Depositional style and tectonostratigraphic evolution of El Bierzo Tertiary sub-basin (Pyrenean orogen, NW Spain)

El Bierzo Tertiary sub-basin (Oligocene-Miocene, NW Spain) is a small remnant of the western Duero Basin, a nonmarine broken foreland basin developed in front of the Cantabrian Mountains (Pyrenean orogen). The alluvial infill of El Bierzo Tertiary sub-basin consists of a coarsening-upward succession from fluvial (Toral Formation) to alluvial-fan deposits (Las Médulas Formation) and reflects the uplift of the Cantabrian Mountains, in the north, and then of the related Galaico-Leoneses Mountains, in the south. These alluvial deposits show signs of having been laid down mainly by catastrophic flows (flood-dominated systems) and consist of three main depositional elements, namely, flood-plain fines, and lobe and channel conglomerates and sandstones. The vertical stacking patterns of these deposits and their relationships to the Alpine structures permit to unravel the tectonosedimentary evolution of the basin. The alluvial-plain element is the main constituent of a wide unconfined alluvial plain (Toral Formation) during the early stages of basin evolution, whereas the channel and lobe elements form a set of relatively small, laterally confined alluvial fans (Las Médulas Formation) fed first from the north and then from the south. Las Médulas deposits form two superposed units, the lower unit, cut by the Alpine thrusts, shows a progradational character, and the upper unit, which postdates most of the thrusts but not the youngest ones, displays a composite retrogradational trend. This organisation reflects the interplay between thrust emplacement and alluvial-fan sedimentation and suggests that maximum progradation took place during the climax of Alpine deformation

In memoriam of Andrés Pérez-Estaún

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Depositional style and tectonostratigraphic evolution of El Bierzo Tertiary sub-basin (Pyrenean orogen, NW Spain)

El Bierzo Tertiary sub-basin (Oligocene-Miocene, NW Spain) is a small remnant of the western Duero Basin, a nonmarine broken foreland basin developed in front of the Cantabrian Mountains (Pyrenean orogen). The alluvial infill of El Bierzo Tertiary sub-basin consists of a coarsening-upward succession from fluvial (Toral Formation) to alluvial-fan deposits (Las Médulas Formation) and reflects the uplift of the Cantabrian Mountains, in the north, and then of the related Galaico-Leoneses Mountains, in the south. These alluvial deposits show signs of having been laid down mainly by catastrophic flows (flood-dominated systems) and consist of three main depositional elements, namely, flood-plain fines, and lobe and channel conglomerates and sandstones. The vertical stacking patterns of these deposits and their relationships to the Alpine structures permit to unravel the tectonosedimentary evolution of the basin. The alluvial-plain element is the main constituent of a wide unconfined alluvial plain (Toral Formation) during the early stages of basin evolution, whereas the channel and lobe elements form a set of relatively small, laterally confined alluvial fans (Las Médulas Formation) fed first from the north and then from the south. Las Médulas deposits form two superposed units, the lower unit, cut by the Alpine thrusts, shows a progradational character, and the upper unit, which postdates most of the thrusts but not the youngest ones, displays a composite retrogradational trend. This organisation reflects the interplay between thrust emplacement and alluvial-fan sedimentation and suggests that maximum progradation took place during the climax of Alpine deformation

