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Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/6341

O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

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Acesso aberto (Open Access)
Acúmulo e exportação de carbono, nitrogênio, fósforo e metais em canais de maré dos manguezais de Marapanim, Costa Norte Brasileira
(Universidade Federal do Pará, 2020-12-18) MATOS, Christiene Rafaela Lucas de; SILVA, José Francisco Berrêdo Reis da; http://lattes.cnpq.br/1338038101910673; https://orcid.org/0000-0002-8590-2462; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
In this study, we assessed the potential of intertidal mudflat sediments along mangrove forest to accumulate and export carbon, nutrients (N and P) and metals (Fe and Mn), in addition to examine the influence of the Amazonian seasonal rainfall patterns on the physicochemical conditions, diagenetic processes and exchange of nutrients and metals along the sediment-water interface (SWI) in intertidal mudflats fringed by pristine mangroves. The study was carried out in the Marapanim River estuarine system (northern Brazil), which is fringed by extensive areas of well-developed mangroves, part of the largest continuous and best preserved mangrove forest in the world, located approximately 200 km from west of the mouth of the Amazon River. The results of this work are presented in two articles. The first deals with the potential of stocks and accumulation of COT, NT and PT in intertidal mudflat sediments, in addition we investigate the potential sources of sedimentary organic matter (OM). The second assesses the influence of seasonal rainfall pattern on physicochemical properties, the diagenetic processes and the diffusive fluxes of nutrients at the SWI in the Marapanim mangrove creeks. During wet season the salinity values decreased as a consequence of the increase in rainfall, with a dilution-mixing zone in the top sediment (<15 cm). In the dilution-mixing zone, Fe (III) and Mn (IV) reduction are the dominant anaerobic respiratory processes in the sediments. The redox zonation of sediments oscillated in response to the rainfall patterns, with the highest concentrations of Fe2+ and Mn2+ in deeper sediment layers during the dry season. Under suboxic conditions, the mudflat sediments act as a source of Fe2+, Mn2+, NH4 +, and PO4 3- to the water column, and these fluxes were driven by rainfall. The results indicated that mangrove-fringed mudflats are quite effective in retaining carbon, nutrients and iron in sediment solid phases than exporting to the coastal waters, while can potentially be a significant contributor to the oceanic Mn cycle. The potential of these mangrove creeks to accumulate these elements is directly related to grain size, sources and susceptibility of OM degradation. In addition, temporal variability in pyrite formation revealed that the solid phase retention mechanisms are also susceptible to seasonal effects, with lower concentrations of chromium-reducible sulfur (CRS, mainly pyrite fraction) during the dry season. Therefore, we show that these seasonal variabilities implied substantial changes of physicochemical properties and the diagenetic processes, affecting the release of metals and nutrients from the SWI and their accumulation in the sediment.
Acesso aberto (Open Access)
Aplicação de resíduos da mineração de bauxita na síntese de geopolímeros
(Universidade Federal do Pará, 2022-04-08) BARRETO, Igor Alexandre Rocha; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
The process of extraction and beneficiation of bauxite deposits in the bauxite province of Paragominas/Rondon do Pará can generate large amounts of waste, mainly in two stages of the process: mining and processing. In the mining stage of the deposits, the “residue” comes from the removal of a thick layer of clay material (known as Belterra Clay). On the other hand, the “residue” from the beneficiation process is generated after the crushing, grinding and washing stages, which give rise to a large amount of clay material dispersed in a large amount of water. For the present study, it selected Belterra clay from the bauxite deposits of Rondon do Pará, a sample of Bauxite Washing Clay from the Hydro company and a sample of kaolin benefited from Imerys Company. The samples and geopolymers were characterized by X-ray Diffraction (XRD), X-ray Fluorescence (FRX), Gravimetric Thermal Analysis (TG), Differential Exploratory Calorimeter (DSC), Optical Emission Spectrometry with Coupled Plasma (ICP-OES) and Laser Particle Analyzer (APL). Geopolymers were synthesized from Belterra clay, microsilica and NaOH according to the Box-Benkhen design. Synthesis of geopolymers from Belterra clay and beneficiated kaolin was also carried out (a comparative study) using KOH and microsilica. Finally, geopolymers were synthesized from Bauxite washing clay with NaOH and microsilica according to the Doehlert design. In the study with only Belterra clay, the highest resistance result was 47.78MPa and the lowest result was 7.05MPa. In the comparative study between Belterra Clay and beneficiated kaolin, the best results of compressive strength were obtained with the beneficiated kaolin. The compressive strength results of the geopolymers synthesized from the Washing Clay ranged from 8.99 to 41.89MPa. These results demonstrate the positive potential of both samples for the synthesis of geopolymers that can be used as possible “Eco-friendly” substitutes for traditional materials, mainly ceramics and cement.
Acesso aberto (Open Access)
Arcabouço estrutural e geocronologia dos granitóides da região de Várzea Alegre: implicações para a evolução crustal da Província Borborema
(Universidade Federal do Pará, 2024-07-25) SOUSA, Luis Kennedy Andrade de; DOMINGOS, Fabio Henrique Garcia; http://lattes.cnpq.br/3975188208099791; https://orcid.org/0000-0002-2447-3465; GALARZA TORO, Marco Antonio; http://lattes.cnpq.br/8979250766799749; https://orcid.org/0000-0002-7271-4737
In the Borborema Province, in northeastern Brazil, several granitic batholiths and plutons are found, which are records of subduction and collision episodes related to the Brasiliano Orogeny. Within this large orogenic system, the emplacement mechanisms of many granites are closely related to the development of deep-seated shear zones, one of which is the Patos Shear Zone, which in its western segment is composed of slices of rocks such as granites, gneisses, metapelites, quartzites, and amphibolites that form an imbricated system. In this context, the present work was carried out with the aim of bringing new geochronological and microstructural data to add to the understanding of the nature of the processes that formed and modified the undifferentiated granitoids in the Várzea Alegre region (CE). The granites are classified as Biotite Monzogranite and Garnet Monzogranite, they present phaneritic and porphyritic textures, in some places, their mineralogical composition is mainly composed of plagioclase, K-feldspar, and quartz, in addition to biotite, muscovite, and garnet. The granitoids are composed of elongated bodies concordant with the host rocks. The deformation imposed on the granitic bodies developed ductile structures with NE-SW orientation and kinematic criteria indicate that the deformation occurred predominantly dextral. Microstructural features, observed mainly in rocks near the edges of the granitic bodies, show that quartz crystals exhibit microstructures such as sutured to lobate contacts, undulating extinction, ribbons, and the chessboard pattern, indicative of recrystallization by grain boundary migration (GBM), compatible with temperatures of 500ºC. Biotite crystals that define the mylonitic foliation characterize a spaced foliation that separates microlite domains formed by aggregates of quartz and plagioclase, with asymmetric lenticular geometry in the granites, similar to the foliation impressed on the gneisses of the Granjeiro Complex. Based on EBSD data, the granites exhibit a grain size distribution with a concentration of crystals <100 μm. From the pole figures, the quartz OPC shows that the dominant system was rhombohedral to prismatic, indicating a medium to high deformation temperature, in a context of progressive non-coaxial deformation. However, from the interpretation of the misorientation angle, it is shown that during the deformation history of the granites, these bodies underwent lower temperature deformation. U-Pb geochronological data on zircon provided crystallization ages of 573 to 576 Ma for this granitic magmatism. The Hf-TDM C model ages of these granitoids ranged from 2.84 to 3.30 Ga and the ƐHf(t) values from -21.9 to -29.6 suggesting a strong incorporation of mesoarchean crustal source. Similar Sm-Nd data in whole rock show that these granitoids have Nd-TDM model ages between 2.14 and 3.33 Ga and ƐNd(t) values between -20.02 and -31.79, suggesting a strong contribution from meso paleoarchean and paleoproterozoic crust (orosirian to riacian) to the formation of the granitic magma that originated the granites in the Várzea Alegre region (CE). These granitic bodies are classified as Itaporanga type and sin-transcurrent, as they have similar ages and structural features to other sin-transcurrent granitic bodies in the Borborema Province. These granites were generated from magmatism associated with the change in the predominant deformation in the Borborema Province, which was the result of the final stages of the Brasiliano Orogeny within the context of simple deformation, with the development of large shear zones.
Acesso aberto (Open Access)
Argamassas históricas de Belém do Pará.
(Universidade Federal do Pará, 2019-09-16) LOUREIRO, Alexandre Máximo Silva; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
The city of Belém, northern Brazil, known as the metropolis of the Amazon, was established on the banks of the Guajará Bay on January 12, 1616, with the denomination of Nossa Senhora de Belém do Grão-Pará, capital of the Grão-Pará province, now the state of Pará. Currently, Belém still has layers of lime mortar on its colonial and imperial buildings, which protect the secular structures and provide evidence of how this material was produced early in its history. Over the years, the deteriorating aspects identified in lime mortars, which damage both aesthetics and functionality, are related to the humidity, saline efflorescence, biological colonization, and/or anthropic actions. Once deteriorated, mortars require maintenance, consolidation, or replacement, which are difficult procedures that can lead to the use of inappropriate materials. Therefore, a good collect and characterization strategies of the original material is necessary for the restoration of historical monuments, because in studies focused on restoration science, the intervention strategy needs to include the use of building materials compatible with the original materials. Thus, the main objective of this doctoral thesis is to determine the characteristics and properties of historical mortars in Belém do Pará from the 18th and 19th centuries, as well as to propose a restoration mortars compatible with the historic mortars, which using industrial waste from Amazon Region. Therefore, this thesis was structured in three independent and complementary thematic articles, which addresses the topic of the historical mortars of Belém do Pará, since their characterization until the proposal of restoration mortars: 1) Investigation of the historical mortar of Belém do Pará, Northern Brazil; 2) How to estimate the binder: aggregate ratio from aerial lime-based historical mortars for restoration? and; 3) The use of industrial waste of the Amazon region in lime-metakaolin restoration mortars: compatibility assessment. Thus, the physical, chemical and mineralogical characteristics were determined, as well as the physical and mechanical properties of the historical material and the restoration material. The results of the historical mortars characterization pointing their main components, their functions and raw materials, besides indicating the analytical techniques used for binder: aggregate ratio quantification, which obtained good accuracy and reliability in your results. Moreover, the results show a wide range of characteristics and properties obtained through restoration mortars, which can serve as a benchmark for other studies or even for practical applications in historic masonry. Therefore, it was possible to identify the restoration mortars most compatible with the historical mortars of Belém do Pará, Northern Brazil.
