The Copahue-Pino Hachado high and the Loncopuè trough: An episodic tectonic behaviour, Neuquén Andes (37°-39°S)

The Andes located in the central Neuquén (38°-39°S), which belong to the southern Central Andes (35°-39°S), have recorded a similar chronology of uplift than the neighbor northern Patagonian Andes (39°-46°S), Both areas have been formed trough successive phases of contraction in the Late Cretaceous, Middle Eocene and Late Miocene respectively. However, the Neuquén Andes have experienced two discrete phases of orogenic relaxation, during the Late Oligocene and Pliocene-Quaternary, which make then distinctive respect to the area located to the south. Field studies have shown new evidences of an episodic behavior of the fold and thrust belt in Neuquen, corresponding to compressive phases followed by stages of crustal collapse, at least since the Middle Cretaceous. The study of two main morphostructural units in the arc and retroarc area at 37°-39°S, the Alto de Copahue Pino Hachado, and its continuation to the north in the Chilean Andes (Laguna de la Laja), and the Loncopué trough respectively exemplify this particular behavior. A structural and a stratigraphie study in those areas have given a new evolutionary framework for the Neuquén Andes. © 2005 Asociación Geológica Argentina.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Geomorphologic analysis of the lower and middle section of the drainage basin of the Curri Leuvúriver, Neuquén

The geomorphologic analysis of the study area led to distinguish some formations not considered in previous geological research, as well as to explain the characteristics of the present relief. Thirteen principal geomorphic units produced by different geomorphic processes are recognized. Their variety and incidence through the time are expressed in the glacial morphogenesis concentrated in the western part of the Cordillera del Viento, in the volcanic landscape that predominates in the northern and eastern sectors (calderas, volcanoes, lava flows), in the structural control that defines the morphology of the fluvial process in the central zone and a firstly recognized important landslide to the north of Tricao Malal. As a result of the methodology employed two geological units of different age in the western part of the Tromen-Waile volcanic field were distinguished, which were initially interpreted as a single formation. A limited but consistent structural analysis of the region is also included.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Reconnaissance of prehistoric rock-avalanches and rock blocks slides in the Andean area of Neuquén (37°15′-37°30′S)

Five prehistoric rock-avalanches are described in the northern cordilleran region of Neuquén Province, between 37°15′ and 37°30′S and between 70°55′ and 71°05′W. These slides and their deposits were not previously identified and moreover they were classified as glacial and glaciofluvial in origin. All of them are developed on volcanic-sedimentary deposits. They are named after local places: Cerro Piche Moncol, Cerro Guañaco, Cerro Coronal, Laguna Negra and Laguna Lauquen Mallin avalanches. The first three form a group of avalanches situated north of Reñileuvú creek, in the vicinity of the previously described Moncol rock-avalanche. Their break-away zones are located on the lateral slopes of a pre-existing deep glacial valley. The biggest rock-avalanche is the Cerro Piche Moncol and its deposits are due to the collapse of the southern flank of a volcanic edifice with a small caldera. The Cerro Guañaco, Cerro Coronal and Laguna Negra rock-avalanches began as a slump slide to evolving distally into a flow. The slides of Laguna Lauquen Mallín are big rock-block slides. Some local factors, principally contrasting lithology and physical properties, structural factors and more humid conditions during postglacial times favourable conditions for the loss of slope equilibrium. The authors suggest that these gravitational movements triggered by seismic shock. The age of these rock-avalanches is unknown but they must be younger than last local glaciation. © 2005 Asociación Geológica Argentina.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Los efectos producidos por la aproximación, colisión y subducción de dorsales pacíficas en los Andes Patagónicos

