A broad range of processes acted simultaneously during the Quaternary producing relief in the Andes and adjacent foreland, from the Chilean coast, where the Pacific Ocean floor is being subducted beneath South American, to the Brazilian and the Argentinean Atlantic platform area. This picture shows to be complex and responds to a variety of processes. The Geoid exemplifies this spectrum of uplift mechanisms, since it reflects an important change at 35 degrees S along the Andes and the foreland that could be indicating the presence of dynamic forces modeling the topography with varying intensity through the subduction margin. On the other hand, mountains uplifted in the Atlantic margin, along a vast sector of the Brazilian Atlantic coast and inland regions seem to be created at the area where the passive margin has been hyper-extended and consequently mechanically debilitated and the forearc region shifts eastwardly at a similar rate than the westward advancing continent. Therefore the forearc at the Arica latitudes can be considered as relatively stationary and dynamically sustained by a perpendicular-to-the-margin asthenospheric flow that inhibits trench roll back, determining a highly active orogenic setting at the eastern Andes in the Subandean region. To the south, the Pampean flat subduction zone creates particular conditions for deformation and rapid propagation of the orogenic front producing a high-amplitude orogen. In the southern Central and Patagonian Andes, mountain (orogenic) building processes are attenuated, becoming dominant other mechanisms of exhumation such as the i) impact of mantle plumes originated in the 660 km mantle transition, ii) the ice-masse retreat from the Andes after the Pleistocene producing an isostatic rebound, iii) the dynamic topography associated with the opening of an asthenospheric window during the subduction of the Chile ridge and slab tearing processes, iv) the subduction of oceanic swells linked to transform zones and v) the accretion of oceanic materials beneath the forearc region. Additionally and after last geodetic studies, vi) exhumation due to co- and post-seismic lithospheric stretching associated with large earthquakes along the subduction zone, also shows to be a factor associated with regional uplift that needs to be further considered as an additional mechanism from the Chilean coast to the western retroarc area. Finally, this revision constitutes a general picture about the different mechanisms of uplift and active deformation along the Southern Andes, in which orogenic processes become dominant north of 35 degrees S, while south of these latitudes dynamic forces seem to predominate all over the Patagonian platform. (C) 2015 Elsevier Ltd. All rights reserved.

Se presenta un caso en el que se observa que las ondulaciones del geoide de libre disponibilidad en la web constituyen un eficaz indicador del estado isostático de estructuras geológicas significativas. Se estudió la cuenca sedimentaria denominada “Valle de La Rioja”, encontrando para ella una máxima ondulación local (filtrada) de -2 metros con base en el modelo Eigen 03. Buscando mayor definición hemos calculado sobre la cuenca ondulaciones del geoide con: a) el método de Stokes en el plano y b) el método de fuentes equivalentes. Ambos proporcionan una ondulación máxima de -1.8 metros, coincidente en aproximadamente un 90% con la ondulación dada a partir de Eigen 03. Comparando el valor de -1.8 metros obtenido con a) y b) con el valor de ondulación encontrado para un modelo isostático de Airy perfectamente compensado, obtuvimos un residuo negativo de unos -60 centímetros que señala claramente una falta de antirraíz. Este resultado concuerda con el exceso negativo que presentan las anomalías de Bouguer, señalando así un nuevo camino expeditivo para evaluar el balance isostático.

In order to find probable vertical movements, gravimetrical models and gravity changes along Argentina's EW profiles were analyzed. In this work, a general tendency of gravity decrease towards the Andes, reaching approximately −1.5 mGal, was found along the central profile. Two more EW profiles—one in the north and the other in the south of Argentina were also remeasured. A careful investigation was performed on the Caucete or Pie de Palo, 1977, earthquake and a gravity difference of −0.37 mGal was found by comparing the measurements made before and after the seismic event. An assumed level variation of +1.30 m and the vertical gradient of gravity known from observation explain well a consistent relationship between the gravity decrease and the elevation of Pie de Palo's East area after the 1977 earthquake (reverse faulting after focal mechanism study). At the same time, studies performed from 1949 to 1982 in Caucete area or SE Pie de Palo yielded a gravity difference of −0.25 mGal with respect to near stations. The great sedimentary basins of Salado and Colorado show a thick sedimentary development (about 7000 m). Both basins show positive gravity anomalies that increase significantly when the upper crust is normalized. The formation of the basin probably develops when asthenospheric materials arise and provoke stresses in the crust which are then released by plastic flow in the lower part and by faulting in the brittle upper part. Then subsidence is controlled by cooling and sedimentary loading. The present high gravity will tend to decrease in accordance with the present active subsidence and the ulterior loading.

