Petrography descriptions and U-Pb zircon datasets from the Archean Pavas Block, Precambrian of Uruguay

Relacionado con el artículo: 10.1016/j.jsames.2021.103364This database is a geological and geochronological compila- tion made to study a small Archean/Paleoproterozoic block located in the centre of the Precambrian rock exposition of Uruguay. Petrographic and field outcrops data supporting the samples from which the zircons for textural analysis and U-Pb dating (LA-ICP-MS) come are presented at first with their descriptions. The first table (1) contains the new U- Pb isotopic data. The second table (2) presents a correlation of textures from different zircon samples. The last table (3) contains an inventory of different U-Pb ages found in an- tecedents. All these data are associated with the paper en- titled: “The Archean Pavas Block in Uruguay: extension and tectonic evolution based on LA-ICP-MS U-Pb ages and air- borne geophysics".CSIC: 2015 C-60

Aquifer recharge capacity assessment of an anthropogenically impacted wetland by the DC resistivity geophysical method

Population growth and social and economic development demand increasing volumes of water for public supply, especially in scenarios where surface sources such as rivers may not meet the basic demands for the population. In southeastern Brazil, with emphasis on the Piracicaba region, there is a conflict over water use regarding agricultural and industrial activities, where the sugar-alcohol sector is widely highlighted. The region has thousands of hectares of sugarcane cultivated, which requires intensive use of fertilizers and pesticides, in addition to the need for large volumes of water in the production of sugar and ethanol, where the main effluent produced is represented by vinasse, used as fertilizer complement and soil hydration in sugarcane fields. This work presents the results of a geophysical diagnosis in a closed wetland, located in a sugarcane field region, to evaluate the hydrogeological function of this environment in aquifer recharge and the risks that land use can cause in the quality and availability of surface and underground water resources. The geophysical survey consisted of nine lines of electrical resistivity tomography in Schlumberger arrangement, submitted to 2D processing and inversion followed by interpolation and generation of 3D visualization models. The results indicate a direct connection between water accumulated in the wetland and the aquifer underneath, separated by an aquitard interface about 44 m thickness. The study points out to the high vulnerability to the input of pesticides and vinasse effluent from the surrounding sugarcane fields to the interior of the wetland, given the absence of riparian forest or buffer zone, in addition to the risk of contamination of surface and groundwater. Understanding the local hydrological dynamics should subsidize the sustainable use of the soil providing preservation of water resources, with emphasis on aquifers, a source of increasing importance in the face of the imminent scarcity of surface resources

Hydraulic conductivity and geophysics (ERT) to assess the aquifer recharge capacity of an inland wetland in the Brazilian Savanna

The inland wetlands can perform the storage of water on the surface and the recharge of aquifers. Even a small wetland can work as a local point of water infiltration, influencing and sustaining the hydrodynamics in the hydrology landscape. These zones have complex mechanisms, as they integrate soil chemical and physical char- acteristics, and relate both surface and groundwater systems. The study area is an inland wetland located in the Ecological Station of Itirapina, São Paulo State (Brazil). The present work aims to unveil the relationship between hydrodynamics and pedological architecture through a detailed study that combines hydraulic con- ductivity tests in situ, geophysical method of electrical resistivity (Electrical Resistivity Tomography technique, ERT), and morphological soil descriptions aiming the validation of the ERT and hydraulic conductivity surveys. Two-dimensional (2D) and pseudo-three-dimensional (3D) ERT have been used to investigate the water flow in the subsurface, the pedological architecture that keeps the wetland hydroperiods, and the link between surface water and groundwater that can set a recharge capacity. The results showed areas with distinct surface patterns related to the density of vegetation cover and water infiltration. The lower infiltration areas are characterized by the presence of a perched water table in grassy areas while higher infiltration is associated with exposed topsoil. ERT 2D and pseudo-3D identified these areas as zones with a connection between soil-water and groundwater systems. Hydrodynamics in the flat plateau is associated with the geochemical evolution of soil cover due to the structural complexity acquired by the iron crust dissolution (laterite) which has sustained the relief. Future studies concerning inland wetlands need to be carried out to certify the role of soil-landscape in the water cycle in the Savanna biome

Historia de la geología precámbrica del Uruguay: revisión de las divisiones estructurales, tectoestratigráficas sus límites y nomenclaturas

En este trabajo presentamos una revisión histórica de la evolución del conocimiento geológico en Uruguay, y particularmente, de las divisiones estructurales precámbricas del territorio nacional. Mostramos su relación contextualizada para cada etapa de la evolución de las teorías y técnicas experimentales regionales y globales. Las divisiones del precámbrico uruguayo comenzaron siendo litológicas según el grado de metamorfismo al que se asociaban. En la década de 1970, la caracterización de las unidades de la región siguió un esquema geocronológico en base a ciclos orogénicos y macizos cristalinos en el marco de la Teoría Geosinclinal. Sólo más tarde, en la década de l980, con el establecimiento y refinamiento de la Teoría de la Tectónica de Placas, comenzaron a dividirse las unidades siguiendo el concepto de cratón y posteriormente, en los 90, según el concepto tectónico de terreno. Así, se establecieron nuevas subdivisiones estructurales que son, de Oeste a Este: el Terreno Piedra Alta, el Terreno Nico Pérez y el Cinturón Dom Feliciano o Cinturón Cuchilla Dionisio y las unidades antagónicas: Terreno Cuchilla Dionisio y Terreno Punta del Este. Sin embargo, cada una de estas unidades presenta sus controversias y divergencias, ya sea en su definición, su nomenclatura o sus límites y se encuentra en constante evolución en la actualidad, entorpeciendo a veces la comprensión de la evolución geológica regional y la ubicación de yacimientos energéticos y minerales. En este trabajo buscamos presentar una revisión bibliográfica sólida para el fundamental entendimiento de los esquemas estructurales y dilucidar las controversias y divergencias de los modelos de evolución geológica del Uruguay actual

Formación Polanco: petrografía, estructura y metamorfismo en la región de polanco-manguera azul

La zona de Polanco-Manguera Azul, abarcada dentro de la faja de esquistos del Cinturón Dom Feliciano posee una asociación litológica conformada cominantemente por mármoles calciticos, subordinadamente dolomíticos, e intercalaciones de calcoesquistos, metaconglomerados, cuarcitas, BIF y micaesquistos. Al estudiarse en detalle los mármoles y particularmente los calcoesquistos, se encuentra que los mismos poseen una asociación mineral dada por Cal+Qtz+Ab+Tr+Phl+Ep+Op, coherente con la facies esquisto verde superior (450-500 °C y 200-600 MPa), así como microestructuras coherentes con ese grado. La estructura de la región, con rumbos dominantemente E-O de la superficie principal (S1), junto con las relaciones de esta con los cuerpos graníticos y las trasnscurrencias de la zona, señalan que dicha área se encontraba operando como un dominio de baja deformación durante el BrasilianoThe Polanco-Manguera Azul region, comprised within the schist belt of the Dom Feliciano Belt, has a lithological association mainly composed of calcitic and dolomitic marbles, with intercalations of calc-schists, metaconglomerates, quartzites, BIF and micaschists. Studying in detail the marbles and particularly the calc-schists, it is found that they have a mineral association given by Cal+Qtz+Ab+Tr+Phl+Ep+Op, consistent with the upper green schist facies (450-500 °C and 200-600 MPa), as well as coherent microstructures. The structure of the region, with main EW strikes of S1, together with the relationships with the granitic bodies and the shear zones of the region, indicate that this area was operating as a low strain domain during the Brasiliano orogen