Acesso aberto (Open Access)
Avaliação da contaminação por metais pesados em sedimentos por atividades de estaleiros na Baia do Guajará e no canal do Rio Maguari
(Universidade Federal do Pará, 2021-12-17) GUIMARÃES, Robledo Hideki Ebata; WALLNER-KERSANACH, Mônica; http://lattes.cnpq.br/7960214506412584; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Antifouling paints applied on ships contain high concentrations of metals in their composition, mainly copper and zinc, with concentrations above 50% and 20%, respectively. Despite being essential elements for living beings, in high concentrations it causes problems in cell growth and reproduction of organisms. In the city of Belém, State of Pará, a significant amount of industrial and domestic effluents is released into the Bay of Guajará, one of which is related to activities in shipyards. Previous studies have shown evidence of metal contamination in the sediments in the edge of Belém estuary, however, no work has highlighted contamination from shipyards. Therefore, the objective of this work is to evaluate sediment contamination by activities in shipyards and abandonment of vessels in the edge of Belém city. The three samples of sediments were collected in 5 shipyards in Belém, two of which were collected in the less rainy period (September 2017 and November 2019) and one in the rainy season in May 2018. The sediment was collected up to 10 cm deep, and samples of paint fragments and fragments of the hulls of abandoned vessels were collected. The in situ pH of the interstitial sediment water was measured. In the laboratory, the sediment samples were placed in an oven at 60°C to dry, disaggregated and then sieved (< 63μm). The samples of paint fragments and the hulls of abandoned boats were washed with deionized water and dried in an oven at 60°C, macerated, mixed with the sprayed white area and reserved. A sample of the commercial paint most commonly used in shipyards was placed on a cellulose nitrate membrane in a hood, after which part of the sample was removed and macerated. An aliquot of the sediment samples from each shipyard was used for particle size analysis, using a laser particle analyzer. The mineralogical composition of the sediment samples was determined by X-ray diffraction, powder method. The clay minerals were determined by X-ray diffraction, following Stokes' Law and according to the methodology proposed by Moore & Reynolds Jr (2002). For the determination of total organic carbon, a TOC - VCPH analyzer with a combustion detector was used. To determine the concentrations of Cu, Zn, Pb, Ni, Cr, Ba, V, Li, Fe and Al contained in sediment, commercial paint, paint fragments and hull fragments of abandoned ships, the samples were subjected to chemical extraction with aqua regia and determined through Optical Emission Spectrometry with Inductively Coupled Plasma (ICP-OES). For statistical treatment of the data, Spearman's correlation was applied to determine the relationship between the parameters, and the Principal Component Analysis test to determine the relationship of metals with shipyards, control station and diffuse anthropogenic source station. The Wilcoxon test was also applied to verify if there were significant differences in the metal concentrations of the sediments collected in front of the shipyard with the sediments collected that were in contact with the abandoned vessel. To assess the level of contamination by metals, the geoaccumulation index proposed by Muller (1969) was applied. The sediment granulometry of the Belem shore presents a higher proportion of sand and silt. The sediments are composed of muscovite, illite, kaolinite, quartz and plagioclase. The clay minerals identified were: smectite, kaolinite, illite and quartz. The pH values of the interstitial water of the sediment samples from Baía do Guajará and Furo do Maguari were around 5.2 – 6.7. The total organic carbon of the sediment was around 0.6% to 2.2%. The commercial paint analyzed presented the following concentrations: Fe (21.2%), Cu (18,497 mg kg-1), Zn (16,589 mg kg-1) and Al (1.59%). The highest concentrations found in the composition of paint fragments and in the fragments of the hulls of abandoned vessels were: Fe (69.2 %), Ba (29,583 mg kg-1), Zn (9,350 mg kg-1), Pb (1,406 mg kg-1), Cu (697 mg kg-1) and Cr (548.7 mg kg-1). This result revealed that abandonment of vessels is the biggest source of contamination in shipyard areas in the city of Belém. According to the Sediment Quality Guidelines for Metals in Freshwater Ecosystems by Buchman (2008), only the average concentration of Cu, with 41.0 mg kg-1, in the sediment reached values above the Threshold Effects Level for the amphipod, Hyallela azteca (28.0 mg kg-1) in the ABSS shipyard. The other shipyards had copper averages ranging between 13.3 – 28.3 mg kg-1. The other metals had mean concentrations always below the Threshold Effects Level value. Spatially, the sediments that were collected in front of the ABSS shipyard for most metals had higher concentrations compared to the sediments that were in contact with the hull of the abandoned ship, of this shipyard. However, the sediments that were collected in front of the MS shipyard in general had lower concentrations compared to the sediments that were in direct contact with the abandoned vessel. Those that presented with concentrations of Cu (39.0 mg kg-1), Zn (120.0 mg kg-1) and Cr (32.0 mg kg-1) that exceed the value of Threshold Effects Level for the amphipod. However, the Wilcoxon Rank statistical test did not attest significant differences in the sediment collected in front of the shipyards with the sediment that was in contact with the abandoned vessels. The main elements that make up the antifouling paints: Cu, Zn had a strong positive correlation (r = 0.80; p<0.05). The Principal Component Analysis confirmed contamination by the metals Cu, Zn, Pb, Ni, Li, Fe and Al and has a stronger relationship with shipyard activities and ship abandonment than with diffuse geogenic or anthropogenic sources The geoaccumulation index classified the sediments close to the IS and ABSS shipyards as moderately polluted for copper with indices of 2.0 and 2.5, respectively. The other metals Zn, Ba, Fe and Al in the studied shipyards show an anthropogenic contribution by activities in shipyards and abandonment of vessels, classifying one or more shipyards as being in a situation close to a polluted environment, for one or more studied metals, with geoaccumulation index close to 2. The results can support additional studies of metal contamination through activities in shipyards and abandonment of vessels, and it can assist in the application of waste management in shipyards and ship cemeteries around the world.
Acesso aberto (Open Access)
Caulim calcinado: estudo cinético da dissolução do alumínio em meio ácido e aplicação como precursor na produção de sílica porosa
(Universidade Federal do Pará, 2016-12-19) LIMA, Paula Elissa Antonio de; NEVES, Roberto de Freitas; http://lattes.cnpq.br/9559386620588673
A kinetic study of metakaolin (calcined kaolin) dissolution was carried out using kaolin for paper coating derived from the Rio Capim region (Pará State, Northern Brazil). The kaolin was calcined at 700ºC for 2 hours, in order to obtain metakaolin, and then leached with sulfuric, hydrochloric and nitric acid at 95ºC, 80ºC and 70ºC ± 3°C. The leachings were performed using excess acid of 5%. Samples were collected every 15 minutes for 3 hours and subjected to aluminum analysis by the EDTA titrimetric method. Final aluminum extraction of 97.42%, 97.99% and 95.9% was obtained with sulfuric, hydrochloric and nitric acid, respectively. Hydrochloric acid was faster than nitric and sulfuric acid, which showed a similar dissolution behavior. Kinetic models of homogeneous (Integral Method, Method of Half-Lives and Method of Initial Rates) and heterogeneous (Shrinking Core Model) reaction were used. The Shrinking Core Model for spherical morphology with a constant size showed better fit. The leaching process is chemically controlled, with leaching reaction of the first order with respect to aluminum from metakaolin, the first order with respect to sulfuric, hydrochloric and nitric acid concentration and activation energies of 87.78 kJ/mol, 90.60 kJ/mol and 91.58 kJ/mol, respectively. Previous research, using excess acid above 50%, are consistent with the data found in this study carried out with only 5% excess acid. The study about the application of calcined kaolin as a precursor in the porous silica production was carried out with the solid obtained in the leaching process with sulfuric acid. The leached material was a microporous solid, with 86.7% of silica, high specific area (297.13m²/g) and humidity adsorption capacity compatible with commercial silica.
Acesso aberto (Open Access)
Dinâmica da paisagem na porção norte da Ilha do Bananal-TO e adjacências ao longo do Quaternário tardio.