El fenomeno sismico esta estrechamente ligado a cambios de gravedad producto de la deformacion y de cambios de densidad en la corteza. Se ha establecido una red de control geodesico con el proposito de establecer relaciones espacio-temporales en la evolucion del campo gravitatorio producido por actividad tectonica. La red esta compuesta por 65 puntos fijos bien materializados y cubre un area de 3.500 km2 con la ciudad de San Juan en su centro. Diez anos de mediciones periodicas han permitido evaluar las velocidades de variacion de la intensidad del campo gravitatorio; estas se ajustan razonablemente por el modelo estadistico de regresion lineal de las observaciones de la gravedad versus tiempo. Los resultados senalan el levantamiento actual de la Precordillera Oriental, que se refleja en aumentos de gravedad (g) en las estaciones situadas al oeste del fallamiento Villicum-Ullum-Zonda y en la disminucion de g al este de la estructura. identificamos tres segmentos activos: a) la falla de La Laja con fuerte disminucion de g, b) el segmento Maradona-Cerro Bayo, con aumentos de g al oeste de la sierra Chica de Zonda y c) una disminucion de g en la falla de La Rinconada. Los datos muestran actividad tectonica en el sistema de fallas del Tulum que exhibe un gradiente en la direccion del lineamiento Cerro Valdivia-Cerro Barboza-Sierra de Pie de Palo que se incrementa hacia el este. Sus variaciones maximas negativas se observan al este del cerro Barboza. Mapas de anomalias magneticas y gravimetricas senalan patrones en el basamento coincidentes con estas estructuras activas.

In the present work, we propose an elastic isostatic flexural model as the dominant mechanism in the generation of structures of the Bermejo foreland basin.The study area has behaved in a different way from the Neogene, therefore it has been divided into at least two stages. The first one, initiates with the formation of the Andean foreland basin up to the beginning of the lifting of Western Sierras Pampeanas. In this stage, the elastic flexure was the predominant mechanism. The second stage, which motivates our work, comprises from the reactivation of the mega fault of Bermejo-Desaguadero up to now, when initiates the elastic bending mechanism on the discontinuous or broken crust.The flexural responses obtained for a crust with an equivalent elastic thickness (Te) between 5 and 7 km, generates a geometry consistent with the current Bermejo basin. These responses are also consistent with the crustal models previously justified from the Bouguer residual anomaly.

Structural analysis of the Las Salinas Basin and its relationship with eolian sediments accumulation in the Medanos Negros area. Las Salinas sedimentary basin is 100 km long, 50 km wide and has a an average height of 500 m above sea level, with a NNW trend. It is located among the Sierras de La Huerta, Guayaguas, Catanal and Las Quijadas to the west, and Sierras de Chepes, Ulapes and San Luis to the east. As a distinctive feature, the basin is crossed from SW to NE by a significant elevation constituted by eolian sediments which reaches about 60 m above the surface. These sediments cover approximately an area 57 km long and 8 km wide. The reinterpretation of seismic data revealed that the basin main structure is formed by three asymmetric N- NW-trending anticlines with their western flanks bounded by a system of high-angle reverse faults with approximate 900 m throws parallel to the anticline axis and a secondary system of faults. This NE-trending secondary system is also of high an- gle with stratigraphic throws of approximately 500 m. The tectonic compressive regime, still active, has a N-NW orientation. The displacements of the above mentioned fault system controlled the main Mesozoic outcrops of the surrounding sierras. A not so evident effect of the mentioned fault system is the formation of an elongated, curved and segmented structure with a ¨Sshape, which controls the ground deformation as a consequence of the dynamic imposed by the tectonics.

