Piedmont deposits as seismic energy dissipators, Sierras Pampeanas of Argentina

This study shows the neotectonic deformation occurred in the southern piedmont of the Cumbres Calchaquíes, in the Amaicha and Tafí valleys. Neotectonic deformation manifests itself through faults, folds and diversions of drainage channels. The Amaicha valley is bounded to the north by the Tafí del Valle fault and to the south by the Los Cardones fault. The Cumbres Calchaquíes ride over the Sierra de Aconquija through the Los Cardones and Carapunco faults. The Carapunco fault also has a synestral component, responsible for generating an imbricated system of contractional fractures. In the study region many earthquakes of ≥ 3 and ≥ 4 magnitude coincide with regional faults evidencing its neotectonic activity. The seismic energy dissipated through materials with less cohesion that form the fill of the valleys, generating discrete fault scarps and strongly folded conglomerate strata. The foothills deposits of the Cumbres Calchaquíes absorbed most of the seismic energy released during the reactivation of the faults. Tectonic activity is deforming 630 a BP deposits in the Cumbres Calchaquíes piedmont.

Nuevos sitios fosilíferos y evolución paleoambiental del cenozoico tardío del suroeste de Córdoba, Argentina

New fossil remains were found in Neogene and quaternary sedimentary sequences exposed in Alpa Corral and río San Bartolomé localities (Rio Cuarto Department, Córdoba, Argentina). They were assigned to Nopachtus cabrerai (Xenarthra, Cingulata, Glyptodontidae), Notiomastodon platensis (Proboscidea, Gomphotheriidae) and cf. Trigodon gaudryi (Notoungulata, Toxodontidae), and traces of the Scoyenia ichnofacies, as Taenidium barretti, were identified. Based on these findings, we conclude that: 1, the species Nopachtus cabrerai and cf. Trigodon gaudryi are registered for the first time in the Sierras Pampeanas region and support (along with the rest of the known taxa) a clear faunistic similarity to the Pampean region; 2, the beginning of the Neogene sedimentation in the Alpa Corral area (Las Barrancas river and San Bartolome river) would have started during the early Pliocene (Montehermosan Age); 3, the paleoenvironment would have been a fluvial system, with meandering canals interspersed with paleosols developed in floodplains with overflow deposits or abandoned meanders; 4, the paleontological and sedimentary record suggests a well-marked diachronism (from west-southwest to east-northeast) between the beginning of the Neogene sedimentation in the southern sector of San Alberto valley (late Miocene [Huayquerian Age]), the Alpa Corral region (early Pliocene [Monthermosan Age), and Río La Cruz valley (late Pliocene [Chapadmalalan Age]).

The Maz Metasedimentary Series (Western Sierras Pampeanas, Argentina). A relict basin of the Columbia supercontinent?

The Maz Metasedimentary Series is part of the Maz Complex that crops out in the sierras of Maz and Espinal (Western Sierras Pampeanas) and in the Sierra de Umango (Andean Frontal Cordillera), northwestern Argentina. The Maz Complex is found within a thrust stack of Silurian age, which later underwent open folding. The Maz Metasedimentary Series mainly consists of medium-grade garnet–staurolite–kyanite–sillimanite schists and quartzites, with minor amounts of marble and calc-silicate rocks. Transposed metadacite dykes have been recognized along with amphibolites, metagabbros, metadiorites and orthogneisses. Schist, quartzite and metadacite samples were analysed for SHRIMP U–Pb zircon dating. The Maz Metasedimentary Series is polymetamorphic and records probably three metamorphic events during the Grenvillian orogeny, at c. 1235, 1155 and 1035 Ma, and a younger metamorphism at c. 440–420 Ma resulting from reactivation during the Famatinian orogeny. The sedimentary protoliths were deposited between 1.86 and 1.33–1.26 Ga (the age of the Andean-type Grenvillian magmatism recorded in the Maz Complex), and probably before 1.75 Ga. The main source areas correspond to Palaeoproterozoic and, to a lesser magnitude, Meso-Neoarchaean rocks. The probable depositional age and the detrital zircon age pattern suggest that the Maz Metasedimentary Series was laid down in a basin of the Columbia supercontinent, mainly accreted between 2.1 and 1.8 Ga. The sedimentary sources were diverse, and we hypothesize that deposition took place before Columbia broke up. The Rio Apa block, and the Río de la Plata, Amazonia and proto-Kalahari cratons, which have nearby locations in the palaeogeographic reconstructions, were probably the main blocks that supplied sediments to this basin.

Productivity of natural grasslands in different geomorphological units of the Sierras Pampeanas of Argentina

En las zonas semiáridas de Argentina existe una variación de los pastizales naturales asociados a diferentes unidades de paisaje. Los modelos digitales de terreno son herramientas que han permitido el estudio entre las variables físicas del ambiente y la dinámica y patrones de los ecosistemas semiáridos. Por tal motivo el objetivo de nuestro trabajo fue determinar si existen diferencias en la productividad y composición botánica del pastizal natural en las diferentes unidades geomorfológicas identificadas. La cuantificación de la cantidad de biomasa se realizó por el método del doble muestreo y composición botánica mediante el método de asignación de rangos. Para la determinación de las propiedades geomorfológicas se utilizó un modelo digital del terreno en donde se consideró: pendiente, orientación de laderas, altitud, índice de rugosidad del terreno e índice de humedad topográfica. Se encontraron diferencias en cuanto a la productividad y composición botánica del pastizal natural, influenciado de forma directa e indirecta por las características geomorfológicas como la altura, pendiente y rugosidad. La historia de sobrepastoreo a lo largo de décadas en el piedemonte del área de estudio ha contribuido a la degradación del pastizal mediante la pérdida de especies perennes palatables y la instalación de especies anuales y de baja calidad. Es necesario agregar estaciones de muestreo con escalas temporales más amplias teniendo en cuenta la presión de pastoreo

Origin and Evolution of the W mineralization in the Intrusion-related Hydrothermal Deposits of the Cerro Áspero Mining District, Sierras Pampeanas, Argentina

The Cerro Áspero Mining District (CAMD) is located at the Sierras Pampeanas of central Argentina and hosts significant intrusion-related wolframite mineralization. The ore deposits are associated to hydrothermal quartz veins and breccias, hosted by granitoids and metamorphic rocks at the northern contact zone of the Devonian post-orogenic Cerro Áspero Batholith (CAB). The physico-chemical conditions of the different mineralization styles are yet not totally understood, and aiming to deliver a metallogenetic model, the petrography and composition of the main ore and gangue minerals were investigated, and fluid inclusion and stable isotope studies were performed in quartz, muscovite, wolframite, apatite, pyrite, molybdenite, chalcopyrite, and galena. The integrated results revealed that the CAMD ore deposits were generated within the cooling period of the Cerro Áspero Batholith, throughout three late to post-magmatic hydrothermal mineralizing stages. Based on fluid inclusion studies and stable isotope processed data, it was found that the fluids of the first two stages were probably derived from a magmatic source, whereas the third stage solutions would have been originated from meteoric waters. The temperature of the system at the beginning of the hydrothermal phase, was estimated at 384°C; thereafter, the calculated values suggest a decreasing thermal path. Chemical analyses of wolframite showed that the CAMD ore deposit’s evolution was signed by initial formation of ferberite, and subsequently evolved with an increasing H/F ratio that conduced to hübnerite precipitation in the final stage.