(Universidade Federal do Pará, 2019-08-30) MENDES, Laís Aguiar da Silva; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Paleoclimatic and paleoenvironmental studies aim to understand processes of global landscapes evolution, contributing to the reconstitution of the quaternary landscapes and the climatic and environmental changes to which were submitted during this period of the earth's geological history. Some studies in the Amazon, but especially those led in regions more sensitive, such as ecotones and wetlands, show that these areas underwent various paleoecological changes during the Pleistocene and Holocene. The present study was led in the Bananal Island region located in a transition area between the Amazon and Cerrado biomes. The Bananal Island, considered by many authors the largest river island in the world, occupies an area of about 20,000 km2 and is located between the middle course of the Araguaia River and its tributary by the right branch, the Javaés River, in the state of Tocantins. The northern portion of the island stands out for its complex mosaic of geomorphological features (marginal dikes, abandoned meanders, paleochannels and lakes) and contrasting geobotanical features (forests and savannas), such that reflect the intense hydrodynamic activity in this region. Seasonally it is flooded by rainwater and rising water table, so it is considered a seasonal wetland. The aim of this work is to understand the dynamics of this landscape, based on the mineralogical and chemical composition of soils and sediments and the palynological composition study of lacustrine sediments of this region. Therefore, samples of ravines exposed on the banks of Javaés and Araguaia rivers, sandy bars and lake sediments were collected. Soils and sediments were analyzed for their mineralogy by X-ray diffraction and chemistry by ICP-AES and ICPMS. The sediment cores collected in 2 distinct lakes, one located in the interior of the northern portion of Bananal Island (Quatro Veados Lake) and the other located on the surroundings of the Javaés River (Mata Verde Lake) were analyzed for their palynological content and dated by AMS 14C. The results of this research are presented in 3 articles: the first one treaties about the mineralogy and geochemistry of the soils and sediments of Bananal Island, the bars and ravines along the Javaés River. Therefore, it discusses about the diversified nature of the minerals and chemical elements that the strata and horizons of these surface covers are composed, pointing to geological provenance, as well as the geochemical processes involved in the current and past dynamics of this landscape. The second article presents the dynamics of vegetation over the last 2000 years AP in the interior of Bananal Island and discusses its relationship with local climatic and edaphic conditions. The third article, on the other hand, describes the vegetational succession occurred in the last 400 years AP, based on the pollen record of sediments from a lake located on the Bananal Island surrounds, and analyzes the modern pollen spectrum in the region. The results obtained through this work present a highly diversified landscape in terms of its geoforms, sedimentary and pedogenetic coverings and geobotanical aspects resulting from the various moments of its geological history and which even today is dynamic and intriguing. The soils and sediments of this landscape are varied as their textures (sequences of sandy and clay materials) and mineralogical and chemical compositions, where primary minerals and derivatives of varied degrees of chemical weathering coexist in the same profile, showing moments of contrasting climatic conditions. Even, nowadays it is possible to observe in situ environments with variable dynamics (erosive, sedimentary, pedogenetic, etc.), as well as, several geochemical processes, such as those of oxidation of sandy bars and ravines and also the reductive processes of these ferruginized sands (sometimes, mistakenly confused for lateritic profiles), due to contact with organic acids produced by forest cover and hydromorphic conditions such as they are subjected. Regarding vegetation changes throughout the late Holocene, climate control was observed, but especially edaphic, since this area is seasonally flooded, a fact favored by the clayey nature of the soil surface horizons, the rainfall high rates as a prolonged rainy season (on average 6 months) and extensively flat terrain. Thus, factors such as flood duration and hydromorphism conditions stemming are responsible for controlling the installation of forests and/or savannas that characterize the region. So, the regency of a drier climate with the shortening rainy seasons that causes the water table rise, may represent favorable conditions for the development and advancement of the forest. On the other hand, a wetter climate with longer rainy seasons would cause flooding, covering larger areas and the soils would remain saturated for longer periods, a fact that undermines the advancement of the forest and allows the maintenance or even expansion of savannas, especially those dominated by grasses over the region. However, as already mentioned, the climatic conditions in this region control the expansion of forest formations, but they are not the only protagonists in this process, since the presence of wetland due to low and flat topography, clay soils, soil and sediment saturation is an effective impediment to the forest installation. Another factor responsible for replacing for gallery forest by savanna’s tree, for example, is the channel abandonment, a fact that is currently observed in the region, where it is possible to tread inside these old river beds, many of these places already enriched with species such as Curatella americana and Byrsonima sp among others. The Bananal Island, which is geologically inserted in the context of the Bananal Basin and is bathed by one of the largest hydrographic basins in the Brazilian territory (Araguaia-Tocantins), sets up as an extremely important landscape for understanding the wetlands dynamics and also from the savanna-forest ecotone areas during the Quaternary, since, it fits in both situations. The northern part of the island where this research was developed still needs studies. However, in general, this research has contributed to understand the functional dynamics of this landscape in face of the region climate and environmental changes, as well as to increase the knowledge about the transition landscapes between the Amazon forest and savannas, such as the paleoenvironmental knowledge is still restricted.
Acesso aberto (Open Access)
Efeitos das mudanças climáticas nos limites austral e boreal dos manguezais americanos durante o Holoceno e Antropoceno
(Universidade Federal do Pará, 2021-09-08) RODRIGUES, Érika do Socorro Ferreira; KAM, Biu Liu; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
During the Holocene, mangrove distributions were primarily controlled by climate change and sea level fluctuations. In particular, low winter temperatures in the subtropical coastal areas limited these ecosystems to expand beyond 30°N and 28°S in the North and South Hemisphere. Therefore, under the continuous warming trend during the Anthropocene, mangroves are expected to migrate to more temperate regions previously occupied by saltmarshes (e.g., Spartina sp.). The purpose of this Thesis is evaluate the effects of climate changes and SLR fluctuations on the distribution of American mangroves along the Holocene and Anthropocene, based on satellite and drone images, sedimentary facies, diatoms, pollen, geochemistry (LOI, XRF, TOC , TN, TS, C: N, C: S, δ13C and δ15N) as well 210Pb and 14C datings .To achieve the aforementioned objectives, studies were conducted on the tropical coast of southeastern Brazil - south of the Espírito Santo State (20°41'S), the subtropical coastal regions located on the north (26°6'S) and south (28°29’ S) coast of Santa Catarina, and Louisiana littoral (29° 09' N). The results of this research are presented in four scientific papers. The first one (see, chapter II) deals with the effects of global warming on the establishment of mangroves in the Louisiana littoral (29° 09’ N) during the Holocene. The second scientific paper (see, chapter III) shows southward migration of the austral limit mangroves in South America, according to the increase in minimum winter temperatures in the Anthropocene (southern Santa Catarina coast, 28°29' S). The third manuscript (see, chapter IV) assesses the impacts of sea level rise on tropical mangroves in southeastern Brazil (southern Espírito Santo coast, 20°41'S) during the Holocene and Anthropocene, using a multi-proxy approach. The fourth scientific paper (see, chapter V) addresses the establishment of mangroves in the São Francisco do Sul Bay (north Santa Catarina coast , 26° 6'S), in response to global warming in the last 1000 years. The results indicated a marine transgression off the southern coast of Santa Catarina (28°29’ S) and the Louisiana littoral (29°09’ N) during early Holocene. This natural process converted a lake into lagoons colonized by herbs adapted to an estuarine environment. On the Brazilian tropical coast, the middle Holocene high sea-level stand (2-5 m above the current level) was decisive for the establishment of mangroves. This comportment was observed in an estuary located on the south coast of Espírito Santo (20°41'S) where a herbaceous plain was gradually replaced by a lagoon surrounded by mangroves between ~6300 cal yr BP and ~4650 cal yr BP. However, between ~ 4650 cal yr BP and 2700 cal yr BP the lagoon colonized by mangroves on its margins was converted to a tidal flat occupied by herbs, palms and trees/shrubs reflecting the reduction of estuarine influence in the late Holocene, according to with the fall and/or stabilization of the RSL. From the last thousand years there has been a significant decrease in the occurrence of mangrove pollen in the sediments of the tidal flats of southern Espirito Santo (390 cal yr BP (1560 AD) and 77 cal yr BP (1873 AD), probably caused by a RSL fall associated with Little Ice Age (LIA). Paleoclimatic studies have indicated temperature fluctuations during LIA (380 to 50 cal yr BP) and MCA – Medieval Warm Period (950 to 750 cal yr BP) in the late Holocene and consequent change in the Brazil southern vegetation. These climatic events probably influenced the appearance of the mangrove genera succession in the São Francisco do Sul Bay (north Santa Catarina coast, 26°6' S). The effects of the sea level fall and/or stabilization during late Holocene were recorded on the southern coast of Santa Catarina (Laguna, 28° 29 ′ S) through changes in coastal geomorphology. In this same period at the Louisiana coastline (29°09 ′ N), sandy sediments (overwash sediments) were deposited in these estuaries reflecting the gradual migration of these sediments towards land likely a result of storm events. The position of RSL on the southern Brazilian coast (Laguna, 28° 29 ′ S) and north american (Louisiana coast, 29° 09 ′ N) from the middle Holocene were the same presenting suitable physicochemical conditions for mangrove development, as occurred on the coast of Espírito Santo (~6300 cal yr BP) and São Francisco do Sul Bay (~1500 cal yr BP). However, no mangrove pollen grains were recorded in the sediments of the current austral (Laguna, 28° 29 ′ S) and boreal (Louisiana coast, 29° 09 ′ N) limit of American mangroves during the Holocene. During this time interval, there was a significant contribution of organic matter of estuarine source in tidal flats occupied by Spartina sp. Regarding to global warming and RSL rise during Anthropocene an increase mangrove pollen of Espírito Santo sedimentary cores (20° 40' S) reflected mangrove migration to topographically higher sandy plains previously dominated by herbaceous vegetation. Regarding Laguna mangroves (current southern limit of the American mangroves, 28° 29 ′ S), pollen analyzes, 14C and 210Pb datings indicated that the mangroves were established under estuarine influence between ~1957 and 1986 AD, represented by Laguncularia sp. trees. Spatio-temporal analyzes based on satellite and drone images indicated that mangroves have been expanding in recent decades with the introduction of new mangrove genera. In our study area in São Francisco do Sul Bay (north coast of Santa Catarina, 26°6' S), palynological analyzes and 14C dating revealed that mangroves were established around ~ 1500 cal yr BP represented by Laguncularia sp. followed by Avicennia sp. (~500 cal yr BP) and Rhizophora sp. in the last century. This mangrove succession genera were likely caused by a warming trend in South America during the late Holocene and Rhizophora sp. by warming during the Anthropocene. In relation to the mangroves located on the Louisiana littoral, historical records indicated the presence of small shrubs of Avicennia sp. at the beginning of the 20th century. Currently, remote sensing studies coordinated by Cohen (2021) indicate a latitudinal expansion of Avicennia sp. colonizing areas that were previously occupied by Spartina sp. after two decades of warm winters. Therefore, mangroves migrated from the tropics to temperate zones as winter minimum temperatures increased during the Holocene. The Laguna and Louisiana mangroves (currently South and North American mangroves limit) were only established in the early and mid-21st century, respectively. Such dynamics were likely caused by the natural global warming of the Holocene and intensified during the Anthropocene. This process also caused a RSL rise which resulted in the migration of mangrove from lowlands to new higher tidal flats.
