Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The Tirúa-Mocha Island area (38.2°-38.4° S) in southern Chile has been affected by two megaearthquakes in only 50 years: the 1960 Mw=9.5 Valdivia earthquake and 2010 Mw=8.8 Maule earthquake. We studied in the field the vertical ground movements occurred during the interseismic period between both earthquakes and the coseismic period of 2010 Maule earthquake and 2011 Mw=7.1 Araucanía earthquake. During the 1960 earthquake, vertical coseismic ground movements are typical of subduction related earthquakes with Mocha Island, located close to the trench, experienced bigger ground uplift (150 cm) than that occurred in Tirúa (-20 cm), place located in the continental margin at the latitude of Mocha Island. Then during the 1960-2010 interseismic period, the 1960 coseismic uplift remained at Mocha Island unlike the normal interseismic subsidence that occurred northward at Arauco Peninsula and Santa María Island. Also Tirúa experienced the biggest interseismic uplift (180 cm) in all the area affected later by 2010 Maule earthquake. Then during the 2010 Mw=8.8 Maule earthquake an anomalous vertical coseismic ground uplift occurred in the study area, opposite to that of 1960 since Mocha Island experienced lower (25 cm) ground uplift than Tirúa (90 cm). Subsequently, during the Araucanía 2011 earthquake a ground uplift in Mocha Island (50 cm) and subsidence at Tirúa (20 cm) occurred. These unexpected vertical ground movements can be explained by the existence of an upper plate splay fault located below the sea bottom between Tirúa and Mocha Island: the Tirúa-Mocha splay fault. Considering the last seismic cycle, the activity of this fault would have started after the 1960 Valdivia earthquake. During 2010 Maule earthquake, the main slip occurred at Tirúa Mocha splay fault. Finally during 2011 Araucanía earthquake, the slip occurred mainly at the updip of Wadati-Benioff plane with probable normal activity of Tirúa-Mocha splay fault. Simple elastic dislocation models considering the Wadati-Benioff plane and the Tirúa-Mocha splay fault activity, can account for all the vertical ground movements observed during 1960 earthquake, the 1960-2010 interseismic period, the 2010 Maule earthquake and the 2011 Araucanía earthquake.

The conventional sedimentological model suggests that the accumulation of organic-rich fine-grained sedimentary rocks (

