General Roca, Argentina
General Roca, Argentina

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Gallego O.F.,CONICET | Cabaleri N.G.,CONICET | Armella C.,CONICET | Volkheimer W.,CONICET | And 3 more authors.
Journal of South American Earth Sciences | Year: 2011

A new Late Jurassic assemblage of " conchostracans", ostracods, bivalves and caddisfly cases from the locality " Estancia La Sin Rumbo", Chubut Province (Patagonia, Argentina) is recorded. The fossils occur in the upper part of an outcropping 45 m thick volcaniclastic lacustrine sequence of yellowish tuffs and tuffites of the Puesto Almada Member, which is the upper member of the Cañadón Asfalto Formation with U/Pb age of 161 ± 3. Ma. The sequence represents one sedimentary cycle composed of a (lower) hemicycle of expansion and a (higher) hemicycle of contraction of the water body. The invertebrates lived in small freshwater bodies during the periods of expansion of the lake. The occurrence of a great number of small spinicaudatans, associated with mud-cracks, is evidence of dry climatic conditions and suggests several local mortality events. The spinicaudatan record of the fushunograptid-orthestheriid (component of the Eosestheriopsis dianzhongensis fauna) and the presence of Congestheriella rauhuti Gallego and Shen, suggest a Late Jurassic (Oxfordian to Tithonian) age. Caddisfly cases are recorded for the first time in the Cañadón Asfalto Basin. © 2010 Elsevier Ltd.

Giambiagi L.,CONICET | Mescua J.,CONICET | Bechis F.,National University of Rio Negro | Martinez A.,National University of San Luis | Folguera A.,Institute Geologia y Recursos Minerales
Geosphere | Year: 2011

This paper presents a detailed investigation of the structure and evolution of the Precordillera southern sector (Argentina). We document the development and successive reactivation of regional and discrete structural grain through time, and discuss the existence of a large-scale mechanical anisotropy present in the lithosphere. Our kinematic studies indicate that the Permian orogeny generated a doubly vergent foldand-thrust belt of transpressive deformation, where strain was partitioned into two different types of deformation domains. The westvergent western domain was characterized by partitioned transpression with shortening dominating, and a strike-slip-dominated subdomain. The east-vergent eastern domain was characterized by pure contractional deformation. Our model for the Late Permian to Early Triassic evolution of the Pre cordillera involves a north-northwest-trending weakness zone affected by north-northeast- directed extension, generating an area with transtensional deformation during the Choiyoi volcanism development. Later, during the Triassic generation of the Cuyana rift basin, the northeast stretching direction was orthogonal to the rift trend, indicating pure extensional deformation. We propose a model where the clear parallelism between the distribution of an inferred early Paleozoic suture zone, a northnorthwest- trending late Paleozoic belt, and Permian-Triassic rift-related magmatism indicates the reactivation of a northnorthwest- trending long-lived lithospheric weakness zone. © 2011 Geological Society of America.

Escosteguy L.,Institute Geologia y Recursos Minerales | Franchi M.,Institute Geologia y Recursos Minerales
Revista de la Asociacion Geologica Argentina | Year: 2010

A regional geological mapping in the Chapelco range area (Neuquén) is presented. Several volcano-sedimentary units are distinguished, related to the Cenozoic arc magmatism. The Huitrera Formation (Paleogene) is the oldest one covering the crystalline basement of the Colohuincul Complex. It constitutes the base of the Chapelco range, and it is locally associated to sedimentary rocks and basaltic flows of the Lolog Formation in the Chimehuín River area. The following cycle is composed by the mid-Miocene pyroclastic Collón Cura Formation, in the homonymous river, covered by epi- and pyroclastic deposits and basalts of the Caleufú Formation (mid-Miocene to lower Pliocene). Pliocene magmatism in the area is represented by basalts of the Tipilihuque Formation, and possibly by acidic subvolcanic stocks of Los Pinos Formation which intrudes Caleufú Fm. As a further record of Pliocene volcanism, we propose in this paper the basaltic and andesitic flows of Chapelco Formation, which compose the upper levels of Mount Chapelco. The Chapelco flows were considered by some authors as Paleogene in age. However, they unconformably overly the Huitrera Formation; as it is seen in the western slope of the Chapelco range. To the east, in the headers of Quemquemtreu River, they cover the Miocene-Pliocene Caleufú Formation. Two K/Ar ages were obtained for Chapelco Formation: 4,8 ± 0,3 y 3,7 ± 0,3 Ma (Pliocene). These flows are followed in the Mount Puntudo Grande by a basaltic volcano keeping its conical form, made up on rocks of the Chapelco Formation. The Chapelco range is therefore composed by three volcanic units: Huitrera Formation (Paleocene), Chapelco Formation (Pliocene) and Cerro Puntudo Grande Basalt (Pleistocene).