Acesso aberto (Open Access)
Elementos terras raras, U, Th e elementos potencialmente tóxicos em agroecossistemas com uso de fertilizantes no nordeste do Pará
(Universidade Federal do Pará, 2020-11-30) BRAZ, Anderson Martins de Souza; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Amazon region is the last agricultural frontier in Brazil and the increasing demand for food and renewable energy sources has intensified the pressure on land use. The Pará state is one of the world's largest producers of oil palm and black pepper, being the mesoregion Northeast Paraense responsible for the annual production of 1,634,476 tons of oil palm, 39,577 tons of black pepper and 286,768 tons of oranges, which represents 97, 50 and 2% of the Brazilian production. The Amazon soils, to express the high agricultural potential, demand high rates of fertilizer application. However, the raw materials used in the production of agricultural inputs are also sources of soil contamination. Thus, studies that facilitate the understanding of the dynamics of rare earth elements (REEs) and other metals / metalloids in the region's soils are relevant. And, based on the premise that anthropic action, mainly through agricultural activities, has caused significant increases in the levels of these elements in soils, the objective was to evaluate (i) the REEs concentrations and other metals in Amazon agroecosystems of orange, oil palm and black pepper, with 26, 10 and 5 years of implantation, respectively; (ii) determine the contamination rates, such as the enrichment and bioaccumulation factors and; (iii) establishing / discussing relationships with soil properties. The results showed: (i) REEs are extremely correlated to soil pH; (ii) the europium (Eu) presented the largest bioaccumulation factor among the REEs; (iii) the activity concentrations of 238U and 232Th in soil with black pepper cultivation were higher than the world average of 238U (35 Bq kg-1) and 232Th (30 Bq kg-1) according established by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR); (iv) moderate enrichment factors (EFs) for Ba, Pb and Zn (2> EF <5) and significant for As and Cu (5> EF <20); (v) the following orders of bioaccumulation: oil palm - Cu> Zn> Hg> Ni> Ba> Co> As> Cr> Cd ≈ Pb; black pepper - Zn> Hg> Cu> Ba> Ni> Co> Pb >> As> Cr> Cd; orange - Hg> Ni> Ba> Zn> Co> Cu> As> Pb >> Cr> Cd. In this context, this is the first study evaluating the absorption of REEs by Amazonian crops of great importance for global markets. A relevant contribution to predict the accumulation of contaminants in soils resulting from anthropic activities, especially in regions of agricultural importance and environmental vulnerability such as the biome Amazon.
Acesso aberto (Open Access)
Estratigrafia e eventos da transição Neoarqueano-Paleoproterozoico da Bacia de Carajás, sudeste do Cráton Amazônico
(Universidade Federal do Pará, 2020-09-18) ARAÚJO, Raphael Neto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Neoarchean-Paleoproterozoic transition is marked by a series of paleoenvironmental, paleoclimatic and tectonic changes that resulted in dramatic events, which imposed to the Earth novel conditions, some of them with irreversible characteristics. On the paleoenvironmental aspect, it is highlighted the rise of oxygen in the hydrosphere-atmosphere system, onset the Great Oxidation Event (GOE) at around ca. 2.45 Ga. The rise of this gas caused consequently the decrease of the greenhouse gases such as CH4, which promoted the emergence of glacial episodes at around ca. 2.45–2.22 Ga, generically termed the Huronian Glacial Event (HGE). Although several studies support the hypothesis that these glacial episodes represent the first global glaciation of the Earth's history (Paleoproterozoic snowball Earth), stratigraphic and geochronological contradictions impose doubt as to its global extension. Strangely, although this set of events is widely recognized in several cratonic areas around the globe, these events are still poorly understood and/or not yet reported in the Amazonian Craton. In this study, the stratigraphic, sedimentological and geochronological investigation of the volcano-sedimentary succession (ca. 5-km-thick) of the Carajás Basin, situated in the southeastern Amazonian Craton, northern Brazil, allowed the recognition and sequencing of some of these events in this basin. Two new units are being formally proposed to this basin: the Serra Sul and Azul formations. Glacial diamictite intervals of the Siderian–Rhyacian (ca. 2.58–2.06 Ga) occur stacked within the Serra Sul Formation, and are the first reported occurrence of glacial deposits of that age in South America. In paleogeographic terms, the occurrence of Paleoproterozoic glacial deposits in this part of the globe, expands the reach of these glaciations to the Amazonian Craton for the first time, although the Serra Sul diamictite may be correlated with any of the know Paleoproterozoic glaciations, or none of them. Well-preserved textures, such as glacial foliation and dropstone features, indicate that the deposition of the Serra Sul Formation occurred in a coastal subglacial setting, in which glaciogenic sediments were resedimented in submarine fan system, and through ice rafting process in distal waters of the marine environment. The Serra Sul glacial system was developed immediately above of pre-glacial strata represented by the Neoarchean banded iron formation and volcanic rock units, which not was the main substrate, but also was the main source of sediments to this glacial system. Additionally, the stratigraphic results indicate that the immediately above of the Serra Sul diamictite, rhythmite deposits of the Azul Formation, locally enriched in manganese, were deposited in a shallow marine environment (offshore and offshore transition/shoreface zones), as a result of the sea level rise during the deglaciation phase. The manganese-bearing strata were possibly deposited in association with black shale deposits—which allowed the formation of rhodochrosite during diagenesis—in deep zones of the marine basin. Petrographic and mineralogical evidences, supported by field observation, indicate that manganese oxides were secondarily remobilized through faults to zones with low strain and high permo-porosity within red bed strata of the Azul Formation, similarly to that observed in hydrocarbon migration. In stratigraphic terms, the Azul Formation represents the same interval previously arranged in the lower member of the Águas Claras Formation. This formation was redefined to designate exclusively sandstone, conglomerate and jasper conglomerate strata, deposited in a braided fluvial system, which occur in unconformably immediately above of the Azul Formation. Moreover, it is suggested that the Azul and Águas Claras formations are the stratigraphic record associated with a transgressive-regressive sequence (T-R). The dating (U-Pb) of detrital zircon grains separated from the Azul and Águas Claras formations indicate that Meso- to Neoarchean rocks, possibly of the Rio Maria and Carajás domains, were the main source of sediments. The 207Pb/206Pb Age distribution of the 76 concordant analysis of the Azul Formation indicate a youngest population at ca. 2.27 Ga, interpreted as the maximum deposition age of this unit. The occurrence of Rhyacian to Siderian zircon grains in this unit strongly suggest that the Bacajá Domain may have been a subordinated source of sediments, and in paleogeographic terms, suggest a possible connection between this domain and the Carajás Domain at that time period. The integration of the results obtained from this study, supported by previous data on the regional geology, allowed the proposition of a tectono-sedimentary evolutive model to the Paleoproterozoic succession of the Carajás Basin. It is envisaged that this basin evolved during the greater part of the Paleoproterozoic in a foreland style, as result of the collision of the Bacajá and the Carajás domains during the Transamazonian orogenetic cycle at ca. 2.2–2.0 Ga. The convergent movement of these blocks caused the gradual uplift of the Carajás protocontinent; the closure of the Azul Sea, and installation of a wide fluvial-alluvial system, in which the Águas Claras and Gorotire formations were deposited. This scenario of profound changes is directly related to the Columbia supercontinent assembly at the end of the Paleoproterozoic, that promoted the continentalization and amalgamation of the ancient landmasses that later formed the proto-Amazonian Craton at the end of Paleoproterozoic.