El avance de las tareas de explotación de mármoles en Malagueño, Sierra Chica de Córdoba, Argentina, ha puesto al descubierto en la Cantera Centro, vetas, vetillas y lentes de pirrotina>pirita≅ calcopirita>>esfalerita. Estos cuerpos mineralizados no superan los 0,3 m de espesor y los 2-3 m de largo continuo y, en conjunto, constituyen corridas intermitentes de hasta un centenar de metros. Los depósitos de sulfuros están asociados espacial y genéticamente a cuerpos de skarn. La secuencia metasedimentaria, que hospeda a los depósitos de skarn, constituida mayoritariamente por gneises, anfibolitas y mármoles, está intruida por diques metagábricos anfibólicos con diferenciaciones dioríticas, diques y plutones metatonalíticos y un metagranito álcali-feldespático; todo el complejo se halla metamorfizado en facies de anfibolita media a alta y fuertemente deformado como resultado del evento regional M2-D2/D3 que afectó al basamento neoproterozoico-cámbrico durante la orogenia Pampeana. A excepción de los gneises, todas las litologías registran evidencias de skarnificación diferencial, preferentemente desarrollada en mármoles, anfibolitas y metagranito, y en menor grado en los diques metagabro-dioríticos y metatonalíticos. Las rocas metasomáticas están representadas por un skarn granatífero (Grs27-48Adr22-34Alm15-27Sps9-21) y piroxénico (Hd40-61Di35-54Jo4,7-6,4), formado a partir del reemplazo de un metagranito; un skarn esencialmente piroxénico (Hd42-63Di32-50Jo3-5) desarrollado a partir de anfibolitas y un skarn formado a partir de un mármol cálcico y constituido principalmente por granate (Adr54-71Grs22-40Alm4-7Sps1-2)±wollastonita. Los diques evidencian pobre reemplazo metasomático y carecen de sulfuros de origen metasomático-hidrotermal. La asociación retrogradante se compone de hastingsita, ferroactinolita, epidoto, clinozoisita, sericita, plagioclasa (An18), chamosita y calcita. Los sulfuros están asociados a la paragénesis de relleno tardía del skarn, depositada según la sucesión temporal: calcita→ clinocloro→ cuarzo→pirita→pirrotina→calcopirita+esfalerita, como vetas y vetillas en el skarn de granate-piroxeno y como lentes de pirrotina maciza en el skarn de piroxeno. Los datos microtermométricos obtenidos a partir de inclusiones fluidas en calcita asociada a los sulfuros, la variación de la relación Fe/Mg en clinocloro y las relaciones de equilibrio de fases en pirrotina, sugieren que la paragénesis de relleno con sulfuros se formó entre 360 y 250 °C; cada rango termométrico guarda correspondencia con la secuencia temporal de precipitación de cada fase mineral, iniciada por descenso térmico a partir de un fluido en ebullición de moderada a alta salinidad (14,5 a 33,5% en peso NaCl eq.). La elevada relación Fe+2/(Fe+2+Fe+3) en granates y clinopiroxenos, los altos contenidos de granates subcálcicos (Alm+Sps), la presencia de sulfuros como cristales hijos y las altas relaciones H2S/SO42- del fluido vinculado a la precipitación de sulfuros, sugieren que el sistema evolucionó dominantemente bajo condiciones reductoras, lo que es también consistente con la presencia de pirrotina en la asociación de minerales sulfurados. La presencia de calcopirita y pirita diseminadas en metagabro-dioritas (Cu ~300 ppm), así como los elevados contenidos de Cu en anfibolitas (900 ppm) permiten interpretar a estas litologías como potenciales fuentes de metales (Cu-Fe-Zn±±Ag). Los valores de δ34SΣfluido-4 a+1,4‰ calculados a partir del δ34S de pirita, pirrotina y calcopirita entre 350 y 150 ºC, indican un origen magmático para el azufre, probablemente derivado de la lixiviación o desulfurización de los sulfuros primarios presentes en los intrusivos metagabro-dioríticos. Los metales y el azufre derivados de estos intrusivos y anfibolitas se habrían redistribuido en el skarn, movilizados por la acción de los fluidos metasomático-hidrotermales. Los skarns se habrían formado por infiltración de fluidos metasomáticos profundos e interacción fluido-roca que afectó las distintas litologías del basamento metamórfico-plutónico del Proterozoico superior-Cámbrico. Los fluidos podrían provenir de intrusivos cámbricos no aflorantes o bien de la migmatización del basamento pampeano, canalizados a lo largo de contactos litológicos y fallas/fracturas. Las evidencias de yacencia, texturales y mineralógicas de la mineralización de sulfuros en Cantera Centro sugieren una edad cámbrica pos-deformacional asociada al orógeno Pampeano.

