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Construcción de McCoss (1986) para la veta Don Gregorio. Referencias: (X) dirección de mayor extensión, (S) vector de desplazamiento (dirección de apertura de la fractura de extensión).
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Se describen las características geométricas y cinemáticas de las estructuras que se observan en la región de Los Menucos, en la parte norte del macizo nordpatagónico, caracterizada por extensos afloramientos de rocas volcánicas e intrusivas y sedimentarias del Triásico. Estas estructuras son fallas de rumbo O-E, cuyas longitudes superan los 120 km...
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... A partir del tercio oriental de la Hoja y hacia el este, estos relieves ya no pueden reconocerse y cobran importancia las geoformas asociadas con extensos flujos basálticos. Al N y NE, en la región de La Angostura-Coli Toro, Los Menucos y La Esperanza vuelven a definirse algunos relieves estructurales de menor magnitud asociados a fallas kilométricas de rumbo O-E y cinemática dextral (Cucchi et al. 2001, Giacosa et al. 2007, las que pueden reconocerse hasta el mismo borde septentrional del Macizo Nordpatagónico en los granitoides triásicos de Curacó (Mizerit et al. 2014) y sobre la margen sur del río Negro, donde controlan las acumulaciones iniciales del Grupo Cuyo (Roberts . ...
... (c) A partir del Jurásico y en relación con el rifting continental, la formación de nuevos y mayores depocentros volcano-sedimentarios, controlados por fallas de cinemática normal y normal-oblicua, muchas de ellas a partir de heterogeneidades previas. Este régimen, de orientación general SO-NE, estuvo presente en toda la región y en la cuenca Neuquina , Cristallini et al. 2009, Franzese et al. 2006, 2007, Benedini et al. 2014, Giacosa et al. 2007y Mizerit et al. 2014, entre otros), y condicionó las subsiguientes fases contraccionales. (d) La deformación contraccional Patagonídica, cuyos efectos se observan en las discordancias angulares, pero que en relación con la formación de relieves resulta difícil de cuantificar. ...
González, P., Giacosa, R., Franchi, M., Dalponte, M., Hernando, I., Aguilera, Y., Coluccia, A. 2024. Hoja geológica 4169-III Ingeniero Jacobacci. 143 pp. (Boletín, N° 311). Buenos Aires, Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales. ISSN 0328-2333.
Esta contribución está compuesta por un mapa geológico a escala 1: 250.000 de la zona de Ingeniero Jacobacci y sus alrededores, en el norte de la Patagonia (41°00’-42°00’ S / 69°00’-70°30’ O, provincia de Río Negro, Argentina), que cubre alrededor de 13.840 km2, y por un texto explicativo donde se presenta la estratigrafía de la región y la caracterización de las unidades aflorantes, los rasgos estructurales que las afectaron, las peculiaridades de las geoformas, una reseña de los recursos minerales con que cuenta el área y los sitios de interés geológico relevantes.
... The Permian to Middle Triassic magmatism and its associated sedimentation have been assigned to the La Esperanza Complex and Los Menucos Group Falco et al., 2020). These units are separated by an E-W-oriented regional structure called the Cerro Piche Fault (Giacosa et al., 2007). To the north of this fault, plutons, dikes, and lavas with ages between 273 and 244 Ma were assigned to the La Esperanza Complex, interpreted as a shallow composite and pulsatory, multi-sourced, open magmatic system (Pankhurst et al., 2006;Martínez Dopico et al., 2017Luppo et al., 2019). ...
The Upper Triassic magmatic and tectonic evolution of the central North Patagonian Massif is evaluated on the basis of the zircon U–Pb-Hf record and whole-rock geochemistry for volcanic rocks of the Los Menucos area. The sample analyzed on this study yields a 210 ± 3 Ma U–Pb zircon age, and the geochemical data for the Upper Triassic rocks are indicative of a high-K calk-alkaline arc-type magmatism, which also has adakitic signature related to melting of the subducted oceanic slab. In addition, the Hf isotope data for zircon from this sample, with ƐHf(T) values between −6.1 and −8.7, support a mixed source that may have involved melted slab and crustal reworking. The emplacement of the Upper Triassic magmatism far into the central North Patagonian Massif precedes a ca. 24 Ma stage of magmatic quiescence, which likely represents a crustal-shortening period related to a horizontalized subduction. Our interpretation of the Upper Triassic – Lower Jurassic magmatic and tectonic evolution of northern Patagonia is in agreement with the hypothesis of Upper Triassic South Gondwanian flat-slab, which shifted the magmatic arc towards the continental interior at a time of crustal shortening and with arc-type adakitic magmatism. The Lower Jurassic magmatic record is consistent with slab detachment and later roll-back, which would have promoted crustal extension and intraplate magmatism, and also shifted the arc magmatism to the paleo-trench. As a consequence of this stage, the Subcordilleran and North Patagonian batholiths were emplaced. The progressively less negative Hf isotope signature for magmatic zircons is consistent with addition of more basic magmas generated throughout the Jurassic. The Upper Triassic-Middle Jurassic magmatism in northern Patagonia was part of a complex tectonic evolution, which involved crustal shortening and extension during plate reorganization on the critical period og the break-up of Gondwana supercontinent.