Structure of the Southern Patagonian Andes at 49ºS, Argentina

This paper describes Late Paleozoic Gondwanan and Late Cretaceous to Early Cenozoic Andean structures in the Southern Patagonian Andes and an associated Extra-Andean region between lakes San Martín and Viedma. The study area encompasses a 200-km-long W-E section between the Patagonian icefield and the 72ºW longitude meridian, in Argentine Patagonia. The oldest structures are of Late Paleozoic age and developed through at least two deformation phases during the Gondwanan Orogeny. The first deformation phase (Dg1) includes isoclinal and N-overturned WNW trending folds and associated thrusts, including duplexes. The second deformation phase includes NNE trending open folds (Dg2). Deformation occurred in non-metamorphic to very low-grade metamorphic conditions. A spaced rough cleavage is found near the first phase fold hinges. The Eocene and Miocene Andean structural compression resulted in a N-S oriented fold and thrust belt. This belt is comprised of three morphostructural zones from W to E, with distinctive topographic altitudes and structural styles: Andean; Sub-Andean; and Extra-Andean zones. The first corresponds to the inner fold and thrust belt, while the last two are part of the outer fold and thrust belt. The Andean zone (3400-2000m above sea level) is characterized by N-S to NNE trending, E-vergent, Cenozoic reverse faults and associated minor thrusts. The northern part of the Sub- Andean zone (2000-1500m above sea level) consists of W-vergent reverse faults and some NNE open folds. The southern part of the Andean zone includes tight folds with box and kink geometries, related to thrusts at deeper levels. In the Extra-Andean zone, with maximum heights of 1500m, the deformation is less intense, and gentle folds deform the Upper Cretaceous sediments. An inherited Jurassic N-S extensional fault system imposed a strong control on this morphostructural zonation. Also the variation of the Austral Basin sedimentary thickness in the N-S direction seems to have influenced the structural styles of the outer fold and thrust belt. Those differences in sedimentary thickness may be related to S-dipping transfer zones associated to W-E Jurassic extension. In turn, the transfer zones may have been controlled by the N-vergent WNW, Dg1, Gondwanan structural fabric

Polyorogenic structure of the San Rafael Block, Mendoza, Argentina: New data for the interpretation of the Chanic Orogen

The Paleozoic pre-Carboniferous rocks of the San Rafael Block, located to the east of the Los Reyunos Gondwanan Thrust, show Chanic structures (Late Devonian–early Carboniferous) with east vergence, which were generated in the absence of metamorphism. This Paleozoic succession is unconformably located on the basement of Cuyania. The rocks, located to the west of the Los Reyunos Thrust, were deformed by two fold episodes, the first and main (D1) west verging, developed under low to very low-grade metamorphic conditions, and the second (D2) east verging and mainly developed near Los Reyunos Reservoir. Therefore, the Los Reyunos Thrust must be considered a reactivation of a Chanic structure during the Gondwanan Orogeny (late Carboniferous–early Permian). The ancient Chanic thrust could be responsible for the overlay of the hinterland of the western branch of the Chanic Orogen on the foreland of its eastern branch, at the end of the collision between the Cuyania and Chilenia subplates. The results of this work have been related to those of nearby areas located to the north and west, which has allowed the elaboration of a model that explains the characteristics of the Chanic Orogen in this area. During the Carboniferous, the Los Reyunos Thrust was reactivated as a normal fault, facilitating the sedimentation of carboniferous rocks thousands of meters thick in its hanging wall and later, during the Gondwanan deformation, it underwent a tectonic inversion. During the Andean cycle, the Permian–Triassic beds of the Choiyoi Group were deposited in relation to NW–SE trending normal faults, giving rise to rollover structures. Finally, during the Cenozoic, Andean compression gave rise to the formation of an open antiform, in whose core is the Mesoproterozoic–Paleozoic basement of the San Rafael Block.Facultad de Ciencias Naturales y Muse

Evaluación Metalogenética y Estudio geológico-Estructural del Distrito Polimetálico San Antonio de Los Cobres. Provincia de Salta, República Argentina