Triassic rock units of northern Chile (28-29° S) record the transition, both in time and space, between two major orogenies that affected the southwestern margin of South America, the Gondwanian and Andean orogenies. The geodynamic configuration of the margin during this transition is still a matter of debate, particularly whether subduction was interrupted or continued under different parameters in between the orogenies. In order to evaluate these hypotheses by understanding the paleogeographic evolution of the margin, this work synthesizes recent stratigraphical, structural and geochronological data from northern Chile (28-29° S), along with detrital zircon analysis and detritus characterization of the two main siliciclastic Triassic basins present in the area. A detailed study of the evolution of the San Félix and the Canto del Agua basins, their source areas, and exhumation processes of the margin recognizes two stages of intra-arc/forearc basins system development separated by a Carnian unconformity. The first stage (Lopingian-uppermost Middle Triassic) develops an eastern intra-arc basin, which is represented by the volcaniclastic rocks included in the Guanaco Sonso Formation and the roots of the volcanic arc represented by Chollay Plutonic Complex, bounded to the east by a Pennsylvanian-Cisuralian basement block. The forearc basin for this stage is constituted by two graben depocenter, separated by a topographic high, of marine to transitional depositional environment and proximal sediment sources. The eastern graben is filled by conglomerates and turbiditic rocks grouped in Members M1 to M4 of the San Félix Formation, and the western graben, by sedimentary and volcanic rocks of the lower section of the Canto del Agua Formation. The second stage (Norian-Rhaetian) involves an eastern intra-arc basin, represented by the volcanic rocks of the La Totora Formation that seals the exhumed roots of the magmatic arc developed in the previous stage, and a marine to transitional forearc basin to the west, represented by the sedimentary rocks of M5 member of the San Félix Formation and the upper section of the Canto del Agua Formation. These two successions show basal fluvial conglomerates unconformably overlying Anisian prodelta deposits of the first stage, recording a major base level drop of the forearc basin.

Wet-meadows are wetlands of high environmental value and common in the Patagonia, Cordillera de los Andes and Pampean Ranges of Argentina. Particularly, the studies about the functioning and dynamics of wet-meadows are still insufficient and partials in Pampean Ranges. In this paper we analyze the geological-geomorphological factors that influenced the origin, distribution, morphometry and dynamics of wet-meadows in highlands of the southern Comechingones Range (Pampean Ranges of Córdoba, Argentina). A paleoenvironmental reconstruction from sedimentological, palynological, diatomological and chronological records of one of these systems is also proposed. The study area is located at an erosion paleosurface developed previously to the andean orogeny, on an igneous-metamorphic basement rocks. This paleosurface is preserved in the eastern slope of the Comechingones Range and shows different degree of fluvial incision. Most wetmeadows are linked to geomorphological environments with low morphodynamic activity, especially in the granitic rocks and loessic/loessoid deposits preserved in summit plains. The main source of sediments for wet-meadows is the reworking of Quaternary loessic/loessoide sequences. The wetmeadow paleorecords suggests the persistence of wetlands in the Comechingones Range highlands during most of the Holocene, with contractions and expansions in response to environmental variability. The Holocene climate conditions were variable, mainly related to changes in water availability and temperature. A drier period than the current, at least temporarily, took place between ca. 7,000 and 4,700 cal. years BP (6,400 and 4,100 14C years BP). Climatic conditions similar to the current ones were likely established since 4,700 cal. years BP (4,326 14C years BP). During the last centuries, incision and drainage networks integration processes, promote the removal of several wetlands, especially since 1,970s due to precipitation increasing and, subordinately, frequent wildfires.

The Puente del Inca, next to the homonymous village, is a natural bridge located on the Cuevas River, at about 2,700 m above sea level in the Central Andes of the province of Mendoza, Argentina. Declared Provincial Natural Monument in 2005, since the beginning of the 20th century it has registered a continuous weakening, mainly related to erosive processes that cause detachments of part of the material that makes up its structure. The objective of this study is to determine the factors involved in the structural regression and restitution of the natural bridge. To achieve this, visual inspection, characterization of thermal springs, measurement of accretion-erosion rate of travertine deposits, testing of materials and the development of a structural numerical model by the Finite Element Method, were carried out. Results indicate that the deterioration is linked, mainly, with changes in the geobiological system that regulates the travertine deposition and to the heterogeneous structure of the bridge. Changes of the geobiological system are related to the activity of the thermal waters present in the area, whose discontinuity and/or fluctuations in the flow rate are influenced by both natural and anthropogenic factors. The heterogeneity of the structure conditions the stability of the monument due to the presence of a less resistant material in the lower part of the bridge arch. From the numerical simulation, safety factors between 1.5 and 3 were determined for the bridge, thus, we conclude the structure is stable against its own weight, as long as the bridge maintains the current conditions.

