Jorge Coniglio’s research while affiliated with National University of Río Cuarto and other places

Two consecutive orogenies, named Pampean and Famatinian, delineated most of the metamorphic and igneous rocks that are currently exposed in the Sierras Pampeanas. During the Cambrian and early Ordovician periods development of a classic magmatic arc and another magmatic/migmatitic belt took place, the latter nowadays located in the easternmost sector of the Eastern Sierras Pampeanas. The Sierra Norte-Ambargasta batholith is considered the Pampean magmatic arc and shows a calc-alkaline trend, similar to those defined by magmas associated with andesitic sources. The continuation to the north of this Cambrian magmatism is represented by smaller plutons located in the Cumbres Calchaquíes, Guasayán and Cordillera Oriental ranges, emplaced in areas of medium-upper crust, mostly in schists, phyllites and slates of low- and medium metamorphic grade. The assimilation of metasedimentary material from the host rocks by magmas similar to those described in the Sierra Norte-Ambargasta would have been the process that gave rise to the geochemical characteristics of these granitoids. On the contrary, the southernmost Sierras de Córdoba exposes a deep crustal section dominated by migmatites and high-grade metamorphic rocks with a diverse variety of protoliths such as pelites-greywackes and amphibolites, and minor marbles, calc-silicate and ultramafic rocks. In this context, the diversity of magmatic rocks is due to the variety of protoliths involved in the region of origin, which gave rise to granitic and trondhjemitic melts related to leucocratic bodies formed during partial melting. On the other hand, the early Ordovician back-arc magmatism exposed in the Eastern Sierras Pampeanas is more homogeneous in the northern part compared to the southern one. It is represented by Pl-rich tonalites and granodiorites with high Na2O, CaO, Al2O3 and Sr contents, which define calcic to calc-alkaline, slight to highly peraluminous and magnesian to ferroan series. The petrogenesis of these rocks would be related to a combination of plagioclase fractionation from tonalitic-trondhjemitic primary melts and hybridization processes between two end-members (monzogranitic and tonalitic-trondhjemitic melts), which gave rise to an intermediate magmatism of hybrid composition. The source area for this Famatinian magmatism could have its origin within the same domain where the Cambrian hot orogen developed along the Pampean convergent margin. Small amounts of Grt-bearing leucogranites and pegmatitic dykes could have been generated in response to the emplacement of intermediate magmas in middle-crust levels producing the partial melting of metasediments from Puncoviscana Fm. The Famatinian back-arc was associated with a generalized extension, marine sediment deposition and anatexis in the lower crust, causing differentiation and crustal recycling in the high-grade Pampean metamorphic basement.

RESUMEN La porción norte del bloque de piso de la faja de cizalla Guacha Corral en la Sierra de Comechingones se encuentra dominada por una secuencia migmática clasificada como metatexitas metasedimentarias y metatexitas máficas, cuyos contactos generalmente son transicionales y se caracterizan por presentar distintas morfologías en función del contenido de fundido presente. Los resultados obtenidos del análisis estructural de las

Mineralogy of the reaction zones in the contact between tonalitic intrusives and ultramafic rocks, neoproterozoic-lower paleozoic basement (Alta Gracia, Córdoba). This paper presents new mineralogical data of reaction zones developed in the contact between bodies of tonalitic composition and serpentinized ultramafic rocks, located in the eastern slope of the Sierra Chica, Córdoba. The reaction zones are greenish, brownish to light greyish coloured rocks and 0.1 to 1 meters thick. Three mineralogical zones are distinguished from tonalitic dykes (metatonalites)

Polymetallic quartz veins (Pb-Zn-Cu-Ag±Au) are a common feature in the Sierras Pampeanas de Córdoba, Argentina. In the «Las Guindas» district the veins are structurally controlled by kilometric-scale NNW-trending brittle transtensional shear zones that crosscut migmatitic and mylonitic regional foliations. Mineralization occurs near Devonian granitic rocks. Within the transtensional shear zones, the veins have two dominant strikes: 1) 330°, which coincides with the main direction of sinistral strike-slip, and 2) 300° corresponds to tensional fractures (Fig. 1c). Quartz samples from veins with different kinematic indicators were studied with the aim to determine the role of deformation on mineral deposition and fluids entrapment.