Los Andes Patagónicos Septentrionales son una cordillera formada inicialmente por la subducción de las placas de Phoenix-Farallón y posteriormente por la de Nazca, que muestran rastros de deformación polifásica desde el Jurásico superior hasta el Neógeno, con posterioridad a la ruptura del Gondwana. El objetivo principal del trabajo es agrupar en dos ciclos esta secuencia compleja de eventos deformativos, los cuales sean dependientes de la distribución de edades en la trinchera oceánica durante la subducción. Al sur del paralelo 38° S, la génesis de los Andes Patagónicos Septentrionales está ligada a los efectos producidos por la colisión de dorsales oceánicas. La situación actual permite ilustrar cómo se produce la distribución de la deformación, durante una subducción oblicua, en un sistema con baja partición de la deformación. En los Andes Centrales Australes, al norte de los 38° S, la corteza se imbrica en el retroarco a partir de una distancia crítica de la dorsal oceánica de Chile. Cuando esta distancia es menor, el sistema de corrimientos en el retroarco se detiene, tal como ocurre en los Andes Patagónicos Septentrionales, donde subduce una corteza oceánica relativamente joven. Los cambios en el tiempo de la configuración oceánica a lo largo de la trinchera debido a la subducción, determinan que los modelos de deformación descritos varíen en el tiempo, pudiéndose definir dos modelos extremos: tipo Andes Patagónicos vs. Andes Centrales Australes. Durante los últimos 120 millones de años, en los Andes Patagónicos se han podido documentar, a partir de la interpretación del registro geológico, dos ciclos de apilamiento orogénico cortical con manifestación en sistemas de acortamiento en el retroarco y posterior fosilización del mismo, relacionados con el acercamiento, la colisión y la posterior subducción de una dorsal oceánica orientada oblicuamente con relación al margen occidental de la placa Sudamericana.The Northern Patagonian Andes are an orogenic belt, which were formed by the subduction of the Phoenix-Farallón plates first and the Nazca plate latter and they present a series of deformational phases since the Late Jurassic to the Neogene. The main objective is to group this complex sequence of deformational events in two cycles, which are related to the age distribution of the subducted oceanic plates. South of 38°S, the origin of the Northern Patagonian Andes is linked to the effects produced by oceanic ridge collision. The present picture shows how strain is distributed in the upper plate, in a low strain partitioned setting, during oblique subduction. The continental crust stacks in the retroarc area, as in the present Central Andes to the north, under a certain critical length between the Chilean trench and the oceanic ridge. When this distance reaches that threshold length the thrust systems stop, as in the Northern Patagonian Andes, where very young oceanic crust is being subducted. As the oceanic configuration changed in time along the trench because of ridge subduction, the described strain crustal types also shifted depicting two contrasting styles such as the present Central Andes vs. Patagonian Andes. For the last 120 million years, at least two cycles of crustal thrusting and retroarc orogenic quiescence have been documented, recording the different tectonic settings in the geological record, associated with the approaching, collision and subduction of seismic oceanic ridges, obliquely oriented with respect to the South American border. Keywords: Patagonian Andes. Oceanic Ridges. Strain Partitioning. Andean mountain building. Argentina. Chile

Identification of the area immediately affected by outburst flood of the Laguna Navarrete, Province of Neuquén (36°30′S-71°W)

Considering the high concentration of rock avalanches in the northern part of the Neuquén province of Argentina (36°-38°S and 70°-71°W) and their association with lacustrine basins forming natural dams, their catastrophic collapse seems not to be such a common process as could be expected for these cases. The present work depicts the area immediately affected by the outburst flood corresponding to the Navarrete dam catastrophic collapse (175 × 106 m3), through a sedimentological analysis, generated since the arroyo Colorado was blocked due to a rock avalanche deposit during not well constrained postglacial times. The outburst flood dispersion is initially inferred based on morphological criteria and then determined from a sedimentological analysis of its matrix. Furthermore, the matrix is compared to that of the fluvial terraces, which have been sampled along the arroyo Colorado. This comparison shows that even though differences among them are not so significant through most of the study area, matrix frequency starts to be distinctive from the most distant point of sampling.Fil:Penna, I.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The rock avalanche of Cerro Los Cardos (37° 10′S, 70° 53′ W) in the northern region of the province of Neuquén

A new and important rock avalanche not previously recognized is described, which is located 25 km west of Andacollo town. It shows two scars (northern and southern ones) where the southernmost one is interpreted as the most important, developed in the western flank of a reduced basaltic plain, where at its northern part of Cerro Los Cardos is located. The movement is complex showing several breakaway zones developed into the landslide deposit, considered as secondary scars, all of them, main and secondary ones, have a NW trending. The movement mechanics seems to have started as a planar landslide considering the local almost vertical bedding of the Lileo Formation. However, the concave nature of the breakaway zones allows to infer a rotational movement after the initial stage of sliding. The movement corresponding to the southern breakaway zone was projected as a flux to the south of the Lileo valley, presumably in successive pulses as indicated by the multiple secondary scars. The movement corresponding to the northern break away zone moved to the west and after-wards seems to be controlled by the slope of the valley, moving through to the Palao valley. The western slope of the Palao valley was covered by avalanche deposits corresponding to a run-up. Los Rojos lake is located in a depression presumably generated by the landslide and consequent fracturing of a rock block detached from a Los Cardos's lavic structural plain. Several factors, particularly the structure, favoured the development of the landslide. We propose a seismic trigger for the Los Cardos's avalanche, having into account the regional seismotectonic characteristics (neotectonic front) and the local structure (lineaments, faults). Other landslides, some of them with volume similar to an avalanche deposit, have been included in a regional map. Moreover, modifications to the regional stratigraphy, particularly referred to the volcanic units, are proposed based on morphological criteria. Other geoforms related to other geomorphological processes, fluvial, volcanic and glacial are identified. © 2005 Asociación Geológica Argentina.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