The Cerro Cóndor depocenter represents the most complete stratigraphic sequence of the continental Jurassic of the Cañadón Asfalto basin and southern South America. It is situated in extraandean Patagonia, on both sides of the middle Chubut river valley. The sedimentation in this pull-apart basin begins early in the Middle Jurassic, accompanied by effusions of olivinic basalts. The prevailing lacustrine deposits are characterized by carbonatic and siliciclastic facies associations, interfingering with volcanic deposits grading from lavic in the base to predominantly pyroclastic towards the top. The facies evolution from north to south is described, embracing the sections of farm El Torito and the canyons of Los Loros, Las Chacritas, Carrizal, Asfalto and Lahuincó. The carbonatic facies/microfacies are represented by mudstones, wackestones, packstones, grainstones and microbialitic limestones, characteristic of littoral/marginal and palustrine environments. In the Cañadón Asfalto Formation are distinguished a lower member (Las Chacritas composed by limestones, shales, sandstones and conglomerates intercalated with olivinic basalts, and an upper member (Puesto Almada) composed by tuffs, tuffites, shales and sandstones. The first is bearing a palynologic assemblage of Bajocian-Bathonian age and the second dinosaurs of Tithonian age. The stratigraphic sections of both members of the formation are described and illustrated at their type localities cañadón Las Chacritas and farm El Torito and the paleoenvironments of the depocenter, from the Aalenian to the Tithonian are described and illustrated. The age of the Puesto Almada Member at its type locality was obtained by radiometric dating (K/Ar) of biotites from a thin layer of volcanic tuff (147.1 + 3.3 Ma, Tithonian) from the upper part of the unit.

Folguera A.,Institute Geologia y Recursos Minerales | Zarate M.,National University of La Pampa | Tedesco A.,Institute Geologia y Recursos Minerales | Davila F.,National University of Cordoba | Ramos V.A.,University of Buenos Aires
Journal of South American Earth Sciences | Year: 2015

The Pampas plain (30°-41°S) has historically been considered as a sector that evolved independently from the adjacent Andean ranges. Nevertheless, the study of the Pampas showed that it is reasonable to expect an important influence from the Andes into the extraandean area. The Pampas plain can be divided into two sectors: the northern portion, adjacent to the Pampean Ranges, has been studied by Davila (2005, 2007, 2010). The southern sector (34°-41°S) is the objective of the present work. The study of this area allowed to characterize two separate foreland basins: the Southern Pampa basin and the Northern Patagonian basin. The infill is composed of Late Miocene and Pliocene units, interpreted as distal synorogenic sequences associated with the late Cenozoic Andean uplift at this latitudinal range. These foreland basins have been defined based on facies changes, distinct depositional styles, along with the analysis of sedimentary and isopach maps. The basins geometries are proposed following De Celles and Gilles (1996) taking into account the infill geometry, distribution and grain size. In both cases, these depocenters are located remarkably far away from the Andean tectonics loads. Therefore they cannot be explained with short-wave subsidence patterns. Elastic models explain the tectonic subsidence in the proximal depocenters but fail to replicate the complete distal basins. These characteristics show that dynamic subsidence is controlling the subsidence in the Southern Pampas and Northern Patagonian basins. © 2015 Elsevier Ltd.