Acesso aberto (Open Access)
Estudo isotópico do depósito aurífero Volta Grande, domínio Bacajá, sudeste do cráton amazônico
(Universidade Federal do Pará, 2024-03-22) PIMENTEL, Helmut Sousa; VASQUEZ, Marcelo Lacerda; http://lattes.cnpq.br/4703483544858128; https://orcid.org/0000-0003-2729-9404; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The area of the Volta Grande of the Xingu River is crucial for the geological understanding of the Siderian and Riacian periods in the Bacajá Domain, Maroni-Itacaiúnas Province, Amazonian Craton, which hosts significant gold mineralizations. The Bacajá Domain is composed of tectonic associations with NW-SE orientation that contain reworked Archean and Siderian fragments, mainly during the Riacian, with significant crustal growth during the Transamazonian Cycle (2.26 to 2.06 Ga). The objective of this thesis is to investigate the tectonic environment and discuss the crustal evolution in accretionary and continental collision settings. The study relied on field surveys, geological-geophysical mapping, petrography, geochemistry, geochronology, and isotopic geochemistry, employing U-Pb and Lu-Hf methods in zircon via SHRIMP and LA-ICP-MS, U-Pb in titanite via LA-ICP-MS and Sm-Nd on whole rock via TIMS. The geological-geophysical integration reveals the NW-SE trending Bacajá Shear Zone with well-defined edges and foliated terrains of high magnetic susceptibilities, plastically deforming the lithotypes within. Petrographic analyses identified metavolcanosedimentary rocks of the Três Palmeiras sequence, the Intrusive Oca Suite (composed of granodiorite, quartz monzodiorite, quartz monzonite, monzodiorite, and diorite), as well as granodiorite, monzogranite, and sienogranite of the Bacajaí Complex and the Arapari Intrusive Suite. The zoned hydrothermal orogenic gold mineralization occurs at the contact between the Três Palmeiras Group and the Intrusive Oca Suite. The geochemistry of mafic volcanic rocks from the lower Itatá Formation of the Três Palmeiras Group indicates evolved tholeiitic character in a mid-oceanic ridge and juvenile island arc setting, while the volcanic rocks of the upper Bacajá Formation are related to calc-alkaline volcanic arcs in active compressional continental margins. Three groups of granitoids representing different phases of magmatic and tectonic evolution in the Bacajá Domain during the Riacian were distinguished, with ages spanning around 110 M.y.: granitoids from the Intrusive Oca Suite at 2.20-2.17 Ga, syenogranite with biotite from the Bacajaí Complex at 2.17 Ga, and biotite-bearing monzogranite from the Arapari Intrusive Suite at 2.09 Ga. The Intrusive Oca Suite comprises intermediate to acid, calcic to alkali-calcic, ultramafic to medium-mafic, metaluminous to peraluminous rocks formed in a cordilleran granitic setting related to volcanic arcs. The REE of Intrusive Oca Suite granitoids exhibit strong magmatic fractionation, reflected in high (La/Lu)N ratios, enrichment in Rb, Th, and K, and depletion in Ba, Nb, P, and Ti, sourced from mafic rocks with varying K contents. The Bacajaí Complex consists of calcic to alkali-calcic, medium-mafic, and peraluminous quartz monzonite, granite, and granodiorite, sourced from x mafic rocks with low-K and high-K components and some input from metasediments. The rocks of the Arapari Intrusive Suite are medium-mafic, calcium-alkali to alkali-calcic, and metaluminous, sourced from mafic rocks with high-K content. The syn- to late-collisional granitoids (Bacajaí Complex and Arapari Intrusive Suite) are enriched in LILE and LREE, exhibiting negative anomalies in Ni, P, and Ti, and depletion in HFSE, typical of orogenic granites in volcanic arcs. In terms of isotopes, the Três Palmeiras sequence has Nd-TDM values ranging from 2.35 to 2.58 Ga, with εNd(t) varying from -0.41 to +3.20. The Intrusive Oca Suite includes rocks with Nd-TDM between 2.24 and 3.06 Ga and εNd(t) ranging from -5.99 to +2.44. U-Pb zircon crystallization ages for this suite are 2203 ± 23 Ma, with Hf-TDM C values between 2.4 and 2.8 Ga and εHf(2.20Ga) ranging from -0.45 to +5.24 for the Ouro Verde body; 2173 ± 7 Ma with Hf-TDM C ranging between 2.3 and 2.6 Ga, and ɛHf(2.17Ga) between +2.04 and +7.65, added to a U-Pb age of 2171 ± 17 Ma in titanite, for the Central body, and 2171 ± 13 Ma, with Hf-TDM C values between 2.4 and 3.4 Ga and εHf(2.17Ga) ranging from -10.32 to +4.34 for the Buma body, indicating distinct crustal generations between the Mesoarchean and Siderian/Riacian. The Bacajaí Complex has a crystallization age of 2165 ± 10 Ma, Hf-TDM C values between 2.5 and 2.8 Ga, and εHf(2.16Ga) ranging from -0.35 to +3.04, with mantelic sources from the Neoarchean. The Arapari Intrusive Suite has a crystallization age of 2094 ± 13 Ma, Nd-TDM at 2.38 Ga, εNd(2.09Ga) at -1.15, Hf-TDM C values between 2.6 and 2.8 Ga, and εHf(2.09Ga) varying from -2.77 to +1.59, indicating a mixture of mantle and crustal sources generated from the Neoarchean to the Siderian. The geological evolution of the study region is marked by various events. In the Siderian, volcanic-sedimentary sequences with tholeiitic basalts and island arc andesites were followed by the emplacement of diorites to granites around 2.20 to 2.09 Ga and collision, originating continental arcs. The most advanced and late stage of the Transamazonian orogeny in the Volta Grande region is represented by the emplacement of peraluminous granitoids from the Arapari Intrusive Suite, closing the complex geological bevolution of the region. The analyses in this study highlight the proposed similarity based on petrographic, geochronological, and isotopic similarities between the Volta Grande region and the Lourenço and Carecuru domains, located in the state of Amapá, in the northeastern portion of the Maroni-Itacaiúnas Province.
Acesso aberto (Open Access)
Evolução crustal do setor Sul da Província Borborema: Domínio Macururé, sistema Orogênico Sergipano, nordeste do Brasil
(Universidade Federal do Pará, 2023-09-29) PEREIRA, Fábio dos Santos; ROSA, Maria de Lourdes da Silva; http://lattes.cnpq.br/9814085660417748; https://orcid.org/0000-0002-5099-829X; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; https://orcid.org/0000-0003-0854-3053
The Sergipano Orogenic System (SOS), located in the southern Borborema Province, is part of a large Brasiliano/Pan-African orogen structured during the Gondwana supercontinent assembly, which spread out to central Africa up to Cameroon. Six domains compose the SOS, namely Estancia, Vaza Barris, Macurure, Maranco, Poco Redondo, and Caninde. The Macurure Domain stretches 350 km from the Sergipe coast to Macurure City, Bahia state. It consists of a succession of quartzites overlaying by a thick package of phyllites, schists, metarhytmites, and metagraywacke, with intercalations of amphibolite and calc-silicate rocks. The rocks were metamorphosed under greenschist-amphibolite facies and intruded by numerous late Cryogenian-Ediacaran granites and mafic plutons. In this work, new geochemical, U-Pb geochronological (zircon and titanite), and isotopic (whole-rock Rb-Sr, Sm-Nd, and Pb-Pb and in situ zircon Lu-Hf) results from the main units composing the Macurure Domain allowed to refine the local stratigraphy and improve the comprehension about sources and processes involved in the generation of the magmatic rocks. U-Pb isotope analyses on detrital zircon from quartzites yielded two main peaks in the ranges of 1980-1950 Ma and 1000-910 Ma, consistent with the Rhyacian Orogeny (2.2-1.9 Ga) e Cariris Velhos event (1.0-0.9 Ga). Paleoproterozoic dates overlap those observed in the Provincia Borborema basement, represented in the study area by the Jirau do Ponciano Dome and Arapiraca Complex. Negative to slightly positive εHf(t) values between -15.6 and +0.5 and Hf-TDMC model ages from 2.5 to 3.5 Ga characterize this population, suggesting extensive reworking of the Archean crust during the Rhyacian-Orosirian periods. Early Neoproteozoic zircon grains display sub- to superchondritic Hf isotope composition (-12.3 to +7.7) and Hf-TDMC model ages from 2.5 to 1.3 Ga, implying the addition of juvenile material and reworking of preexistent crusts during the Cariris Velhos event. Less abundant Mesoproterozoic (1120-1040 Ma) and late Neoproterozoic (880-740 Ma) zircon populations suggest that the sediment deposition took place before the Brasiliano Orogeny. The groups of magmatic rocks were individualized based on field, petrographic, and geochemical features. (i) The oldest plutonic rocks in the area are diorites and gabbros, with minor cumulate hornblendites. They generally show evidence of solid-state deformation and well-developed tectonic foliation, defined by the plagioclase, hornblende, and biotite orientations. These features point to emplacement in a pre- to early-collisional stage between 643 and 628 Ma. Geochemical data reveal a magnesian nature and affinities with the high-K calc-alkaline and shoshonite magmatic series. REE and multielement spectra exhibit enrichment in light REE and large ion lithophile elements, with deep troughs at Ti-Nb-Ta, typically interpreted as a subduction setting signature. Whole-rock isotope data indicate an evolved signature with subchondritic Nd (εNd(t) = -2.0 a -5.2) e radiogenic Sr (87Sr/86Sr(t) = 0.708-0.710), and Pb (206Pb/204Pb = 18.50-19.18; 207Pb/204Pb = 15.69-15.77; 208Pb/204Pb = 38.54-40.04), indicating derivation from an enriched mantle source. High 87Sr/86Sr(t) and Rb/Sr ratios, together with low Sr/Th and Ba/Rb ratios, suggest that the enrichment episode occurred in response to the introduction of sedimentary components in the mantle via subduction processes, leading to the formation of phlogopite as the main metasomatic phase. Hf-TDMC model ages between 2.47 and 2.09 Ga suggest that the enrichment of the lithospheric mantle beneath the southern Borborema Province occurred during the accretionary events of the Rhyacian Orogeny. Incorporating sediments by the mantle peridotites may have led to increasing Rb/Sr, (U-Th)/Pb coupled with decreasing Sm/Nd and Lu/Hf ratios, which resulted in the time-integrated crustal signature observed in the mafic rocks. (ii) Biotite- and muscovite-bearing leucocratic granodiorites, monzogranites, and syenogranites outcrop as stocks and sheets. They show magmatic foliation marked by the orientation of micas and surmicaceous enclaves, parallel to the schistosity of country rocks, indicating synchronous emplacement to the collisional event between 630 and 624 Ma. Leucogranites are metaluminous to strongly peraluminous, high-K calc-alkaline, and magnesian to ferroan. εNd(t) values and Nd-TDM model ages overlap those of their host5 rocks, suggesting derivation from mostly sedimentary protholiths. (iii) The younger group consists of monzonites, quartz-monzonites, granodiorites, and granites, with crystallization ages from 625 to 603 Ma. They are predominantly isotropic and truncate the regional foliation of the country rocks, indicating a late emplacement relative to the collisional event. The metaluminous and magnesian signatures, with high-K calc-alkaline and shoshonite filiations, resemble the composition of experimental liquids obtained by partial melting of basalt protoliths moderately enriched in incompatible elements. Lu-Hf isotope data provided subchondritic εHf(t) values between -8.3 and 4.0 with Hf-TDMC model ages from 1.77 to 2.03, indicating the reworking of ancient continental crust, possibly related to the Cariris Velhos event. The geochemical and isotopic data of this study, together with those available in the literature allows us to infer that the Neoproterozoic geodynamic evolution of the SOS along the western Gondwana margin can be explained by a lithospheric extension of the Borborema Province basement, followed by basin inversion, and continental collision.