The Cenozoic rocks lying in the Province of Tacna (18° S), southern Perú, represent approximately 600 m of stratigraphic thickness. This stacking groups the Sotillo (Paleocene), Moquegua Inferior (Eocene), Moquegua Superior (Oligocene), Huaylillas (Miocene) and Millo formations (Pliocene), and these are the sedimentary fill of the Moquegua Basin. The sediments of the three latter formations are organized into nine sedimentary facies and five architectural elements. Their facies associations suggest the existence of an ancient highly channelized multi-lateral fluvial braided system, with upward increase of pyroclastic and conglomeratic depositions. The heavy mineral spectra make each lithostratigraphic unit unique and distinguishable, being the sediments of the Moquegua Superior Formation rich in garnets, titanites and zircons; while the sediments of the Huaylillas and Millo formations in clinopyroxenes. This mineral arrangement becomes an excellent tool for stratigraphic correlations between outcrops and subsurface stratigraphy (by means of well cores studies) and allow to sketch out a new stratigraphic framework and a complex of rocky blocks bounded by normal faults, often tilted. The sediment mineralogy also suggests that the rocks conforming the Western Cordillera were the main source of sediments for the Moquegua Basin in Tacna. In this context, the detritus of the Moquegua Superior Formation derives mainly from the erosion of the rocks forming the Coastal Basal Complex (Proterozoic), the Ambo Group (Carboniferous) and the Junerata/Chocolate Formation (Early Jurassic). The Huaylillas Formation is a pyroclastic and sedimentary unit which components derived mainly from the Huaylillas volcanism (Miocene) and partly from the denudation of the Toquepala Group (Late Cretaceous). The Huaylillas Formation widely contrasts to the underlying Moquegua Superior Formation due its mineralogy and facies. Finally, the detritus of the Millo Formation derived mostly from the rocks forming the Barroso Formation (Pliocene), and their facies represent a higher contrast in relation to the underlying units due its notorious conglomerate facies.

The Agua del Jagüel Formation crops out in the southernmost part of the Calingasta-Uspallata basin, in central western Argentina. The lower part of the unit is characterized by a glacigenic sequence with diamictites and mudstones with dropstones. In the latter, elements of the Aseptella-Tuberculatella/Rhipidomella-Micraphelia Fauna (AT/RM Fauna), such as the brachiopods Rhipidomella discreta Cisterna, Micraphelia indianae Simanauskas and Cisterna and Orbiculoidea? sp., the gastropods Murchisonia? sp., and Glabrocingulum (Stenozone)? sp., the bivalve Nuculanidae indet., rugose corals, and indeterminate fragments of nautiloids and hyolithids, have been identified. The importance of this fauna mainly resides in its paleoenvironmental and biostratigraphic implications. AT/RM Fauna is characteristic of restricted environments with relatively low concentrations of oxygen and nutrients in the seafloor, which is consistent with the glaciomarine sequences in fjord-type coasts suggested for the Agua del Jagüel Formation. The relatively low diversity of the fauna in this unit compared to that defined in the El Paso Formation, located further north in the basin, might suggest more restricted sectors for benthic colonization, related to the paleovalle’s isolation from oceanic waters. The postglacial mudstones with marine invertebrate faunas of late Serpukhovian-Bashkirian age would have been deposited in relatively restricted (palaeofjord) part of the Uspallata-Calingasta basin as well as in open shelf environments. The marine flooding over drastically different coast configurations and the availability of nutrient and oxygen in the water column would have propitiated the development of faunas with important differences in the taxonomic composition and the paleoecological structure (AT/RM and Levipustula Faunas) occurring at the same time interval. Radiometric data in Agua del Jagüel Formation and paleontological records in the glacial-postglacial sedimentary succession in the basin (marine invertebrate faunas, palynomorphs and plants) are the most important tools to adjust the timing of the postglacial transgression. This information herein presented complements the scheme proposed for the Carboniferous sequences throughout the central western of Gondwana but is not sufficient to assign a more precise age of the fauna studied within the late Serpukhovian-Bashkirian interval.