On the formations of the Pampas in the footsteps of Darwin: South of the Salado

In 1833 during his journey across the Buenos Aires Pampas, Charles Darwin made observations that reflected his thoughts on two major landscape units, Pampa interserrana and Pampa deprimida, later identified by other authors. Darwin grouped the Pampean sediments into a single unit, the Pampean Formation, based upon the lithological homogeneity and the large extension of the deposits; the unit was thought to be of estuarine-marine origin and attributed to the Recent Epoch considering the paleontological content (vertebrates and mollusks). At present, the Pampean sedimentary succession, which accumulated approximately during the last 11-12 Ma, is interpreted as a pedosedimentary sequence due to the ubiquity of pedogenetic features throughout the deposits. Four main subcycles of sedimentation are identified related to reactivations of the Pampean landscape. At a regional scale, the outcrop distribution of Pampean sediments of different ages suggests the dominance of more stable conditions since the late Miocene-Pliocene in a vast area of Pampa interserrana, documented by the formation of calcretes. However, sedimentation during the late Pliocene-Pleistocene was active within the domain of the Salado tectonic basin and Sierras de Tandil. The regional disparity shown by the Pampean stratigraphic record reveals the major morphostructural differences of its basement.Fil:Folguera, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The matrix Kadomtsev--Petviashvili equation as a source of integrable nonlinear equations

A new integrable class of Davey--Stewartson type systems of nonlinear partial differential equations (NPDEs) in 2+1 dimensions is derived from the matrix Kadomtsev--Petviashvili equation by means of an asymptotically exact nonlinear reduction method based on Fourier expansion and spatio-temporal rescaling. The integrability by the inverse scattering method is explicitly demonstrated, by applying the reduction technique also to the Lax pair of the starting matrix equation and thereby obtaining the Lax pair for the new class of systems of equations. The characteristics of the reduction method suggest that the new systems are likely to be of applicative relevance. A reduction to a system of two interacting complex fields is briefly described.Comment: arxiv version is already officia

El terremoto del último 7 de septiembre : tiembla, todo tiembla

Fil: Folguera, Andrés. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Laboratorio de Tectónica Andina; Argentina.Fil: Triep, Enrique. Instituto de Sismología Volponi; Argentina.Fil: González Díaz, Emilio M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Ramos, Víctor A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Laboratorio de Tectónica Andina; Argentina.Los terremotos no son un fenómeno del pasado y las placas que conforman los niveles móviles más\nsuperficiales de la Tierra están aún en pleno movimiento. Con respecto a la intensidad de los mismos y\nsus desplazamientos asociados, la actividad actual, en especial la deformación permanente asociada\na estos terremotos, se ha mantenido en el mismo orden de magnitud que en los últimos 10 millones de\naños. La frecuencia con la que ocurren estos movimientos está también dentro del mismo orden,\nsiendo quizás la diferencia más significativa el avance de la tecnología y las comunicaciones de este\nmundo global que nos permiten conocer al instante este tipo de eventos en cualquier parte del planeta,\npareciendo de esta forma un fenómeno más periódico en la actualidad

Gradients from GOCE reveal gravity changes before Pisagua Mw = 8.2 and Iquique Mw = 7.7 large megathrust earthquakes

Considerable improvements in the measurement of the Earth gravity field from GOCE satellite mission have provided global gravity field models with homogeneous coverage, high precision and good spatial resolution. In particular, the vertical gravity gradient (Tzz), in comparison to the classic Bouguer anomaly, defines more accurately superficial mass heterogeneities. Moreover, the correction of these satellitederived data from the effect of Earth topographic masses by means of new techniques taking into account the Earth curvature, improves results in regional analyses. In a recent work we found a correlation between Tzz and slip distribution for the 2010 Maule Mw= 8.8 earthquake. In the present work, we derive the vertical gravity gradient from the last GOCE only model, corrected by the topographic effect and also by the sediments on depocenters of the offshore region at the PerueChile margin, in order to study a spatial relationship between different lobes of the gravity derived signal and the seismic sources of large megathrust earthquakes. In particular, we analyze this relation for the slip models of the 1996 Mw = 7.7 Nazca, 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco events and for the slip models of the 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes from Schurr et al. (2014), including the previously analyzed 2010 Mw = 8.8 Maule event. Then we find a good correlation between vertical gravity gradients and main rupture zones, correlation that becomes even stronger as the event magnitude increases. Besides this, a gravity fall in the gravity gradient was noticed over the area of the main slip patches at least for the two years before 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes. Additionally, we found temporal variations of the gravity field after 2010 Mw = 8.8 Maule event, related to the main patches of the slip distribution, and coseismic deformation. Therefore, we analyzed vertical gravity gradient field variations as an indirect measure of the variable seismic coupling finding a potential relationship between Tzz and the seismic b-value. These relationships exemplify the strong potential of the satellite only derived models as a predictive tool to determine potential seismic energy released in a subduction segment, determining the potential size of a potential rupture zone, and in particular internal slip distribution that allows inferring coseismic displacement field at surface