Acesso aberto (Open Access)
A evolução dos manguezais nos litorais Nordeste e Sul brasileiros durante o Holoceno
(Universidade Federal do Pará, 2020-09-30) FREIRE, Neuza Araújo Fontes; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
It is possible that climate changes and sea level fluctuations (allogenic processes) are and will cause major changes in mangrove dynamics. However, other driving forces may be significantly affecting this system. Distinguishing allogenic and autogenic influence on mangroves is a challenging question, because mechanisms related to the natural dynamics of depositional environments (autogenic processes) have strong influences on the establishment and degradation of mangroves. Thus, impacts on mangroves caused by autogenic processes may be erroneously attributed to allogenic mechanisms. Therefore, it is imperative to identify the ‘fingerprint’ of global changes in modern mangrove dynamics. This thesis integrates palynological, geochemical, sedimentological data, 14C dating of sedimentary organic matter, geomorphological and vegetation data in order to evaluate the influence of autogenic and allogeneic processes on Brazilian mangroves during the Holocene. Tropical estuaries from Rio Grande do Norte and southern Bahia, and subtropical estuaries in northern and southern Santa Catarina estates with different climatic, geomorphological and oceanographic characteristics were studied. The Relative Sea-Level (RSL) along the Rio Grande do Norte reached modern level and stabilized at about 7,000 cal yr BP, allowing the mangrove establishment at the edges of the Ceará-Mirim River estuary until the nowadays. However, changes in the spatial distribution of mangroves have occurred since then due to channels dynamics in the region (autogenic processes). Considering the mangroves of the Jucuruçu River in southern Bahia, their horizontal and vertical distribution were controlled by the interactions of the changes in the RSL and fluvial discharge. Therefore, the dynamics of these estuarine mangroves during the Holocene was mainly controlled by changes in sea level and precipitation that affected fluvial discharge. These allogeneic mechanisms were the main drivers of the dynamics of these mangroves. However, during the last 600 years, factors intrinsic to the depositional system gained relevance by controlling the establishment and migration of mangroves by deposition and erosion of muddy tidal flats, abandonment and reactivation of channels (autogenic processes). In the case of Santa Catarina mangroves, the RSL rise up to the middle Holocene was decisive for the establishment of tidal flats appropriate for the expansion of saltmarshes. However, mangroves did not tolerate the Holocene low temperatures in the southern littoral of Santa Catarina. The pollen data indicate the establishment of mangroves with Laguncularia around 1,700 cal yr BP, followed by Avicennia and lastly Rhizophora trees, a cold less tolerant genus, around 650 cal yr BP in São Francisco do Sul, north of Santa Catarina. The mangroves of Laguna, south of Santa Catarina, composed of Laguncularia and Avicennia, were established in the current southern limit of the South American mangroves only in the last decades. No evidence was found for the presence of mangroves in Laguna during the Holocene. The establishment of these mangroves in the region probably started during the Anthropocene, as a consequence of the increase in minimum winter temperatures in southern Brazil. Considering changes in precipitation rates over drainage basins that feed mangrove estuaries, as well as trends in RSL rise and temperatures until the end of the 21st century, tropical estuarine mangroves will likely migrate to higher topographically sectors in the interior of the river valleys, where its extension will depend on the volume of river discharge interacting with the RSL rise. Subtropical mangroves are expected to expand to more temperate zones as minimum winter temperatures increase. This process should cause an increase in the diversity of mangrove species, such as the introduction of the Rhizophora genus in the current southern limit of the mangroves, positioned in Laguna-SC. However, in the case of high rates of RSL rise, the relatively new subtropical mangroves are also expected to migrate to topographically higher sectors of the coast.
Acesso aberto (Open Access)
Evolução supergênica do depósito cuprífero Alvo 118 - Província Mineral de Carajás
(Universidade Federal do Pará, 2022-12-15) SANTOS, Pabllo Henrique Costa dos; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
The Carajás Mineral Province is home to one of the most extensive cupriferous belts in the world, where hypogene mineralizations were partially transformed into gossans, later lateritized and/or truncated during landscape evolution. These covers represent an information source for mineral exploration and, in some cases, can be mined together with parental hypogene mineralizations. The plateaus of the South American Surface host complete and lateritized gossans, while the surrounding denuded areas, typical of the Velhas Surface, exhibit incomplete or immature gossans, with the Alvo 118 deposit as an example. In this orebody, the hypogene mineralization was converted into an immature gossan located at depth, while the host rocks were weathered near the surface, forming a mineralized saprolite. The gossan comprises an oxidation zone, which includes goethite, malachite, pseudomalachite, cuprite, tenorite, native copper, ramsbeckite, chrysocolla, and libethenite, with relics of a secondary sulfide zone, represented by chalcocite. These minerals are distributed in the goethite, malachite, cuprite, and libethenite zones, with their mineral successions reflecting the transition of mineralizing solutions from acidic to slightly alkaline conditions and an increase in oxidation potential. This environment was established from the interaction of acid solutions, derived from chalcopyrite dissolution, with the gangue minerals (calcite and apatite) and the host rocks, granodiorites and, secondarily, chloritites, which acted in buffering the system, favoring the formation of new copper-bearing minerals. The strong correlations of CuO with Ag, Te, Pb, Se, Bi, Au, In, Y, U, and Sn in the hypogene mineralization reflect the inclusions of petzite, altaite, galena, uraninite, cassiterite, and stannite in chalcopyrite. In the gossan, Ag, Te, Pb, Se, and Bi remained associated and were incorporated into neoformed copper minerals. On the other hand, Au, In, Y, U, and Sn exhibit greater affinity with iron oxyhydroxides, as well as Zn, As, Be, Ga, Mo and Ni. The δ65Cu values reinforce that the investigated gossan is immature and was not intensely affected by leaching processes. The main mineral phases identified in the saprolite are kaolinite (predominant), associated with chlorite, smectite, vermiculite, quartz, and iron oxyhydroxides. Iron oxyhydroxides are strongly correlated with Ga, Sc, Sn, V, Mn, Co, and Cr, partly derived from the weathering of parent rocks. Additionally, Mössbauer spectroscopy data point to the important role of ferrihydrite and goethite as copper-bearing phases. There is no evidence of copper incorporation by clay minerals. The δ56Fe values indicate a little contribution of primary mineralization to the Fe content of the saprolite, which is more influenced by chlorite weathering. The association Al2O3, Hf, Zr, Th, TiO2, Ce, La, Ba, and Sr represents the geochemical signature of the host rocks, which influence the chemical composition of the three types of mineralization. On the other hand, the association In, Y, Te, Pb, Bi, and Se comprise the main pathfinder elements of the hypogene mineralization. Detailed knowledge of the supergene mineral and geochemical fractionation makes the Alvo 118 deposit a reference guide for investigating immature gossans and mineralized saprolites in denuded areas of the Carajás Mineral Province or equivalent terrains.