Polymetallic quartz veins (Pb-Zn-Cu-Ag±Au) outcrop in the southern Sierras Pampeanas de Córdoba, Argentina...

En este trabajo se caracterizaron 10.000 toneladas de escombreras de mármoles a fin de definir sus parámetros físico-mecánicos y mineralógicos y determinar su aptitud como componente principal en capas granulares de una estructura de pavimento. Aunque los coeficientes Los Ángeles (41-53%) exceden lo permitido en la especificación de referencia, la granulometría, plasticidad y California Bearing Ratio (C.B.R.) (76, 83, 100% al 97, 98 y 100% de la densidad máxima, respectivamente) satisfacen lo especificado, con condicionamientos. Por consiguiente, con un simple cribado, este material de escombrera podría ser utilizado en terraplenes, sub-bases y bases granulares de carreteras, constituyendo una alternativa: a) Ambientalmente sostenible: porque evita nuevas explotaciones y elimina un potencial pasivo ambiental; b) Técnicamente viable: ya que la capacidad portante de las capas granulares no se vería afectada; c) Económicamente conveniente: porque aporta un valor agregado a un sub-producto hoy desechado y reduce costos de explotación y transporte.

El basamento gnéisico-migmático del sector centro-norte de la Sierra Chica y parte oriental de la Sierra Grande de Córdoba, se encuentra asociado a una gran cantidad de intrusiones ígneas, las cuales hasta el momento poseían escasos antecedentes de investigación. En este trabajo, se identificaron cinco litologías ígneas que se agruparon en dos asociaciones en base a su morfología, reología y relaciones de campo. La primera, comprende intrusiones de morfología irregular, que incluyen monzogranitos, tonalitas y pegmatitas (denominadas de tipo I). Estos cuerpos poseen bordes lobulados y contactos transicionales con su roca encajante y su origen posiblemente se vincula con los procesos de anatexis cortical ocurridos durante el ciclo orogénico Pampeano. La segunda asociación, comprende intrusiones laminares (diques), que incluyen tonalitas-trondhjemitas y pegmatitas (llamadas de tipo II). Se caracterizan por presentar bordes rectos y contactos netos con su roca de caja y se encuentran asociados espacialmente con fajas de cizalla discretas estabilizadas en facies de anfibolita. A su vez, estas rocas intruyen de manera discordante a las intrusiones irre-gulares y al basamento gnéisico-migmático, por lo que su emplazamiento ha sido posterior. A partir de sus relaciones de yacencia, emplazamiento sin-cinemático con fajas de cizalla (estabilizadas en facies de anfibolita) y las edades 40 Ar/ 39 Ar obtenidas en este trabajo (450.92 ± 1.41 Ma y 434.53 ± 3.16 Ma), la generación y el emplazamiento de los cuerpos laminares habría ocurrido durante el ciclo orogénico Famatiniano. ABSTRACT Geology and geocronology of predevonic laminar and irregular intrusions in the central portion of Sierras de Córdoba. A large amount of igneous intrusions hosted by a gneissic-migmatic metamorphic basement crop out in the central-north part of the Sierra Chica and eastern boundary of the Sierra Grande de Córdoba. In this contribution, five igneous lithologies were identified and grouped into two distinctive rock groups according to their morphologies, rheology and field relationships. The first group includes irregular shaped monzogranites, tonalites and pegmatites (called type-I), having lobate and diffuse contacts with their surrounding host rocks. Field relationships suggest that these intrusions originated from crustal anatexis processes of different protoliths, correlated with similar processes occurred during the Pampean Orogeny. The second group includes laminar-shaped (dykes) tonalite-trondhjemites and pegmatites (called type-II), having straight and sharp contacts with their host rocks. They are spatially associated with narrow and localized shear zones stabilized in amphibolite facies. These igneous rocks invariably crosscut the irregular-shaped intrusives of the first group as well as gneissic and migmatic metamorphic host rocks of the basement, clearly reflecting a younger age of emplacement.