Geuna S.E.,University of Buenos Aires | Escosteguy L.D.,Institute Geologia y Recursos Minerales | Limarino C.O.,University of Buenos Aires
Geologica Acta | Year: 2010

The magnetic properties of the Carboniferous-Permian red beds of the Patquía Formation at Punta del Viento, Sierra de Umango and some previously reported localities, all in the Paganzo Basin (Argentina) have been studied. Whereas all sites are characterized by hematite as the main magnetic carrier and a reversed-polarity magnetic remanence, we found a pattern of variation in magnetic properties along the integrated column for Patquía Formation. The Lower Member (Late Carboniferous) showed higher intensity of natural and saturation isothermal remanent magnetisation (NRM and SIRM, respectively) than the Permian Upper Member. The fall in NRM intensity from the Lower to Upper Member of the Patquía Formation may be related to a change in quantity and/ or grain-size of the hematite pigment, which may reflect the change in environmental and/or depositional setting. As for directional values of NRM, paleomagnetic poles reported for both sections are clearly different. The lower section provided a pole position coincident with Late Carboniferous poles for Gondwana, while the upper section poles are departed from the Early Permian position. We cannot decide whether the Upper Member pole is due to a primary magnetisation at 290 Ma or to a remagnetisation at ~260-270 Ma; even so, the obtained paleomagnetic pole is robust and indicates a rapid apparent polar wander in a ~30° counter clockwise rotation of the region, after deposition of the Late Carboniferous lower section, and in coincidence with the San Rafael Orogenic Phase.

Rubinstein N.A.,CONICET | Zappettini E.O.,Institute Geologia y Recursos Minerales
Ore Geology Reviews | Year: 2015

The San Rafael Massif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present. Isotopic (Sm/Nd and K/Ar) and geochemical (trace elements and REE) data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model. The fluorite deposits were formed during the Upper Triassic-Lower Jurassic as a result of the Triassic rifting that launched a hydrothermal activity at regional scale. The hydrothermal fluids had low T and high fO2 with fluorine probably derived from a mantle source and REE scavenged from the volcanics of the Gondwanan Choiyoi Magmatic Cycle upper section. The manganese deposits were formed by oxidizing hydrothermal fluids that collected Mn from deep sources and also leached REE from the upper section of the Choiyoi Magmatic Cycle during two mineralization episodes. One episode was linked to the rift tectonic setting that remained active up to the Upper Cretaceous and the other was related to an Early Miocene back-arc extensional geodynamic setting. Both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface, and can be ascribed to the general model of detachment-related deposits. © 2014 Elsevier B.V.

Giacosa R.,Institute Geologia y Recursos Minerales | Giacosa R.,National University of Rio Negro | Allard J.,National University of la Patagonia | Foix N.,National University of la Patagonia | And 2 more authors.
Journal of Iberian Geology | Year: 2014

The Pre-Andean Paleozoic substrate from the Cordillera del Viento anticline is a polyorogenic basement composed of two groups of preorogenic rocks with different stratigraphy and deformation. The oldest set consists of pre-Late Devonian metasedimentary rocks belonging to the Guaraco Norte Formation. The upper set is formed by the thick volcano-sedimentary sequence of the Carboniferous Andacollo Group. This group is composed from bottom to top of the silicic volcanic rocks of the Arroyo del Torreón Formation (early Carboniferous) and the marine sedimentary rocks of the Huaraco Formation (late Carboniferous) developed in an extensional basin. Both formations are locally separated by minor syn-extensional unconformities. The relationship between the metamorphic rocks of the Guaraco Norte Formation and the volcano-sedimentary sequence of the Andacollo Group is not observed, but we inferred a major angular unconformity associated with the Late Devonian-early Carboniferous Chanic orogeny. The main Chanic structures are tight vertical and subvertical folds with slight W-WSW vergence, formed under low-grade metamorphic conditions, with the development of a pervasive axial-plane cleavage (S1), affected by a disjunctive crenulation cleavage (S2). In the early Permian, during the San Rafael orogeny of the Gondwanan orogenic cycle, deformation occurred under very low-grade to non-metamorphic conditions. The main structures are thrusts and associated folds that are re-folded by the Cordillera del Viento anticline, related to the Andean orogeny. The WNW-oriented and SSW-vergent folds are associated with an incipient axial-plane cleavage in the pyroclastic rocks and pencil lineation in shales. The pre-Andean Paleozoic basement rocks are intruded and unconformably covered by early Permian to Early Triassic? granitoids and silicic volcanic rocks from the Huingancó volcanic-plutonic Complex (equivalent to the Choiyoi Group), establishing the beginning of the Andean orogenic cycle in this region.