... The mainly volcanic LMC lies on pre-Permian metamorphic rocks and Permian granitoids and is covered by Upper Cretaceous sedimentary rocks and Paleogene to Neogene basalts (Cucchi et al., 2001;Labudía and Bjerg, 2001;Lema et al., 2009) (Fig. 2C). In the Los Menucos area, the succession, about 2000-3000 m thick (Lema et al., 2009), is exposed through a SE-plunging synclinal, the Piche synform (Giacosa et al., 2007) (Fig. 2C). The succession mainly comprises acidic (rhyolitic-dacitic) pyroclastic deposits with minor intercalations of volcanogenic clastic beds and andesitic lava flows (Labudía and Bjerg, 2001;Lema et al., 2009;Falco et al., 2020). ...
The Los Menucos Complex (North Patagonian Massif, Río Negro province, Argentina) has been long regarded as Late Triassic in age. A Dicynodontipus-dominated record is historically known from this complex and particularly from the Puesto Tscherig locality. Here we report the Puesto Vera site, where a new track-bearing horizon was discovered within a 73-m-thick volcano-sedimentary succession. Footprints from this site are morphologically similar to those from Puesto Tscherig and resemble footprints classically referred to the ichnogenus Dicynodontipus, thus we assigned the new material to Dicynodontipus isp. The new ichnological material is age constrained to a time interval between the Changhsingian (Lopingian, Permian) and the Olenekian (Early Triassic), on the basis of recently obtained U–Pb radiometric datings from two ignimbrites, respectively at the base and top of the Puesto Vera stratigraphic section. Interestingly, the Dicynodontipus record from the Los Menucos Complex is older than previously supposed. The inherent chronostratigraphy is consistent with the temporal occurrence of the ichnotaxon, which to date has a global distribution spanning from the Wuchiapingian (Lopingian, Permian) of northern Italy to the early Middle Triassic of Germany. Taking into account the most recent datings as well as previous literature about the geology and paleontology of Los Menucos, the new age-constrained finding turns out to encompass the Permian–Triassic transition and mirror a tetrapod fauna dwelling in a mid-latitude, highland paleoenvironment of southwestern Gondwana.
... The best exposures of the CPG are delimited to its eastern sector of the graben by the Queupuniyeo Range, and to the west by the Bajos Hondos Basaltic Plateau (Fig. 2). This tectonic structure, also mentioned as Piche Fault System or pull-apart Piche (Giacosa et al., 2007), is part of a major family of E-W faults recognized in the surrounding area, such as the Loma Blanca fault (Cucchi et al., 2001), as well as the La Laja and La Laja Norte faults (Giacosa et al., 2007), inter alia. ...
... The best exposures of the CPG are delimited to its eastern sector of the graben by the Queupuniyeo Range, and to the west by the Bajos Hondos Basaltic Plateau (Fig. 2). This tectonic structure, also mentioned as Piche Fault System or pull-apart Piche (Giacosa et al., 2007), is part of a major family of E-W faults recognized in the surrounding area, such as the Loma Blanca fault (Cucchi et al., 2001), as well as the La Laja and La Laja Norte faults (Giacosa et al., 2007), inter alia. ...
... The Los Menucos Group or Complex and its stratigraphy are still under debate (see Falco et al., 2020 and references therein). Initially, the volcanic and sedimentary succession of the CPG was considered the lowermost part of the Los Menucos Group (Labudía and Bjerg, 2001) or Los Menucos Complex (Giacosa et al., 2007). Recently, Falco et al. (2020) reviewed the stratigraphy and proposed a subdivision for the Los Menucos Group (after Labudía and Bjerg, 2001) into a series of ignimbrites, mesosilicic lavas and sedimentary layers that were emplaced during the interval of 253 to 248 Ma. ...