Glacial cirques comprise a distinctive element of relief in alpine landscapes, and their morphometry, distribution and spatial arrangement are generally linked to morphoclimatic factors. This study provides an analysis of morphometric characteristics, floor altitude, aspect and distribution of 251 first-order and 99 "inner" cirques with regard to environmental agents in a selected alpine-type area of the southwestern Fuegian Andes, in Southern Argentina. Parametric variables were extracted and quantified from satellite images and a Digital Elevation Model, and integrated to a Geographical Information System for their systematization and processing. Significant associations were identified between the different geometric and spatial parameters evaluated. Variability in cirque morphometry along the study area suggests that their evolution was regulated to a large degree by glacial dynamics related to Beagle palaeoglacier activity, and by the W-E topographic gradient of the mountain section. The record indicates that most cirques in the Fuegian Andes have undergone allometric enlargement in the three dimensions (i.e., lesser vertical erosion compared to walls' horizontal expansion), with local variations in size and shape controlled by ice residence time, aspect and altitude, whereas geological structure is supposed to have affected cirque formation along the entire mountain chain. Cirque azimuth potentially responds to the combined influence of climate (solar radiation and westerly winds), structure (pervasive faulting and rock bedding) and topography in their development. In particular, dominance of southeasterly aspects is interpreted as a consequence of a relatively cloud-free atmosphere and aridity during past glacial periods in the region, consistently with published evidence. The absence of aspect-related variation in cirque floor altitude is considered to indicate incidence of extensive glaciations in the area (i.e., mostly ice-sheet conditions, with mountain peaks far above the regional equilibrium line altitude or ELA), as well as formation of younger, lower cirques during successive cold periods of different intensity. Occurrence of "inner" cirques inside larger (preexisting) cirques is thought to reflect a temporary positioning of the ELA just above the floor of the container cirque, permitting short-lived, small cirque-type glaciers to develop along structural bedrock weaknesses.

Lake Caviahue, in Patagonia (Argentina), is a very acid water body (Patagonia, Argentina) due to the influx of volcanic fluids. Over the past 18 years, the lake has been progressively alkalinizing and pH is close to the ferric iron precipitation threshold (pH>3,0). Should iron precipitate, wáter and sediment composition will be altered. To set a baseline, trace metal partitioning (Cu, Cd, Cr, Pb, Zn and Mn) was studied for three sediment cores (0 to 16 cm depth) at three sampling stations using a sequential extraction procedure (SEP) and the acid volatile sulfide/simultaneously extracted metals (AVS/SEM) protocol. The total metals content of the sediments ranged between 0 to 408 μg g-1 of dry sediment, with Pb>Cr>Mn>Cu>Zn>Cd. No Cd was measured above the limit of detection. The sediment was richest in Mn and Cr, two non-toxic metals at the pH / Eh combination of the lake basin. Total Pb was at a moderate contamination level although it is associated with the most recalcitrant fraction and therefore has low mobility. The sediment fractions with higher metal content were the oxidizable and residual, the former commonly associated with labile organic matter and pyrite while the latter are related to recalcitrant organic matter and rock forming minerals. In addition, a high correlation was found between Cr, Pb and Mn,thus these metals may be subject to analogous precipitation processes and possibly to co-variation in the volcano effluents. Furthermore, no metals were detected in the exchangeable/carbonates fraction, which is the most labile of all the sediment fractions. The metal content in (SEM) was likewise below the toxicity thresholds of two international sediment quality guidelines and the ratio AVS/SEM was over one, indicative of non-toxicity. Both results indicate that metal mobility in the acidic sediments of lake Caviahue is very low.