Erosion Surface and Granitic Morphology in the Sierra de Lihuel Calel, Province of La Pampa, Argentina

Fil: Aguilera, Emilia Yolanda. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Sato, Ana María. Centro de Investigaciones Geológicas (CIG). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Llambías, Eduardo Jorge. Centro de Investigaciones Geológicas (CIG). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Tickyj, Hugo. Departamento de Ciencias Naturales. Facultad de Ciencias Exactas y Naturales. Universidad Nacional de La Pampa; Argentin

Paleo-landscapes of the Northern Patagonian Massif, Argentina

Fil: Aguilera, Emilia Yolanda. Instituto de Geomorfología y Suelos (IGS). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Rabassa, Jorge. Laboratorio de Geomorfología y Cuaternario. CADIC. Universidad Nacional de Tierra del Fuego; ArgentinaFil: Aragón, Eugenio. Centro de Investigaciones Geológicas (CIG). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Pseudokarst and Speleothems in the Chihuido Granite, Province of Mendoza, Argentina

The core of the Chihuido Anticline is located precisely at Cerro Chihuido, Malargüe, southern Mendoza province, Argentina. This anticline represents the outcropping pre-Jurassic platform of the margin of the Neuquén Basin, which is composed of three volcano-sedimentary units separated by angular unconformities. The older unit corresponds to the volcano-sedimentary complex named as El Fortín, which concludes with the intrusion of a thick rhyolite-monzogranite dyke. The dyke, together with plutons corresponding to the Gondwana magmatism, is exposed on a paleosurface whose relief has been partly fossilized by much modern pyroclastic rocks. The thickness of the dyke varies from 0.2 km to almost 1 km. In this landscape, the dyke is the most remarkable topographic and geological characteristic, not only for its huge dimensions but als o for its numerous weathering cavities that provide it with a quite peculiar aspect. Typical pseudokarst landforms are represented by tafoni cavities. The nature of pseudokarst is portrayed by selective erosion along joint planes and andesite composition blocks included in the dyke. In the wall of some cavities within the almost vertical dyke, opal speleothems have been formed from silica released by rock weathering. The speleothems were studied by means of optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction. The study of these minor features of the granitic landscape, such as tafoni, and the associated speleothems, the description of their morphology, and the analysis of their composition are the main objectives of this chapter.Fil: Aguilera, Emilia Yolanda. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Carretero, Silvina Claudia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rabassa, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin

The Miocene Magmatism in the Malargüe and Chos Malal Fold and Thrust Belts

Late Oligocene to Pliocene magmatism at the latitudes of Malargüe and Chos Malal fold and thrust belts, in Neuquén basin, is distributed from the main Andean axis to the retroarc zone. While arc magmatism maintained relatively similar compositional and geochemical features during late Oligocene to Pliocene times, major variations are seen in volcanic sequences developed in the retroarc zone, due to the development of the shallow subduction regime by mid-late Miocene times. Thus, late Oligocene-early Miocene period is characterized by an extensional regime that conditioned mainly tholeiitic magmas in the main Andean axis and alkaline, intraplate magmas in the retroarc zone. Early-late Miocene marks a change to more compressional tectonics in the Andean margin. Main arc magmatism showed a change to clearer arc, calc-alkaline signature, while retroarc magmatism showed the progressing input of slab-derived products as the shallow subduction regime triggered the eastward migration of the asthenospheric wedge. Thus, arc-derived lavas expanded into the mid to far retroarc zone (~69°30? to 68°30?) with arc-like andesitic to dacitic compositions.With the progressive influence of the shallow subduction regime, arc-derived products reached almost 500 km away from the Chilean trench at ∽36°S by latest Miocene-Pliocene. By middle Pliocene, re-steepening of the slab conditioned extensional tectonics that favored a widespread alkaline volcanism in the present-day Payenia retroarc and rhyolitic calderas main arc zone. After ∽3.5 Ma, retroarc magmatism at the latitudes of the Malargüe and Chos Malal fold and thrust belts lack of clear arc-related geochemical features.Fil: Litvak, Vanesa Dafne. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Iannelli, Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Fernández Paz, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentin

Late Cretaceous to Oligocene Magmatic Evolution of the Neuquén Basin

Geochemical variations in arc- and within-plate magmatic associations since Late Cretaceous times are analyzed and correlated with the main tectonic changes that influenced the Neuquén Basin evolution. The collision and southward migration of the Farallon-Aluk mid-ocean ridge along the Chilean trench since 80 Ma have played an important role in controlling the Late Cretaceous to Oligocene magmatic evolution of the arc and retroarc zones. The passage of this spreading center through the Chilean trench induced the development of geochemically distinct magmatic associations since Late Cretaceous to Eocene times associated with the extensional reactivation of the Cretaceous fold and thrust belt. Then, by Late Oligocene times, a major plate tectonic reorganization occurred when the Farallon plate broke apart and the resulting Nazca plate started an orthogonal subduction regime beneath the South American plate with higher convergence rates. Then extensional basins and associated magmatism developed at this time destabilizing the Paleogene fold and thrust belt and establishing a more homogeneous tholeiitic signature along the Andean axis.Fil: Iannelli, Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Fennell, Lucas Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Fernández Paz, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Litvak, Vanesa Dafne. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Encinas, Alfonso. Universidad de Concepción; ChileFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

A Provenance Analysis from the Lower Jurassic Units of the Neuquén Basin. Volcanic Arc or Intraplate Magmatic Input?

A possible signal of the Jurassic Chon Aike Igneous Province within the early infill of the Neuquén Basin is recognized in our provenance analyses. We use a combination of detrital zircon geochronology and Lu-Hf isotope analysis, along with sandstone petrography descriptions to characterize the sediments source region in the Cuyo Group. The sandstone petrographic analysis confirms important contributions from volcanic sources of different compositions. U-Pb ages and Hf isotopes obtained in the analyzed zircons indicate a more complex configuration given by multiple igneous components. The variations in the provenance patterns allow us to make some observations about the paleogeographic evolution of the basin. At the base of the sequence, the sediments were derived from local sources composed of Permian basement and Upper Triassic volcanic rocks, whereas in the top, the zircons were supplied from Lower Jurassic volcanic rocks and Lower Paleozoic and Precambrian basements suggesting more distal and ancient sources. Low values of εHft (-15.5 to -0.7) analyzed in Permian and Triassic detrital zircons indicated an evolved source with strong crustal contribution. This data is in agreement with the negative values of εHft and εHft calculated in Permian and Triassic igneous rocks from the North Patagonian Massif. The Hft about -4 of the Jurassic detrital zircons indicated a crustal origin for the source rocks and are clearly compatible with the isotopic compositions of the Chon Aike Igneous Province. A volcanic source region compatible with the Andean arc is dismissed because the Jurassic arc has isotope characteristics of a mantle source.Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Garcia Morabito, Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Manassero, Marcelo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Valencia, Victor. University of Washington; Estados UnidosFil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

The Structure of the Southern Central Andes (Chos Malal Fold and Thrust Belt)

The Chos Malal fold and thrust belt, formed during the Andean orogeny, is characterized by the involvement of both the Paleozoic basement and Mesozoic strata of the Neuquén Basin into the deformation. Two detailed structural cross sections, built based on previous field mapping, new subsurface interpretations, and seismic and borehole data, allow characterizing the structural style of this orogenic belt. A close interaction between large thick-skinned structures (first order) and complex thin-skinned structures (second, third, and fourth order), related to the presence of multiple detachments in the sedimentary cover, is recognized. The largest thrusts form basement-involved duplex structures, with a lower detachment located at a depth of about 12–14 km and an upper detachment in the Jurassic evaporites of the Auquilco Formation. Displacement transmitted by these basement sheets in the inner zone of the Chos Malal fold and thrust belt produces a wide region of thin-skinned deformation, which contains second-order fault-bend folds that transfer deformation to the overlying Agrio Formation shales (Early Cretaceous) giving rise to third-order folds and thrusts involving this unit. In the outer zone, the basement-involved thrusts have less displacement and form monoclines and a complex thin-skinned deformation restricted to the deformation front, possibly caused by buttressing effect exerted by the overlying Miocene volcanic sequences. This impediment in forward deformation leads to an important out-of-sequence faulting, whose displacement is compensated by a passive-roof backthrust along the Cretaceous evaporites of the Bajada del Agrio Group forming a triangle zone. Second-order anticlines under this triangle zone, where the seismic data are of low quality, constitute important hydrocarbon oil fields such as El Porton and Filo Morado. Understanding the close relationship between the structures of different order cropping out in the inner zone of the Chos Malal fold and thrust belt is important to interpret the subsurface structures forming hydrocarbon oil fields in the outer zone as well as to identify other complex structures that may lead to new exploration opportunities. Restitution of the structural cross sections allowed calculating a tectonic shortening for this region in the order of 22–25 km (16–18%), higher than estimated by previous authors who generally simplified the thin-skinned deformation and considered the tectonic inversion of normal faults as the main mechanism of deformation in this orogen.Fil: Turienzo, Martin Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Sánchez, Natalia Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Lebinson, Fernando Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Dimieri, Luis Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentin

Fluid evolution in a volcanic-hosted epithermal carbonate–base metal–gold vein system: Alto de la Blenda, Farallón Negro, Argentina

ISSN:0026-4598ISSN:1432-186