The volcano-sedimentary succession of the Cerro Piche Graben, Río Negro province, Patagonia (Argentina), was studied U–Pb and Lu–Hf in zircon. As well, a stratigraphic, sedimentological, palynology and a review of the paleo flora content was made. The combined stratigraphic and geochronological study on the volcano-sedimentary succession indicates that the Cerro Piche Graben was developed during the Early Jurassic and allow us to propose the Cerro Piche Formation. This formation is composed of a lower volcanic succession (named the Loma Blanca Member) that is restricted to the tectonic depression and that was probably emplaced during the Sinemurian (ca. 191 Ma), and an upper sedimentary succession (named the El Tono Member) that was unconformably deposited over the lower sequence during the Pliensbachian (ca. 183 Ma). The sedimentological study of the upper sequence allows to recognition of nine sedimentary cycles related to the evolution of an alluvial fan. The palynofacies interpretations reflect intermittent exposure to weathering and/or intense reworking of organic components as a result of a dynamic sedimentary system with a high terrestrial input, sediment reworking, and/or intermittent subaerial exposure. The paleoflora preserved in this sedimentary succession is composed exclusively of conifers and assigned to Cupessinoxylon sp., and probably corresponds to an arboreal paleocommunity. The U–Pb data on Early Jurassic detrital zircon grains from the El Tono Member indicate a maximum depositional age (MDA) of 185 Ma for this sequence, and the Lu–Hf data support a reworked continental crust for the zircon source. . Additionally, the U–Pb and Lu–Hf data obtained during this work together with data from the North Patagonian Massif supports the recognition of four magmatic cycles, called C0, C1 (including C1i source), C2 and C3. The C1 (172–180 Ma) and the C3 (155–162 Ma) cycles indicate mixing of juvenile mantle-derived and reworked crustal components in the parental magma of zircons and the C0 (182–192 Ma) cycle, which includes the distal volcanism identified in the Cerro Piche Graben, the C1i (172–180 Ma) and C2 (166–169 Ma) cycles seemingly represent three episodes of crustal reworking.
... The first variation in the extensive dike pattern and the associated volcanism occur southward the trace of the Fita Ruin Canyon (Fig. 12B). The Canyon located at 40º39ꞌ parallel in the Río Negro Province forms an E-W elongated valley which extension could be traced in continuity with the Loma Blanca dextral fault recognized in La Esperanza area (Corbela, 1975;Giacosa et al. 2007). Fault continuity progresses westward along more than 150 km. ...
... The faults kinematics was regionally described 40 km NW of Los Menucos town (Giacosa et al. 2007), which affected the metasediments of the Lower ...
The early Jurassic volcanism of Central Patagonia covers an extensive area of 50,000 km² where the volcanic deposits occur as isolated systems. The volcanic records form an elongated belt in which the composition, depositional and genetic features, show several differences along with its distribution. The Cañadón Chileno Complex (CCHC), located in the Río Negro province, provides the opportunity to evaluate and improve the knowledge about the Lower Jurassic volcanic stratigraphy and the lower Jurassic regional setting of Central Patagonia.
Based on the field and laboratory data developed in the present work, 22 lithofacies were recognized and grouped into eight facies associations. The continental sedimentary environments include alluvial fan deposits (FA 1), ephemeral deposits (FA 2), braided fluvial deposits (FA 3), alluvial plains, or over banks (FA 4), and lacustrine deposits (FA 9). On the other hand, the pyroclastic facies were separated according to the pyroclastic currents involved during the deposition; into fall-out, dilute, and density currents (FA 5, FA 6, and FA 7). Effusive andesitic feeders and lava-flows (FA 8) were also recognized.
The stratigraphic data obtained in the present work allow proposing the existence of two felsic diatreme volcanoes in the CCHC records - described here as Southern and Northern Zone-, developed over a local subsided area, represented by an asymmetrical basin.
Seven units were recognized and described in the CCHC (Units a, b, c, d, e, f, and g: unit (a) represents an initial stage of continental sedimentation recorded throughout the entire Complex. Unit (b) represents the upper felsic diatreme facies, in Southern Zone of the Complex, where debris flows are interbedded with massive lapilli-tuff deposits. Unit (c) consists of local andesitic lavas flows and feeder dikes, and the unit (d) consists of welded lapilli tuff deposits interpreted as the growth of the volcanic system. The Northern Zone evolves similarly with the felsic intra-diatreme deposits of unit (e). The unit (f) consisting of an effusive stage represented by extended andesitic lava flows. Finally, a deep lacustrine system is installed (unit g) that includes shallow and deep facies, with intercalations of local pyroclastic deposits.