Giacosa R.,Institute Geologia y Recursos Minerales | Giacosa R.,National University of la Patagonia | Zubia M.,Institute Geologia y Recursos Minerales | Zubia M.,National University of la Patagonia | And 2 more authors.
Journal of South American Earth Sciences | Year: 2010

Located in the centre of the Argentinean Patagonia between 46° and 49°S, the Deseado Region represents the foreland domain of the Southern Patagonian Andes. Its geology is characterized by thick Mesozoic sequences which, at its eastern sector, present a Mesozoic and Cenozoic geologic evolution which has been strongly determined by the development of three major tectonic phases. The present research is based on field geological mapping, interpretation of seismic and aeromagnetic data, as well as satellite image analysis. This approach has allowed us to identify and characterize the deformation that occurred throughout Jurassic, Cretaceous and Miocene times. We interpret that the most relevant structural features are the result of normal faulting generated as a response to the Jurassic rifting stage. These extensional features have strongly influenced the subsequent geometry and distribution of younger Cretaceous and Cenozoic structures.The Jurassic extensional deformation, which affected major areas of Southern Gondwana, is the product of a major intra-continental rifting stage which was accompanied by synkinematic volcanism. This tectonic regime is characterized by SW-NE directed extension that generated major oblique WNW trending faults accommodating regional dextral-extension. In the study area, this tectonic regime is inferred from the geometries of major fault systems interpreted from available seismic reflection data, as well as from the spatial distribution and orientation of the extensional fracturing associated with the opening of hybrid and dilatational siliceous epithermal Au-Ag veins.Following the Jurassic rifting stage, a more restricted Cretaceous -post-Neocomian-compressional tectonic phase took place. Throughout this period, we interpret the previously formed Jurassic extensional structures to have been reactivated under sinistral transpression. Deformation during this period generated sinistral-reverse WNW belts of deformation, which accommodated reverse faulting, imbricate thrusts, dextral and sinistral R1 and R2 shears and disharmonic folds due to a buttress effect.Under the post-Oligocene Andean regime, W-E directed compression acted on previously-formed N to NNE-oriented normal faults. Compression and shortening uplifted a series of narrow and sub-meridional ranges which run as a 200 km long inversion-related tectonic front along the Patagonian foreland. Between 47°11' and 48°40'S, one of these NNE ranges divides the entire Deseado Region into two distinctive structural domains. Whilst the western domain presents dominant NNW morphotectonic features, that to the east appears highly dominated by WNW fabrics of Jurassic and Cretaceous age.The structural features of the Eastern domain appear to extend further north of the Deseado Region towards the vicinity of the San Jorge Gulf. This WNW-trending belt hosts pre-Upper Cretaceous rocks and pre-drift basement rocks which include igneous Paleozoic metamorphic rocks and Permian to Triassic sedimentary units.The Deseado region's epithermal Au-Ag Jurassic vein systems result from the infilling and deposition of low temperature hydrothermal fluids within dilatational and hybrid structures. These spectacular vein systems are compatible with the regional SW-NE extension direction controlled by the Jurassic intra-continental rifting of southern Gondwana. Dilatational and hybrid veins are preferentially hosted by fractures in the Jurassic volcanic rocks, while the veins located within the pre-volcanic basement preferentially infill normal faults. Finally, most of these epithermal vein fields where exhumed during a moderate phase of inversion during Cretaceous times. © 2010 Elsevier Ltd.

Giacosa R.,Institute Geologia y Recursos Minerales | Giacosa R.,National University of la Patagonia | Fracchia D.,Comision Nacional de la Energia Atomica | Heredia N.,Instituto Geologico Y Minero Of Espana Igme
Geologica Acta | Year: 2012

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 72°W 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 (Dg 1) includes isoclinal and N-overturned WNW trending folds and associated thrusts, including duplexes. The second deformation phase includes NNE trending open folds (Dg 2). 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 SubAndean 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, Dg 1, Gondwanan structural fabric.

Loading Institute Geologia y Recursos Minerales collaborators
Loading Institute Geologia y Recursos Minerales collaborators