In the Comechingones pegmatitic field, central Argentina, leucogranite and pegmatite bodies crop out in a relatively narrow (25 × 10 km) belt, and were emplaced synkinematically with the main deformational event of the crustal-scale Guacha Corral shear zone during the Early Ordovician (~ 475 Ma). These leucogranites and pegmatites are geochemically evolved rocks with high silica and alkalis, low Fe2O3, MgO, TiO2 and CaO, and high ASI values. The leucogranites display quite variable Sr and Nd isotope compositions (initial 87Sr/86Sr ratios from 0.7048 to 0.7170, and εNd values from + 2.0 to − 3.1), some of which do not overlap with almost any other pre-Famatinian rock from the Sierras de Córdoba. The major and trace element geochemistry and the particular Sr and Nd isotope compositions of the leucogranites are here explained by the following processes: (1) water-fluxed partial melting of amphibolites at relatively low P–T conditions generating currently unexposed granodioritic melts with unradiogenic 87Sr/86Sr ratios and radiogenic εNd values; (2) fractionation of mostly plagioclase and monazite leading to compositions close to the leucogranite melts; and (3) assimilation of metasedimentary rocks with crustal isotopic signatures, modelled by assimilation and fractional crystallization processes. The major, trace and isotope compositions of the pegmatites suggest a derivation from partial melting of the same metasedimentary protoliths of the Sierras de Córdoba that were assimilated by leucogranite melts. We propose a feedback relationship among deformation, anatexis, magma evolution and mass transfer in the context of such a crustal-scale shear zone in the foreland of the Famatinian orogen.

This study provides new insights about mechanisms of synkinematic interplay between dyking emplacement and ductile narrow shear zones formation in the Sierra Chica de Córdoba. A detailed analysis of structural, microstructural, geometric-scaling and geochronologic data is performed in order to demonstrate the important role that minor and meso-scale felsic dykes played in the formation of paired shear zones symmetrically from dyke contacts. This magmatism and associated deformation conspicuously overprint medium-to high grade metamorphic and igneous rocks of Pampean age. Internally, the shear zones are formed by mylonites with mineral paragenesis in the amphibolite facies and foliation planes totally concordant to dyke contacts. Low rheological contrast between igneous intrusions and host rocks, together with fast rates of magma channeling and emplacement, were responsible for a brittle mechanical regime at moderate to high temperatures (500–700 °C). Melt-filled shear fractures rapidly propagated while the host rock was being mylonitized at ductile conditions. Shear structures controlling dyke construction and mylonite formation adjust to a strike-slip dominated dextral transtensional regime. The predicted axes of finite maximum shortening (Z) and maximum extension (X) have NNE and NNW directions, respectively. Ar/Ar muscovite cooling ages determined for pegmatite dykes, yielded minimum crystallization ages between 451 ± 1 and 435 ± 3 My. These geochronological data are further supported by field structural relationships and the regional knowledge, pointing to a Famatinian age for magmatism and related narrow shear zones. This paper constitutes a new contribution reporting the occurrence of magmatism and strike-slip-dominated dextral transtension deformation in the inner foreland of the Famatinian accretionary orogen, developed in the Early Paleozoic along the southwestern Gondwana margin.

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. Pampean Orogeny. Pampean Metamorphism. Río de los Sauces granite. U-Pb SHRIMP dating. LA-ICP-MS analyses. KEYWORDS A B S T R A C T