El presente es un proyecto realizado en el marco del Convenio de cooperación y asistencia técnica en materia de Geología y Minería entre el Servicio Geológico Minero Argentino (SEGEMAR) y el Instituto Geológico y Minero de España (IGME)El proyecto se divide en dos partes. Parte I: Contexto geológico-estructural regional del complejo volcánico el Quevar. Parte II: Características estructurales y edad de las mineralizaciones y alteraciones asociadas en la quebrada de Incahuasi del complejo volcánico el Quevar.Fil: Seggiaro, R. Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales; Argentina.En el marco del Convenio de cooperación y asistencia técnica en materia de geología y minería entre el Servicio Geológico Minero Argentino (SEGEMAR) y el Instituto Geológico y Minero de España (IGME), el presente Proyecto ha consistido en realizar un estudio geológico integral del área comprendida entre el Complejo Volcánico El Quevar (CVEQ), El Oculto y la Caldera de Aguas Calientes, en el distrito San Antonio de los Cobres (provincia de Salta), con el fin de determinar los posibles factores que controlan la formación tanto de edificios volcánicos como de cuerpos mineralizados asociados. El sector estudiado está localizado a aproximadamente 30 km al oeste de San Antonio de los Cobres, dentro de La Puna Salteña. Las mineralizaciones desarrolladas en este distrito incluyen depósitos de Pb-Ag, Sb y Mn, y de Au, que se localizan en el interior del CVEQ y dentro de la caldera Aguas Calientes ubicada al este donde se encuentra la mina La Poma. El Proyecto se centró en el estudio detallado de las mineralizaciones localizadas en el sector occidental del CVEQ. El acceso a esta zona se realiza por la RN51 hasta aproximadamente 55 km al oeste-suroeste de San Antonio de los Cobres y a 17 km de la estación ferroviaria de Pocitos, desde donde parte un camino por la Quebrada Incahuasi hasta el campamento central de la Compañía Minera Picazas. Durante los trabajos de campo se realizaron observaciones, tomas de datos y mapeo expeditivo en el CVEQ y también en sus alrededores, analizándose el contexto tectónico y estratigráfico en el cual se emplazó el sistema volcánico integrado por los volcanes El Quevar, Mamaturi y Azufre. Los resultados del Proyecto fueron separados en dos partes; - Parte I aborda el contexto tectónico regional basado en información estratigrafía y estructural en el sector comprendido entre Olacapato - San Antonio de los Cobres y Pocitos – Santa Rosa de los Pastos Grandes. Con este objetivo se analizó la información estructural existente, se colectaron datos estructurales a lo largo de la traza del lienamiento Calama-Olacapato-El Toro (COT) y se realizó un análisis cinemático experimental mediante un modelado analógico, a escala, de la región estudiada. - Parte II presenta los estudios de detalle realizados en la zona de la Quebrada de Incahuasi en el sector centro sur-oeste del CVEQ, que vinculan las características estructurales, la edad de las mineralizaciones y de las alteraciones asociadas y las edades de emplazamiento de los cuerpos volcánicos vinculados a la mineralización. En este sector se realizó la toma de muestras de rocas alteradas y con mineralizaciones y de rocas frescas, el levantamiento de datos estructurales y la diferenciación de unidades volcánicas y descripciones in situ de tipos de alteración y mineralización. En gabinete se realizó la confección de mapas geológicos en el que se emplaza el área mineralizada, la descripción de unidades litoestratigrafícas, el procesamiento de datos estructurales regionales y locales y la descripción, el análisis microscópico de alteraciones y mineralizaciones y las dataciones de rocas frescas y alteradas. La dirección técnica del proyecto la han realizado Raúl E. Seggiaro (SEGEMAR) y Nemesio Heredia Carballo (IGME). Los análisis geocronológicos Ar/Ar fueron realizados por Janet Gabites (University of British Columbia, Vancouver, Canadá)

Evolución del basamento paleozoico de los Andes Norpatagónicos en el área de San Martín de los Andes (Neuquén, Argentina): petrología, edad y correlaciones