Also, new geochronological data (U-Pb zircon age of 188 ± 3 Ma) was determined to confirm and reinforce the correlation criteria between the different volcanic areas in Central Patagonia, indicating that the volcanism described here is synchronous with the Northern silica-rich calderas of the Garamilla Formation as well as the large andesitic volcanoes of the Lonco Trapial Formation located southward to the CCHC. The regional volcanism changes described, in the present work, are connected with the N-S rift segment limited by E-W regional transfer fault systems developed in continuity to the strike-slip structures of the La Esperanza area.
... This area lacks precise geochronological information, being the closest measured point in the Cerro de Las Minas, located 5 km west, of 211 ± 1 Ma, Norian in age . From a structural point of view, the Piche synform (Giacosa et al., 2007) Far from radiometric dating failures, these age discrepancies allow us to infer a hiatus between Changhsingian-Olenekian to Middle-Late Triassic aged deposits. In this regard, it is possible to assess the existence of two allounits separated by discontinuities. ...
... The upper Permian-Triassic volcanogenic rocks from the North Patagonian Massif, such as the Los Menúcos Complex (Llambías and Rapela, 1984;Rapela and Llambías, 1985;Cucchi et al., 2001;Falco and Hauser, 2017;Luppo et al., 2018) and Treneta and Puesto Piris formations (Rapela and Caminos, 1987;Caminos, 2001) and correlative volcanic units (González et al., 2016 rest unconformably onto the continental basement deformed by the early-middle Permian Gondwanide orogeny . Emplacement of these units would take place in an extensional context with an NE-SO main stretching direction (Giacosa et al., 2007;González et al., 2016). Farther west, in the southern region of the Neuquina Basin, Upper Triassic intermediate to acidic volcanic and pyroclastic rocks were deposited in an extensional retroarc basin (D'Elia et al., 2012). ...
... In this work, we present SHRIMP U-Pb zircon data and paleomagnetic results for Permian-Triassic dikes and volcanic units of the La Esperanza Plutono-Volcanic Complex (Llambías and Rapela 1984;Martínez Dopico et al. 2017b), exposed in the La Esperanza area, located in a central area of the northern sector of NPM (Fig. 1a). This area is ideal to carry out a paleomagnetic study in Late Paleozoic-to-Triassic rocks, because it has not suffered a significant tectonic activity since Triassic times (Giacosa et al. 2007). ...
A paleomagnetic and geochronologic study was carried out on Late Permian-to-Early Triassic magmatic units exposed in the North Patagonian Massif, near the locality of Estancia La Esperanza (Río Negro Province, Argentina), to provide better paleogeographic and tectonic constraints on the evolution of Patagonia and its relations with Gondwana in the Late Paleozoic–Early Mesozoic. The study included the Late Permian (264 ± 2 Ma) Rhyolite Dome, the Collinao Dacite, for which we obtained a U–Pb zircon crystallization age of 253 ± 2 Ma, several basic dikes, that intrude older granite units (255 ± 2 Ma), and a swarm of acidic dikes for which an Early Triassic age had been previously assigned that we confirmed with a U–Pb zircon age of 244 ± 2 Ma. A paleomagnetic pole (C), computed on the basis of seven VGPs, was obtained for the Collinao Dacite and associated units (48.3°S, 349.9°E, N = 7, A95 = 15.1°). A single VGP for the somewhat older Rhyolite Dome falls close to that pole. A second paleomagnetic pole (A) which strongly disagrees with the C position was computed based on 12 VGPs from the same number of acidic dikes (87°S, 51.5°E, N = 12, A95 = 8.1°). The basic dikes, with ages bracketed between the dacitic and the rhyolitic dikes, yielded four VGPs, two of which are consistent with the C pole and the other two are close to the A pole. The C pole falls on a much older position (Late Carboniferous) on different Gondwana/South America reference paths, which is clearly anomalous based on its Late Permian age. The A pole, in turn, is consistent with the 250/240 Ma paleomagnetic poles in most reference paths for Gondwana/South America. Either regional tilting or rotation around a vertical axis to explain the anomalous C pole is unlikely considering the local geological evidence. A working model is presented to explain the discrepancy as due to around 30° CCW rotation of the whole North Patagonian Massif during the latest Permian and earliest Triassic, closing a V-shaped basin that separated it from southern Gondwana, as the final stages of collision of an allochthonous or para-autochthonous Patagonia terrane. This hypothesis is consistent with Late Permian-to-Early Triassic evidence of deformation in the Hespérides Basin as well as in northern Patagonia. Scarce previous paleomagnetic data from this region can be reconciled with this model, considering that they are very loosely constrained in age.