A gravimetric study was carried out in a region of the Central Andean Range between 28∘ and 32∘ south latitudes and from 72∘ and 66∘ west longitudes. The seismological and gravimetrical Moho models were compared in a sector which coincides with the seismological stations of the CHARGE project. The comparison reveals discrepancies between the gravity Moho depths and those obtained from seismological investigations (CHARGE project), the latter giving deeper values than those resulting from the gravimetric inversion. These discrepancies are attenuated when the positive gravimetric effect of the Nazca plate is considered. Nonetheless, a small residuum of about 5 km remains beneath the Cuyania terrane region, to the east of the main Andean chain. This residuum could be gravimetrically justified if the existence of a high density or eclogitized portion of the lower crust is considered. This result differed from the interpretations from Project “CHARGE” which revealed that the entire inferior crust extending from the Precordillera to the occidental “Sierras Pampeanas” could be “eclogitized”. In this same sector, we calculated the effective elastic thickness (Te) of the crust. These results indicated an anomalous value of Te = 30 km below the Cuyania terrane. This is further conclusive evidence of the fact that the Cuyania terrane is allochthonous, for which also geological evidences exist.

Crustal analysis of the San Jorge Basin based on Bouguer anomalies and geoid undulations. To evaluate crustal characteristics such as crust type and isostatic balance of the sedimentary San Jorge Gulf Basin, we analyzed observed Bouguer anomalies and ge- oid undulations calculated from free-air anomalies and equivalent sources, comparing them with the responses of a hydrosta- tic compensated basin model prepared using the topographic mass of the area and the basin sedimentary fill. In both cases we found an excess mass that we explained as a significant crustal anti-root that predicts subsidence in the future. Others al- ternatives as for example the emplacement of dense intracrustal masses, do not modified the conclusions.

In the present contribution is shown that the free, online available geoid undulations are an efficient indicator of the isostatic condition of significant geologic structures. This is the case of the sedimentary basin known as the La Rioja valley, where a filtered maximum local undulation of -2 meters was found by applying the Eigen 03 model. Searching for a higher definition, the geoid undulations of this basin were calculated with: a) the planar Stokes’ method, and b) the equivalent sources method. Both provide a maximum undulation of -1.8 meters, which coincides in approximately 90% with the undulation obtained with the Eigen 03 method. Comparing the values of -1.8 meters obtained from a) and b) with the undulation value found for a perfectly compensated Airy isostatic model, a negative residuum of -60 cm was determined, which clearly indicates the absence of an antiroot. This result agrees with the negative excess shown by the Bouguer anomalies, thus opening an expeditious new way for evaluating the isostatic balance.

Application of the analytical signal techniques to the structures of the Salinas Basin.. The area under study is located between the geographic coordinates of 31°17´ and 32°40´ South latitude; and 66°38´ and 67°48´ West longitude, in the neighborho- od of the locality of Marayes in Las Salinas basin, central western Argentina. In the present work the results of gravimetric data processing from this basin and surrounding region are shown. We had applied analytic signal techniques to the Bouguer anomaly along four profiles oriented perpendicular to the main axis of the basin, which extends from Sierras de Ulapes to the east up to Sierra de Guayaguas to the west, and over one profile nearly parallel to the basin main axis with a north-south trend, located from the northern part of the Mascasin basin to the southern part, near San Pedro structural high. Regional scale results show the location and depth of the main fault system to the east of Sierra de Guayaguas, and to the west of Sierra de Ulapes. At local scale, two faults were identified, that could be associated with the basin edges, and also one probable base fault with north-south dominant direction. The areas of dispersed solutions located on the eastern zone of the area, and represented with elliptic marks on profiles 2, 3 and 4 could be related with a stepped fault system in the buried basement, located to the west of Sierra de Ulapes. This setting is justified based on a positive Bouguer anomaly nucleus located in Ulapes and the surrounding zone.

In the present contribution is shown that the free, online available geoid undulations are an efficient indicator of the isostatic condition of significant geologic structures. This is the case of the sedimentary basin known as the La Rioja valley, where a filtered maximum local undulation of -2 meters was found by applying the Eigen 03 model. Searching for a higher definition, the geoid undulations of this basin were calculated with: a) the planar Stokes’ method, and b) the equivalent sources method. Both provide a maximum undulation of -1.8 meters, which coincides in approximately 90% with the undulation obtained with the Eigen 03 method. Comparing the values of -1.8 meters obtained from a) and b) with the undulation value found for a perfectly compensated Airy isostatic model, a negative residuum of -60 cm was determined, which clearly indicates the absence of an antiroot. This result agrees with the negative excess shown by the Bouguer anomalies, thus opening an expeditious new way for evaluating the isostatic balance.