In San Martín de los Andes area (Argentinian Patagonia) the Palaeozoic basement consists of metamorphic and plutonic rocks. The metamorphic rocks include strongly deformed schists, gneisses and migmatites. Their geochemical and petrographic characteristics suggest that the protholith could have been a sequence of pelites and greywackes. Detrital zircon analysis (U-Pb Q-ICP-LA-MS) yielded a maximum depositional age of 501±14 Ma (Series 3 Cambrian) for this sedimentary protolith. Metasedimentary rocks are affected by a regional foliation defined by the minerals of the metamorphic peak. This is a S2 foliation, since relics of a former foliation are present in some samples. This regional foliation is locally affected by open folds that develop an incipient crenulation cleavage (S3). The high-grade metamorphism includes partial melting processes, where the incipient segregates intrude parallel to the regional foliation and also cut it in presence of abundant melt. Zircons from anatectic granites formed during this partial melting process yielded a U-Pb Concordia age of 434.1±4.5 Ma (Llandovery-Wenlock, Silurian). The age of maximum sedimentation and the anatectic age constrain the metamorphic evolution of the basement into the lower Palaeozoic (between upper Cambrian and lower Silurian). The igneous rocks of the basement are granodiorites, tonalities, and some gabbros that cut the metamorphic basement and contain xenoliths and roof pendants from the country rocks. These plutonic rocks are affected by low-grade metamorphism, with the development of discrete, centimetric to hectometric, brittle-ductile shear zones. The age of these igneous rocks has been constrained through U-Pb zircons analysis, carried out by several authors between ca. 370 and 400 Ma (Devonian). The maximum sedimentation age for the protolith and its metamorphic evolution seems to be related to an early Palaeozoic orogenic event, probably the Patagonian Famatinian orogeny. In contrast, the Devonian igneous rocks of San Martín de los Andes could represent a Devonian magmatic arc, related to subduction processes developed at the beginning of the Gondwanan orogenic cycle, which culminates with the Gondwanan orogeny.En el entorno de San Martín de los Andes (Patagonia argentina), el basamento Paleozoico está constituido por rocas metamórficas e ígneas. Las rocas metamórficas de esta área incluyen esquistos, gneises y migmatitas intensamente deformadas. Según sus características geoquímicas y petrográficas, el protolito de las mismas es considerado una alternancia de pelitas y grauvacas. Análisis de circones detríticos (U-Pb Q-ICP-LA-MS) permiten definir una edad máxima de sedimentación de 501±14 Ma (Series 3, Cámbrico) para este protolito sedimentario. Las rocas metasedimentarias se encuentran afectadas por una foliación regional definida por la asociación principal del pico metamórfico. Esta es una foliación de tipo S2, ya que se encuentran relictos de una foliación anterior en algunas muestras. Esta foliación regional, está localmente afectada por pliegues abiertos donde se desarrolla un clivaje de crenulación incipiente (S3). El metamorfismo de alto grado incluye un evento de fusión parcial, donde los primeros segregados se introducen a favor de la foliación S2 y la cortan en presencia de abundante fundido. Circones obtenidos de un granito anatéctico producido durante este evento de fusión parcial arrojaron una edad Concordia U-Pb de 434.1±4.5 Ma (Llandovery-Wenlock, Silúrico). La edad máxima de sedimentación y la edad de anatexis permiten acotar la evolución de las rocas metamórficas del basamento al Paleozoico inferior (entre el Cámbrico tardío y el Silúrico temprano). Las rocas ígneas del basamento son granodioritas y tonalitas, con menor proporción de gabros, las cuales cortan las rocas metamórficas y contienen xenolitos y roof pendants de las mismas. Por otra parte, estas rocas plutónicas fueron afectadas por un metamorfismo de bajo grado que llevan asociadas zonas de cizalla frágil-dúctil centimétricas a hectométricas. Edades U-Pb SHRIMP en circones restringe la edad de estas rocas entre 370 y 400 Ma (Devónico). La edad máxima de sedimentación de los protolitos de las rocas metamórficas y su evolución metamórfica podría estar relacionada a un evento orogénico del Paleozoico temprano, probablemente a la orogenia Famatiniana Patagónica. En contraste, las rocas plutónicas de San Martín de los Andes representarían un arco magmático, relacionado a una subducción que se habría producido al comienzo del ciclo orogénico Gondwánico, el cual culmina con la orogenia Gondwánica.Centro de Investigaciones Geológica

La estructura de la Serie Oriental en la zona del río Maule, Constitución (Chile)

Congreso Geológico Chileno "Geociencias hacia la comunidad" (15th, 2018, Concepción, Chile