La cuenca de antepais terciaria asociada a la faja plegada y corrida de los Andes Patagónicos entre los 41º y 42º S, SO de Argentina

In Argentina, between 41"-42" S and related to the Andean Patagonian fold and thrust belt, two synorogenic sedimentary sequences were deposited in the Tertiary foreland basin. They represent different moments of the eastward migration of the orogenic front, during upper Eocene to Mio-Pliocene times. The units within the sequence have a characteristic wedge shape, and the proximal facies on the west, prograde to the east and cover the lower distal-medium facies. Structural relationships diplay discordant boundanes near the active orogenic front, which progressively change to concordant towards the foreland. Eocene-Oligocene volcano-sedimentary basa1 sequence contains marine intercalations with Pacific affinities, while Oligocene-lower Pliocene upper sequence has a sedimentary-pyroclastic composition. Based on the age and geometrical characteristics, we proposed a preliminary correlation between proximal to distal facies in the synorogenic formations, and the well known litostratigraphic units outcropping in the El Bolsón valley and the Ñirihuau-Collón Cura basin

Vacuum Properties of Mesons in a Linear Sigma Model with Vector Mesons and Global Chiral Invariance

We present a two-flavour linear sigma model with global chiral symmetry and vector and axial-vector mesons. We calculate pion-pion scattering lengths and the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated that vector and axial-vector meson degrees of freedom play an important role in these low-energy processes and that a reasonable theoretical description requires globally chirally invariant terms other than the vector meson mass term. An important question for meson vacuum phenomenology is the quark content of the physical scalar f0(600) and a0(980) mesons. We investigate this question by assigning the quark-antiquark sigma and a0 states of our model with these physical mesons. We show via a detailed comparison with experimental data that this scenario can describe all vacuum properties studied here except for the decay width of the sigma, which turns out to be too small. We also study the alternative assignment f0(1370) and a0(1450) for the scalar mesons. In this case the decay width agrees with the experimental value, but the pion-pion scattering length $a_{0}^{0}$ is too small. This indicates the necessity to extend our model by additional scalar degrees of freedom.Comment: 22 pages, 6 figure

Study of chiral symmetry restoration in linear and nonlinear O(N) models using the auxiliary field method

We consider the O(N) linear {\sigma} model and introduce an auxiliary field to eliminate the scalar self-interaction. Using a suitable limiting process this model can be continuously transformed into the nonlinear version of the O(N) model. We demonstrate that, up to two-loop order in the CJT formalism, the effective potential of the model with auxiliary field is identical to the one of the standard O(N) linear {\sigma} model, if the auxiliary field is eliminated using the stationary values for the corresponding one- and two-point functions. We numerically compute the chiral condensate and the {\sigma}- and {\pi}-meson masses at nonzero temperature in the one-loop approximation of the CJT formalism. The order of the chiral phase transition depends sensitively on the choice of the renormalization scheme. In the linear version of the model and for explicitly broken chiral symmetry, it turns from crossover to first order as the mass of the {\sigma} particle increases. In the nonlinear case, the order of the phase transition turns out to be of first order. In the region where the parameter space of the model allows for physical solutions, Goldstone's theorem is always fulfilled.Comment: 25 pages, 9 figures, 1 table, improved versio

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

Stratigraphy, structure and geodynamic evolution of the Paleozoic rocks in the Cordillera del Viento (37º S latitude, Andes of Neuquén, Argentina)

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.El sustrato paleozoico pre-andino que aflora en el anticlinal de la Cordillera del Viento, es un basamento poliorogénico que está com­puesto por dos conjuntos de rocas preorogénicas con estratigrafía y condiciones de deformación diferentes. El más antiguo tiene una edad devónica superior y está formado por las rocas metasedimentarias de la Formación Guaraco Norte, en tanto que el conjunto superior son las espesas acumulaciones volcano-sedimentarias carboníferas del Grupo Andacollo. Este grupo, integrado en su parte inferior por rocas volcánicas silíceas de la Formación Arroyo del Torreón (Carbonífero inferior) y hacia techo, por las sedimentitas clásticas marinas de la Formación Huaraco (Carbonífero superior) fue desarrollado en el marco de una cuenca extensional y pueden estar separadas localmente por discordancias menores de carácter sin-extensional. Las relaciones entre las rocas metamórficas y la secuencia volcano-sedimentaria del Carbonífero no se observan, pero se infiere una discordancia mayor asociada con la orogenia Chánica, que tuvo lugar entre el Devónico Superior y el Carbonífero inferior. Las estructuras chánicas están asociadas a un metamorfismo de bajo grado y son pliegues apretados sub-verticales a verticales y con ligera vergencia al O-OSO que llevan asociados un clivaje penetrativo (S1) de rumbo N-S a NNO que está afectado por un clivaje subvertical más espaciado (S2). En el Pérmico inferior, durante la orogenia San Rafael del ciclo orogénico Gondwánico, la deformación contraccional se produce en condiciones de metamorfismo de muy bajo grado o en ausencia de éste. Las estructuras principales son cabalgamientos y pliegues asociados que se encuentran plegados por el anticlinal ándico de la Cordillera del Viento. Los pliegues de rumbo ONO y vergencia al SSO llevan asociados un incipiente clivaje de plano axial en los contactos entre limolitas y volcanitas y lineación de tipo lápiz (pencil) en las lutitas. Las rocas del basamento paleozoico pre-ándico están intruidas y cubiertas discordantemente por rocas volcánicas silíceas de edad Pér­mico inferior a Triásico Inferior?, correspondientes al Complejo volcánico-plutónico Huingancó (equivalente al Grupo Choiyoi), unidad que marca el comienzo el ciclo orogénico Andino, en esta región

Two chiral nonet model with massless quarks

We present a detailed study of a linear sigma model containing one chiral nonet transforming under U(1)$_A$ as a quark-antiquark composite and another chiral nonet transforming as a diquark-anti diquark composite (or, equivalently from a symmetry point of view, as a two meson molecule). The model provides an intuitive explanation of a current puzzle in low energy QCD: Recent work has suggested the existence of a lighter than 1 GeV nonet of scalar mesons which behave like four quark composites. On the other hand, the validity of a spontaneously broken chiral symmetric description would suggest that these states be chiral partners of the light pseudoscalar mesons, which are two quark composites. The model solves the problem by starting with the two chiral nonets mentioned and allowing them to mix with each other. The input of physical masses in the SU(3) invariant limit for two scalar octets and an "excited" pion octet results in a mixing pattern wherein the light scalars have a large four quark content while the light pseudoscalars have a large two quark content. One light isosinglet scalar is exceptionally light. In addition, the pion pion scattering is also studied and the current algebra theorem is verified for massless pions which contain some four quark admixture.Comment: 22 pages, 8 figure

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