From a gravimetric study done in the Las Salinas basin, situated in the province of San Juan, Argentina, the geometry of the geologic structures that form this sedimentary trough could be determined. The average depth to the basement was found to be about 5 km, and it increases to the north of the basin. The depth values were obtained by applying spectral analysis and Euler deconvolution to the Bouguer anomaly chart. The alineations of the Euler solutions resulted highly consistent with the seismic interpretations and thereby permitted to confirm the existence of a wrench fault system mainly oriented north-south, which flank the sedimentary trough and cuts it off in the middle part. This information, plus densities obtained from logs of two hydrocarbon exploration wells drilled in the basin, permitted the elaboration of a gravity inversion model with variable density, which justifies the Bouguer residual anomaly. The results show that the basin extends over about 5750 km2. The sedimentary depths, reachs 5 km, is 1.5 km larger than those obtained with seismic. This leads to the assumption that our results show the depth of the crystalline basement, whereas the seismic ones indicate a shallower presence of a technical basement.

In the present contribution is shown that the free, online available geoid undulations are an efficient indicator of the isostatic condition of significant geologic structures. This is the case of the sedimentary basin known as the La Rioja valley, where a filtered maximum local undulation of -2 meters was found by applying the Eigen 03 model. Searching for a higher definition, the geoid undulations of this basin were calculated with: a) the planar Stokes' method, and b) the equivalent sources method. Both provide a maximum undulation of-L 8 meters, which coincides in approximately 90% with the undulation obtained with the Eigen 03 method Comparing the values of -1.8 meters obtained from a) and b) with the undulation value found for a perfectly compensated Airy isostatic model, a negative residuum of -60 cm was determined, which clearly indicates the absence of an antiroot. This result agrees with the negative excess shown by the Bouguer anomalies, thus opening an expeditious new way for evaluating the isostatic balance.

The gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks. A network of areal geodetic control (Red G1) was set up with the purpose of establishing space-time relations in the evolution of the gravity field produced by seismo-tectonic activity. The network is composite for 50 points well materialized in the field, and extends over an about 2700 km2 area centered in the San Juan city of Argentina. These bench marks were linked with precise gravity measurements carried out during the years 2000, 2004, 2007 and 2008. The gravity changes are evaluated taking as fix the gravity value in the Instituto Geofísico Sismológico (UNSJ) station. The relative gravity variation field shows a consistent relation with the seismic activity with magnitudes higher than 3 in the area, which was frequent during these years. The most outstanding results indicate that: A) An alignment of maxima with variations up to +0.100 mGal occurs in the Southwest of the Pie de Palo range, Barboza and Valdivia interior mountains. B) A generalized descent in gravity changes to the east of Sierra Chica de Zonda range (topographic uplift). C) The South of the Sierra Chica de Zonda range shows a marked quiescence in the bench marks situated to the west and high changes (-0.090 mGal) to the East of the range. D) A generalized gravity down (upward zone) in the stations situated north of the San Juan River in the interval 2004-2000. If we assign the gravity variations as caused entirely by topographic changes, the height variations would be in the neighborhood of 20 cm in the last 10 years.

Spectral analysis of magnetic anomalies to calculate Curie-temperature isotherm: A methodology to estimate crustal heat-flow for San Juan and La Rioja provinces, Argentina. A method to estimate the depth extent of magnetic sources was applied to the magnetic anomalies from our terrestrial magnetic data base. The analysed region involving the Precordillera Cuyana and the Sierras Pampeanas of San Juan and La Rioja, including the Famatina System. The top (Z~) and bottom (Zb) boundaries of the magnetized crust were calculated from power-density spectra of the total-field anomalies on 2-D ninety windows with 1 .5°xl .5° size. The depths obtained for the bottom of magnetized crust are assumed to correspond to Curie point depths. The values thus obtained for the Precordillera range between 29 and 40 km, whereas for the Sierras Pampeanas, in the Sierra de Pie de Palo, and other mountain chains along the Bermejo-Desaguadero lineament, such depth ranges between 20 and 35 km. From Curie point depths we have proposed a map of heat flow in the studied region. The patterns of heat flow are distinct on the Precordillera and on the Pampean region. The Precordillera geologic province is characterized by low heat flow and deep Curie depths, whereas the Sierras Pampeanas geologic province is characterized by high heat flow and shallow Curie depths. A significant heat flow extending in Northeast-Southwest direction seems to be directly related to Juan Fernández Ridge trace.