Acesso aberto (Open Access)
Evolução tectono-metamórfica e petrogênese de gnaisses migmatíticos e granitoides mesoarqueanos do Subdomínio Sapucaia (Província Carajás): uma abordagem geocronólogica, isotópica e estrutural
(Universidade Federal do Pará, 2025-05-09) NASCIMENTO, Aline Costa do; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Sapucaia Subdomain, located between the Rio Maria Domain and the Canaã dos Carajás Subdomain, exhibits a Mesoarchean lithostratigraphy that includes greenstone belts, TTG suites, migmatized gneisses, sanukitoids, potassic granites, and "hybrids." This study presents a description of the main migmatitic structures of the basement within this subdomain and proposes the individualization of the Caracol, Colorado, Água Azul and São Carlos orthogneisses, grouping them into the Caracol Gneiss-Migmatitic Complex. Intruding this complex and the Sapucaia greenstone belt sequence, the Água Fria Trondhjemite represents a second generation of sodic magmatism, along with the Mg-rich granodiorites of the Água Limpa Sanukitoid Suite and the Xinguara Potassic Granite. The migmatites exhibit features indicative of in situ and in-source syn-anatectic melting, characterized by stromatic metatexites, net-structured metatexites, schollen, schlieren diatexites, and rare occurrences of patch metatexites. The paleosome is composed of orthogneiss and amphibolite, while the leucosome is quartz-feldspathic and the melanosome is biotite-rich. The unsegregated neosome is represented by a fine-grained granodiorite. Anatexis occurred under upper amphibolite-facies conditions (~650–700°C). The orthogneisses of the Caracol Complex are metagranitoids with high SiO2 and Na2O contents, low MgO, and strong REE fractionation. The sanukitoids of the Água Limpa Suite follow a calc-alkaline trend, enriched in Mg, Ni, Cr, and LILEs. Despite being younger, the Água Fria Trondhjemite exhibits geochemical affinity with the gneisses but with higher K2O content. The Xinguara Granite is calc-alkaline, rich in SiO2 and K2O, with pronounced negative Eu anomalies, indicating a crustal origin. Geochronological data indicate protolith crystallization of the gneisses between 2.95–2.93 Ga, with regional metamorphism between 2.89–2.84 Ga, coeval with the granulites of the Carajás Province. The sanukitoids of the Água Limpa Suite and the Água Fria Trondhjemite date to 2.87 Ga, followed by the Xinguara Granite at 2.86 Ga. Isotopic data from the orthogneisses reveal positive ƐHf(t) and ƐNd(t) values (+0.65 to +3.9), with Hf-TDM C and Nd-TDM model ages between 3.21 to 2.98 Ga, suggesting a juvenile source. The sanukitoids show ƐHf(t) and ƐNd(t) values ranging from –3.31 to +1.76, model ages from 3.28 to 2.91 Ga, δ18O values between 5.0 and 7.6‰, and feldspar Pb compositions with μ > 10, indicating a mantle source contaminated by crustal material. The Água Fria Trondhjemite exhibits ƐHf(t) and ƐNd(t) values ranging from +1.14 to +3.59, with Hf-TDM C model ages of 3.05 to 3.21 Ga. The Xinguara Granite has a Nd-TDM model age of 2.94 to 2.86 Ga, with ƐNd(t) values between +1.32 and +2.55. The temporal proximity between mantle extraction and the crystallization age of these granitoids suggests a rapid crustal growth process in the region. Geochemical data indicate that the melt responsible for the high (La/Yb)N ratio gneiss group derived from the melting of non-enriched metabasalts, previously transformed into garnet-amphibolite. Sources compositionally similar to the average Archean metabasalts from the Sapucaia and Identidade Greenstone Belts could generate such melts, though at different degrees of partial melting (25–30% or 10–15%). The low (La/Yb)N ratio gneiss-forming melt could also be derived from a similar source but without garnet. The sanukitoid melt resulted from 19–20% partial melting of a mantle source enriched by 32% of a TTG-like melt within the garnet stability field. The Água Fria Trondhjemite formed from 5–10% partial melting of metabasalts, whereas the Xinguara Granite resulted from different degrees of melting of sources similar to the older gneisses. Experimental petrology suggests that the sanukitoids crystallized at 1000–970°C in the liquidus stage and 700°C in the solidus stage, with crystallization pressures of 900–600 MPa and emplacement pressures of 200–100 MPa. These rocks exhibit mineralogy indicative of crystallization under oxidizing conditions (NNO +0.3 to +2.5) and high-water content (H₂Omelt > 6–7%). The Mesoarchean evolution of the Sapucaia Subdomain occurred in three main phases: (1) >3.0 Ga, formation of the primitive felsic crust; (2) between 2.95–2.92 Ga, formation of the Caracol Complex gneisses; (3) 2.89–2.84 Ga, crustal thickening during sinistral transpressive tectonic associated with exhumation and metamorphism of the TTG basement. Crustal stabilization allowed for the formation of younger sanukitoid and TTG magmas (Água Fria Trondhjemite). The ascent of these magmas supplied heat for the melting of regional basement metagranitoids, leading to the formation of anatectic granites. During this stage, gneissic foliation was obliterated by deformation and intrusion of younger granitoids. The integration of the data suggests that tectonic processes facilitated the generation of both crustal and mantle-derived magmas at the end of the Mesoarchean in the Sapucaia Subdomain. It can be inferred that crustal growth in the Sapucaia Subdomain was initially controlled by mantle plumes associated with vertical tectonics, similar to observations in the Pilbara and Dharwar cratons. However, unlike the Rio Maria Domain, the dome-like structuring of the gneissic basement in this subdomain was intensely obliterated by the action of sinistral transpressive tectonics (non-coaxial deformation), forming sigmoidal bodies with an E-W orientation.
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Fácies e proveniência de depósitos siliciclásticos cretáceos e neógenos da bacia do Amazonas: implicações para a história evolutiva do proto-amazonas.
(Universidade Federal do Pará, 2015-06-23) MENDES, Anderson Conceição; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Siliciclastic deposits exposed near the channel of the modern Amazon River and overlaid by Neogene units have been attributed to the Cretaceous, formally named as Alter do Chão Formation. Integrated studies based on sedimentology, stratigraphy, trace fossils, petrography of sandstones and heavy minerals, as well as, U-Pb dating of zircon grains allowed reconstitute the depositional paleoenvironment and infer the probable source areas of these Cretaceous deposits in the Amazon Basin. Despite its wide geographical distribution throughout the Amazonas Basin, stratigraphic and sedimentological studies of Alter do Chão Formation were located in areas where there was not allowed a better paleoenvironmental and paleogeographic reconstruction. These deposits record the evolution of a large-scale fluvial system or “Big River”, with meandering pattern in the central-eastern Amazonas Basin, while in the western portion of the basin, predominate an anastomosed configuration with large overbank zones colonized by animals and plants. The recorded of this biologic activity are traces fossil of Taenidium, Planolites, Diplocraterion, Beaconites, Thalassinoides, adhesive meniscate burrows and excavations of insects and vertebrates, as well as, root marks. The fluvial succession consists of kaolinitized and locally silicified conglomerates, sandstones and pelites, grouped in eight architectural elements, Gravel Bar, Sand edforms, Lateral Accretion Bar, Levee, Channels, Crevasse Splay Lobes, Abandoned Channel Fills and Overbank Fines. The expressive terrigenous supply probably came of uplifted areas related to Gurupá Arch, eastern limit of the basin, and zircon grains ages range from 1.8 to 2.9 Ga, indicate the Maroni-Itacaiúnas and Central Amazon provinces as main cratonic sources of sediments. The massive sediment input reflected in the hundreds of meters thick of cretaceous deposits, extense for thousands of kilometres, suggests expressives drainages from the craton, feeding an approximate E-W-oriented "Big River”. Probably, the Late Cretaceous paleogegraphy will be similar to current configuration of the modern Amazon River, but with opposite migration, directioned to the Pacific Ocean. The unconformity between Alter do Chão Formation and Neogene deposits attests long period of subarial exposure in the Amazon Basin during the Paleogene, coincident with the development of lateritic-bauxitic profiles. Paleocurrent measures confirms the flow reversion to the east, in direction of Atlantic, during the Neogene. Additionally, the spectrum of zircon grains ages, ranging from 0.5 to 2.7 Ga, comparable to obtained for Quaternary deposits, indicates cratonic and mainly Andean sources, recording the beginning of the Amazon River. The results obtained here allowed, by first time, to propose a transcontinental drainage model for the Late Cretaceous, as weel as, to record the initial sedimentation of proto-Amazon river during the Neogene.
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Fundamentos para o gerenciamento integrado dos recursos hídricos na microbacia urbana do rio Maguari-Açu com vistas à sustentabilidade hidroambiental
(Universidade Federal do Pará, 2012-08-24) SILVA, Valdinei Mendes da; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
The city of Ananindeua, as part of the Belém Metropolitan Region - BMR, has received the negative impacts resulting from the disorderly occupation of territorial space. The natural conditions of the region have been ignored in this process of urban settlement, which is verified by analyzing the current status of surface and underground water resources, which are being rapidly degraded, because of the lack of interventions, that are primarily that guarantee government control of these impacts or the implementation of actions merely reproduce historical actions without success. The analysis of socioeconomic and hydro-environmental conditions demonstrated the hydro unsustainability of this region, as well as the existence of the various conflicts that refers specifically to water resources. In order to counter this situation, are presented basis for the integrated management of water resources in the urban watershed of the river "Maguari-Acu," which seek to reach this sustainability. Such basis were structured in five (05) actions: 1) Division of BMR in six (6) river basin, 2) Environmental zoning in River Basin of Maguari-Açu, 3) Management of soil sealing and runoff, 4) Strategies of social organization for the management of urban watersheds and 5) management of information from the integrated data base. To support such basis, future scenarios were developed, anchored in the legal framework and the existing technological apparatus, instruments sufficient for integrated actions between the government and society in general, making it possible to undertake the processing needed for the construction or reconstruction of cities from principles of sustainability.