... Our study was carried out in a 500 km 2 area located between La Esperanza ranch and Los Menucos town ( Fig. 1) where LMC ( Lema et al., 2008) displays one of the best preserved and thickest volcanic accumulations. A geologic survey and paleomagnetic systematic sampling (work in progress) was carried out along W-E and N-S sections, respectively located along the western and eastern flanks of a major structure referred as the "Piche Synform" by Giacosa et al. (2007). This is characterized by a NW-SE axis smoothly plunging to the SE ( Fig. 2). ...
The Los Menucos Complex (northern Patagonia) consists of ~6 km thick succession of acidic and intermediate volcanic and pyroclastic products, which has been traditionally assigned to the Middle/Late Triassic. New U/Pb (SHRIMP) zircon crystallization ages of 257 ± 2 Ma at the base, 252 ± 2 Ma at an intermediate level and 248 ± 2 Ma near the top of the sequence, indicate that this volcanic event took place in about 10 Ma around the Permian-Triassic boundary. This volcanism can now be considered as the effusive terms of the neighboring and coeval La Esperanza Plutono-Volcanic Complex. This indicates that the climax of activity of a large magmatic province in northern Patagonia was coetaneous with the end-Permian mass extinctions. Likely correlation of La Esperanza- Los Menucos magmatic province with similar volcanic and plutonic rocks across other areas of northern Patagonia suggest a much larger extension than previously envisaged for this event. Its age, large volume and explosive nature suggest that the previously ignored potential role that this volcanism might have played in climatic deterioration around the Permian-Triassic boundary should be investigated.
... The main body of the Donosa Granite has a N-S elongated rhombic shape with N 50 km 2 of outcrops, its borders being remarkably rectilinear suggesting a fault system constraining shape and distribution of the pluton. This was later disrupted by E-W dextral transcurrent faults (Late Triassic and/or Jurassic, Giacosa et al., 2007). The restoration of movement along these transcurrent faults shows that the main body of the Donosa Granite extends along a NW-SE direction, parallel to its borders as well as to the macroscopic (K-feldspar alignment) and shallowly plunging linear magnetic fabrics. ...
Two main lines of evidence disagree whether or not the Patagonian blocks collided with Gondwana. All models invoke the voluminous magmatism of the La Esperanza Complex as evidence for active subduction magmatic arc or to a postcollisional setting. The evolution of this bimodal igneous suite is reassessed with field, geochronological (SHRIMP U-Pb zircon and K-Ar mica) and petrophysical data. Emplacement of high-K calk-alkaline granitic magmas occurred at shallow crustal levels (2–8 ± 2 km depth) related to the development and collapse of a caldera associated with a regional NW-SE structural trend. Magmatism involved intermediate hybrid pulses at 273 ± 2 Ma and 255 ± 2 Ma (Prieto Granodiorite) that shifted like a yo-yo to acidic magmas at 260 ± 2 Ma and 250 ± 2 Ma (Donosa and Calvo granites). Absence of solid-state deformation features and the low anisotropy degrees in the granites indicate that its fabric is magmatic in origin. Magnetic fabric in granodiorites displays a concentrical pattern with subhorizontal foliations and lineations. Parallel to the volcanic axis, magnetic foliations and moderately plunging lineations indicate a common feeder system for plutonics and volcanics. Donosa Granite shows a discordant pattern with WNW-ESE ENE-WSW trending low plunging lineations and foliations. The plutono-volcanic system construction (273–255 Ma) followed NW-SE and NE-SW diamond shape faults trends and supracrustal discontinuities. Magmatic Climax is bracketed at 260 Ma. The collapse of the edifice is evidenced by the intrusion of acid magma plugs and dike swarms between 250 and 246 Ma. A similar age range was identified in other areas of Patagonia related to syn and postcollisional tectonic events. No evidence of tectonic activity such as major uplift, metamorphism or thrusting was found excepting regional strike-slip faulting and extension. Therefore, La Esperanza Complex is a high crustal level episode, and as such may not have structurally recorded an active collision during its crystallization and cooling.
