic units comprise fine to medium-grained metagreywackes and scarce metapelites with lesser amounts of tourmaline schists and tourmalinites whereas the metaigneous rocks encompass basic and granitoids rocks. The former occur as rare amphibolite interlayered within the metasedimentary rocks. The granitic component corresponds to a series of orthogneisses and migmatites (stromatite and diatexite). The CMC is divided in four groups based on the dominant lithological associations: San Martin and La Cocha correspond mainly to schists and some gneisses and Santa Rosa and San Felipe encompass mainly paragneisses, migmatites and orthogneisses. The Conlara Metamoprphic Complex underwent a polyphase metamorphic evolution. The penetrative D2-S2 foliation was affected by upright, generally isoclinal, N-NE trending D3 folds that control the NNE outcrop patterns of the different groups. An earlier, relic S1 is preserved in microlithons. Discontinuous high-T shear zones within the schists and migmatites are related with D4 whereas some fine-grained discontinuous shear bands attest for a D5 deformation phase. Geochemistry of both non-migmatitic metaclastic units and amphibolites suggest that the Conlara Metamorphic Complex represents an arc related basin. Maximun depositional ages indicate a pre- 570 Ma deposition of the sediments. An ample interval between sedimentation and granite emplacement in the already metamorphic complex is indicated by the 497 ± 8 Ma age of El Peñon granite. D1-D2 history took place at 564 ± 21 Ma as indicated by one PbSL age calculated for the M2 garnet of La Cocha Group. D3 is constrained by the pervasively solid-state deformed Early Ordovician granitoids which exhibits folded xenoliths of the D1-D2 deformed metaclastic rocks. Pressure-temperature pseudosections were calculated for one amphibolite using the geologically realistic system MnNCKFMASHTO (MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3). Peak metamophic conditions (M2) indicate 6 kbar and 620 °C. Late chlorite on the rims and in cracks of garnet, along with titanite rims on ilmenite and matrix plagioclase breaking down to albite suggests that the P-T path moved back down. Monazite analyses yield isochron Th–U–Pb ages ranging from 446 to 418 Ma. The oldest age of 446 ± 5 Ma correspond to a migmatite from the Santa Rosa Group. Monazites in samples from the La Cocha and the San Martin group crystallized at decreasing temperatures, followed by the 418 ± 10 Ma low-Y2O3 monazites in one sample of the la Cocha Group that was also obtained from a migmatite, and would likely mark a later stage of a retrograde metamorphism New CHIME monazite ages presented here likely represent post-peak fluid assisted recrystallization that are similar to amphibole and muscovite cooling ages. Therefore the monazite ages may represent a re-equilibration of the monazite on the cooling path of the basement complex.Fil: López de Luchi, Mónica G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Martínez Dopico, Carmen Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Cutts, Kathryn Ann. Universidade do Estado de Rio do Janeiro; BrasilFil: Schulz, Bernhard. Institute of Mineralogy; AlemaniaFil: Siegesmund, Siegfried. Universität Göttingen; AlemaniaFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Montenegro, Teresita Francisca. 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; Argentin

Geochronology of quarz-monzodioritic to tonalitic Stock Musters, an Ordovician intrusive from Valcheta, Northpatagonian Massif

Esta contribución informa la primera edad de cristalización U-Pb en circón de un stock monzodiorítico cuarzoso a tonalítico, aquí denominado formalmente como Diorita Musters, y perteneciente al conjunto de granitoides asociados al plutón leucogranitíco Valchetaque forma parte del conjunto de granitoides de edad ordovícica temprana aflorantes en el sector nororiental del Macizo Norpatagónico(Complejo plutónico Punta Sierra, Busteros et al. 1998). Los resultados de los análisis U-Pb en circones revelan una edad de cristalización ordovícica inferior (470 ± 2 Ma; MSWD =0.99) para este pulso magmático, confirmando la extensión de este magmatismoordovícico por más de 200 km2 y afirmando su importancia regional y conexión con la orogenia Famatiniana.This contribution reports the first U-Pb age in zircons of a quartz-monzodioritic to tonalitic stock, here formally denominated as Musters Diorite and belonging to the group of Early Ordovician granitoids outcropping in the northeastern sector of the Northern Patagonian Massif (Punta Sierra Plutonic Complex, Busteros et al. 1998). Our results of U-Pb analyses in zircons reveal an Early Ordovician crystallization age (470 ± 2 Ma; MSWD =0.99; N=70/89) for this magmatic pulse, confirming the extension of this magmatism for more than 200 km2 and showing its regional importance and connection with the Famatinian OrogenyFil: Grillo Vidal, Carolina Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Ciencias Geológicas. Area de Petrologia; ArgentinaFil: Martínez Dopico, Carmen Irene. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Ciencias Geológicas. Area de Petrologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: López de Luchi, Mónica G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentin

El distrito polimetálico Gonzalito, Río Negro

El distrito Gonzalito, previamente conocido como distrito Laguna Grande (Angelelli, 1984), comprende dos fajas mineralizadas con Pb, Ag, Zn, V, [Au], localizadas en el Complejo Igneo Metamórfico Gonzalito. La Faja Oriental incluye las minas Gonzalito, Vicentito, La Querencia y Polito, y la Faja Occidental las minas Tres Marías y María Teresa. Los trabajos mineros previos reconocieron la disposición escalonada de vetas de sulfuros polimetálicos en estas minas. Trabajos recientes establecen que estas vetas están asociadas espacial y temporalmente con esquistos negros metalíferos, e identifican a estos yacimientos como tipo estratoligado, y más específicamente, como SEDEX sujeto a varios eventos metamórficos precámbricos de grado mediano a alto, y posteriormente afectados por removilización hidrotermal durante el Paleozoico superior y Jurásico. El ciclo Precámbrico dió como resultado dos tipos de depósitos: removilizados vetiformes polimetálicos y diseminados estratoligados (esquisto negro), ambos con altos contenidos en Pb, Zn, Ag y V.Centro de Investigaciones Geológica

El distrito polimetálico Gonzalito, Río Negro

El distrito Gonzalito, previamente conocido como distrito Laguna Grande (Angelelli, 1984), comprende dos fajas mineralizadas con Pb, Ag, Zn, V, [Au], localizadas en el Complejo Igneo Metamórfico Gonzalito. La Faja Oriental incluye las minas Gonzalito, Vicentito, La Querencia y Polito, y la Faja Occidental las minas Tres Marías y María Teresa. Los trabajos mineros previos reconocieron la disposición escalonada de vetas de sulfuros polimetálicos en estas minas. Trabajos recientes establecen que estas vetas están asociadas espacial y temporalmente con esquistos negros metalíferos, e identifican a estos yacimientos como tipo estratoligado, y más específicamente, como SEDEX sujeto a varios eventos metamórficos precámbricos de grado mediano a alto, y posteriormente afectados por removilización hidrotermal durante el Paleozoico superior y Jurásico. El ciclo Precámbrico dió como resultado dos tipos de depósitos: removilizados vetiformes polimetálicos y diseminados estratoligados (esquisto negro), ambos con altos contenidos en Pb, Zn, Ag y V.Centro de Investigaciones Geológica

Did Patagonia collide with Gondwana in the Late Paleozoic? Some insights from a multidisciplinary study of magmatic units of the North Patagonian Massif

The origin of Patagonia and its relations with the South American crustal blocks to the north have been a matter of debate for decades. We report results from a multidisciplinary study centered on Paleozoic granitoids exposed in the northeastern corner of the North Patagonian Massif. Microstructural and magnetofabric studies reveal two suites of granitoids. Late Carboniferous (?) granitoids (Yaminué Complex, Tardugno Granodiorite, Cabeza de Vaca leucogranite) were emplaced and subsequently deformed in a major NNE-SSW compressive stress regime that also provoked top-to-the-SW thrust deformation in shallow crustal levels. Gravity and geobarometric studies show that the same major deformation event has been recorded at different crustal levels. The age and type of deformation of this event recorded across the northern boundary of Patagonia strongly supports a Late Carboniferous - Early Permian frontal collision between Patagonia and Gondwana. This major deformation event ceased by 281 Ma when the Navarrete Plutonic Complex, which shows mainly magmatic fabrics, was emplaced under a far-field WNW-ESE stress regime. Crustal continuity between the North Patagonian Massif and the Pampia and Arequipa- Antofalla terranes is suggested by similar Late Paleoproterozoic crustal model ages, comparable detrital zircon ages in Early Paleozoic successions, the apparent continuity of an Early Ordovician continental magmatic arc and paleomagnetic data. Reconciliation of this evidence with the Late Paleozoic frontal collision is obtained in a tectonic model that suggests that the North Patagonian Massif is a parautochthonous crustal block