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Geocronologia da capa carbonática e proveniência do intervalo Ediacarano Superior-Cambriano da bacia Araras-Alto Paraguai, sul do cráton Amazônico
(Universidade Federal do Pará, 2022-06-21) CARVALHO, Davi Ferreira de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
The Araras-Alto Paraguai basin, on the Southern Amazonian craton includes Cryogenian-Ediacaran-Cambrian deposits related to the Marinoan glacial (ca. 635 Ma) and post-glacial events (ca. 635-600 Ma) and initial stages of Western Gondwana. The glaciogene diamictites of the Puga Formation are directly overlaid by the Neoproterozoic cap carbonate of the lower Araras Group, evidencing the rapid icehouse-greenhouse transition in the context of the Snowball Earth theory. The Araras Group is unconformably superimposed by the Cambrian siliciclastics of the Raizama Formation, lower Alto Paraguai Group. The succession is bounded by U-Pb maximum depositional ages of < 652 ± 5 Ma (basement - Cuiaba Group) and < 528 ± 9 Ma (upper Alto Paraguai Group). Carbonate Pb-Pb ages of 627 ± 32 Ma and 622 ± 33 and δ13C negative excursions in the cap carbonate are coherent with these time estimates. Correlation of the isotopic data of the Araras-Alto Paraguai basin with δ13C and 87Sr/86Sr global curves indicates an age of ca. 614 Ma for the eroded upper limit of the Araras Group. The presence of skolithos at the base of the Alto Paraguai Group confirms the Cambrian age (<530 Ma), implying a stratigraphic gap of ca. 80 x 106 yr between the groups. The available data are still sparse, allowing only imprecise timing of the geologic events in the succession. New δ13C isotopic data with the typical cap carbonate negative signature, with values oscillating between -7 and -4 ‰ complemented the δ13C curves available for the succession, extending stratigraphic correlations over the inner platform of the Araras Group. The LA-ICP-MS U-Pb dating of calcite crystal fans, interpreted as aragonite pseudomorphs, provided the first diagenetic age of 624 ± 6 Ma of the cap carbonate. Textural relations and heavier isotopic signal in the fans (δ13C = -6.80 a -5.85, δ18O = -7.0 a -5.80) compared to the micrite (δ13C = -7.25 a -5.85, δ18O = -8.9 a -7.5), indicates dissolution-reprecipitation under the influence of oxidizing fluids in the diagenetic environment. Such a change in the composition of the diagenetic fluids may be related to the sea level fall during deposition of the highstand system tract of the cap carbonate sequence. The diagenetic age demonstrates that the depositional and diagenetic processes of the cap limestone, including micrite and pyrite precipitation, inversion of aragonite to calcite, burial neomorphism, chemical compaction and calcite dissolution-reprecipitation within the crystal fans lasted ca. 11 ± 6 x 106 yr. Although a similar spectrum of detrital zircon ages indicates the same cratonic source areas for the studied succession, there is a general higher proportion of ages older than 1.25 Ga for the upper Araras Group compared to the lower Alto Paraguai Group. This result corroborates the erosive hiatus between the groups, indicating a relative increase of sources from the SW-SE (<1.25 Ga, Sunsás belt) in detriment of sources to the N-NW (> 1.25 Ga, other terrains of the Amazonian craton) of the basin during the Ediacaran-Cambrian transition. On the other hand, in the cratonic domain, absence of ages younger than 1.38 Ga and paleocurrents persistently to SE for the lower Alto Paraguai Group suggest intensification of the siliciclastic influxes from the NNW. Integration of the sedimentological, chemostratigraphic, geochronological and tectonic data allowed to propose five evolutionary steps for the Ediacaran-Cambrian succession of the Araras-Alto Paraguai Basin: 1) Ice melting with deposition of the cap dolostone (635-632 Ma); 2) Thermal expansion of the ocean with deposition of the cap limestone and highstand system tract of the cap carbonate sequence (ca. 632-615 Ma); 3) Regression with transference of accommodation space to the East (ca. 615- 600 Ma); 4) Complete exposition of Southern Amazonian craton (600 – 530 Ma); and 5) Sea level rise with implantation of a siliciclastic platform (ca. 530-520 Ma). The obtained geochronological and chemostratigraphic data allowed a better stratigraphic characterization of the Araras-Alto Paraguai sedimentation exposed in the southern Amazonian craton, revealing an important part of the geological evolution of the primordial epicontinental seas related to western Gondwana assembly.
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Geologia e Metalogênese do Depósito Au-Ag (Pb-Zn) do Coringa, Sudeste Província Mineral Tapajós, Pará.
(Universidade Federal do Pará, 2020-09-16) GUIMARÃES, Stella Bijos; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706; https://orcid.org/0000-0003-4598-9249
The Tapajós Mineral Province (TMP) is located in the south-central portion of the Amazonian Craton and is considered one of the main metallogenic provinces of Brazil. A significant part of the province comprises felsic volcanic and volcanoclastic rocks and granites, which formed predominantly in two intervals, 2.02 to 1.95 Ga and 1.91 to 1.87 Ga, belonging to several stratigraphic and lithodemic units. Fieldwork, petrography, and high-resolution airborne geophysics allowed us to produce a new map at the 1:100,000 scale for the southeastern portion of the TMP, where the gold and silver (Cu-Pb-Zn) Coringa deposit is located. We identified two new geological units: (1) the volcanic and pyroclastic rocks of the Vila Riozinho Formation, previously attributed to the Iriri Group, including a facies defined here of this formation, which comprises a group of rocks with the largest magnetic content in the region (Vila Riozinho Formation - magnetic pyroclastic facies), and (2) the Serra Alkali Feldspar Granite, which intruded into the Vila Riozinho Formation (VRF). These units are the host rocks of Coringa deposit. The FVR rocks represent a magmatic arc with high K calcalkaline to shoshonitic affinities. There are similarities in the patterns of LILE and HFSE and the multielementar diagrams with the granitic rocks from Creporizão Intrusive Suite (CIS). The contemporaneousness between these units reinforce a possible petrogenetic correlation and converge to the hypothesis of similar sources, of probable remelting of arc rocks. Isotopic data revealed similar behavior between VRF, SAFG and Maloquinha Intrusive Suite expose similar behavior and present negative εNd values; however, it indicates rocks derived from enriched sources (ancient crustal rocks). Therefore these units had the same source during tectonic setting and crustal evolution of TMP. It is a transcurrent post-collisional stage that followed the collision of the Cuiú-Cuiú Magmatic Arc related to the Orosian volcano-plutonic event (2033-2005 Ma). Based on available geochronological information these units can be associated with a volcano-plutonic event that occurred in the Orosirian period, at about 1.98 Ga. The Au-Ag (Cu-Pb-Zn) Coringa deposit, occurs essentially in veins and veinlets whose match the regional trend (NNW-SSE). The host rocks are volcanic and pyroclastic rocks of the Magnetic Pyroclastic Facies (MPF) from the Vila Riozinho Formation (ignimbrites, tuffs, and breccia), and the Serra Alkali Feldspar Granite, with a predominance of the supracrustal rocks The hydrothermal processes affected all lithotypes associated with mineralization, producing distal alteration (carbonate-chlorite-epidote), intermediate-proximal alteration (sericite-pyrite) and proximal alteration (chlorite-hematite). The mineralized veins are generally composed of quartz + pyrite + chalcopyrite + galena + sphalerite + electrum + chlorite + sericite. Gold grains occur as inclusions or fractures in pyrite. The fluids presents low salinity, rich in H2O and poor in CO2, with evidence of mixing (magmatic-meteoric), and the presence of adularia and Mn-carbonate are outstanding features of this deposit. All characteristic converge to confirm an intermediate- sulfidation epithermal deposit as a genetic model to Coringa deposit.
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Hidrodinâmica, transporte e proveniência sedimentar no baixo rio xingu e sua importância como “Tidal River” amazônico
(Universidade Federal do Pará, 2022-07-14) MEDEIROS FILHO, Lucio Cardoso de; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; ASP NETO, Nils Edvin; http://lattes.cnpq.br/7113886150130994
This research is based on the investigation of the processes (geological and hydrodynamic) that govern the recent evolution of a large tributary of the lower Amazon, the Xingu River. The aim was to investigate its aspects of sedimentary evolution and hydrological flows, from already consolidated data on the filling of its ria and how its patterns of transport and sediment trapping, its seasonal and tidal effects have been established, in addition to understanding the role of the Amazon River as a regulator in the dynamics of its tributary. Hydrodynamic measurements of flow, velocity and water level along with bottom sediment and MPS samples were collected at 3 annual seasons (February, June and November). The results provided support for the investigation of the Xingu-Amazonas interaction and the evolution of the bottom morphology of the lower Xingu. The results suggest a filling of the ria both by the Xingu River, forming a prominent headwater delta, and the Amazon River, where tidal variations transport sediments upstream in the Xingu River. On the other hand, large areas in the central part of the ria indicate muddy sedimentation. Elementar geochemistry allowed us to trace part of the history of sediments and source rocks, together with the analysis of immobile elements (Al, Ti, Zr, Hf, Th) and rare earth elements (REE) because they are poorly fractionated during weathering processes. and they are concentrated in the bottom sediments to the detriment of the dissolved fraction of the rivers. The deposits preserved in the lower Xingu River, despite draining cratonic regions in higher areas, confirm that the bottom material is derived from heterogeneous sources with predominantly intermediate igneous compositions and that they underwent important recycling during fluvial transport. The hydrodynamic modeling allowed to indicate the fluvial discharge as the most relevant forcing for the muddy deposition dynamics in the Xingu estuary. From a numerical model, it was possible to extrapolate the flow and transport dynamics beyond the open boundaries, that is, the central portion of the ria, elucidating the interaction mechanism between river and tidal discharge and the associated sedimentary dynamics. The determination of the amplitudes and phases of the tidal components, whether of purely astronomical origin or resulting from shallow waters, as well as the average level and the hourly discharge proved to be fundamental for the understanding of the governing processes.