Navegando por Autor "MOURA, Candido Augusto Veloso"

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Acesso aberto (Open Access)
Determinação da composição isotópica de estrôncio em águas naturais: exemplos de sua aplicação em águas subsuperficiais da zona costeira na região Bragantina-PA
(2007) BORDALO, Adriana Oliveira; MOURA, Candido Augusto Veloso; SCHELLER, Thomas
Analytical procedures used for determining the concentrations and isotope composition of strontium in subsurface waters, by mass spectrometry, are described. Sampling was performed in coastal plateaus, salt marsh and mangrove environments in the coastal region of Pará. Coastal plateau waters have δ87Sr between 1.51 and 6.26‰ and Sr concentration bellow 58 ppb. Salt marsh waters show δ87Sr between 0.55 and 0.90‰ and Sr concentration between 93 and 114 ppm, while mangrove waters have δ87Sr around zero and Sr concentration above 15 ppm. Differences in the 87Sr/86Sr ratio in these subsurface waters are detected, as well as seasonal variations in the coastal pleteau waters.
Acesso aberto (Open Access)
Evaluation of two genera of benthic foraminifera for down-core paleotemperature studies in the western south atlantic
(2006) COSTA, Karen Badaraco; TOLEDO, Felipe Antonio de Lima; PIVEL, María Alejandra Gómez; MOURA, Candido Augusto Veloso; CHEMALE JUNIOR, Farid
In this study we have compared the oxygen isotopic composition of two genera of benthic foraminifera (Uvigerinaand Cibicidoides) from core-top samples with modern oxygen isotopic composition of seawater (d18O). Based on a new relationship between d18O and salinity for the mid-latitude western South Atlantic, we estimated the isotopic composition of equilibrium calcite (d18Oeq) using two different equations: (1) O'Neil et al. (1969), modified by McCorkle et al. (1997) and (2) Kim & O'Neil (1997). When using (1), the small difference between d18Oeq and d18O of Uvigerina suggests that this genus precipitates its shell close to equilibrium with ambient seawater. The d18OCibicidoides data are 0.82 ‰ lower than the predicted (equilibrium) oxygen isotopic composition. Conversely, using (2) the Cibicidoides d18O data show excellent agreement with the oxygen isotopic composition predicted from d18O and water temperature while Uvigerina d18O data are 0.69 ‰ higher than predicted oxygen isotope equilibrium values. Based on the evidences presented here and on the results from previous studies we suggest using the genus Cibicidoides and applying Kim & O'Neil's (1997) equation for down-core paleotemperature investigations. In the absence of enough Cibicidoides specimens we suggest using Uvigerina d18O data and applying a correction factor of -0.69 ‰.
Acesso aberto (Open Access)
Evolução geológica das sequências do embasamento do Cinturão Araguaia na região de Paraíso do Tocantins (TO), Brasil
(2013-09) ARCANJO, Silvia Helena de Souza; ABREU, Francisco de Assis Matos de; MOURA, Candido Augusto Veloso
Isotopic studies based on single zircon Pb-evaporation and Sm/Nd (whole rock) methodologies, allowed advances at the lithostratigraphic scene and geologic evolution of basement, in the south segment of Araguaia Belt. The identified geological processes took place from the Achaean (2.6 Ga and TDM ages varying between 2.78 and 3.25 Ga) through Neoproterozoic Era. The Paleoproterozoic ortognaisses, represented by Rio dos Mangues Complex, are placed between 2.05 and 2.08 Ga, and they were formed from a mantellic and youthful source, with a small crustal contribution where TDM ages are 2.35 e 2.21 Ga. At the end of the Paleoproterozoic, a strong crustal shortening happened, and a partial melting of isolated and thickening compartments were facilitated, generating some igneous bodies (1.85 and 1.82 Ga) and Serrote Granite (1.86 Ga), that comes from sources situated between 2.50 and 2.43 Ga. At the end of the Mesoproterozoic, the region was marked by taphrogenetic processes, evidenced by the appearance of alkaline magmatism (1.05 Ga), beyond depositional basins, amongst which the one that received the sediments that had originated the supracrustals of Araguaia Belt. Through the inversion in the geodynamic conditions, in the Neoproterozoic, a process of horizontal shortening with crustal thickening and distinct volumetric and spatial melting occurred, which may have generated Matança and Santa Luzia Granites. The Araguaia Belt was built from this tectonic motion. The tectonic mass transport in the Amazonian Craton might have occurred, resulting in the current architecture in the form of imbricate fans.
Acesso aberto (Open Access)
Geologia, geocronologia e litoquímica dos granitos paleoproterozóicos do tipo A no setor setentrional da Província Tocantins
(2008-06) CHAVES, César Lisboa; GORAYEB, Paulo Sérgio de Sousa; MOURA, Candido Augusto Veloso
This work presents the geologic characterization of the Ipueiras Intrusive Suite, which comprises four granitic plutons, named do Carmo, Areias, Ipueiras and Itália, located in Goiás Massif, northern sector of the Tocantins Province. New petrographic, litogeochemical, geocronological and isotopic data had allowed to discriminate these plutons of other granites of the region. Lithochemical data showed that they are peraluminous subalkaline granites, with A-type affinity. Single zircon Pb-evaporation data indicate an age of 2,08 Ga for this magmatism. Sm-Nd (TDM) ages between 2,15 and 2,19 Ga, and positive εNd(2,08 Ga) values (+2,5 to +2,9) for the Areias and Ipueiras granites suggest an origin involving juvenile mantle components. This granitogenesis may be related to the last magmatic pulses of the Transamazonian thermotectonic event, well defined in the region.
Acesso aberto (Open Access)
Geoquímica das águas do médio e baixo rio Madeira e seus principais tributários - Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2013-12) HORBE, Adriana Maria Coimbra; QUEIROZ, Maria Mireide Andrade; MOURA, Candido Augusto Veloso; GALARZA TORO, Marco Antônio
The aim of this paper was study the water of the Madeira River and its tributaries, between the city of Humaitá and its confluence in the Amazon River. There were analyzed: pH, conductivity, turbidity, major ions, trace elements and strontium isotopes during the dry and wet seasons and also, in the transition from the wet to the dry season, throughout 2009 and 2010. The white waters from the Madeira River are bicarbonated, calcic, with pH between 5 and 6 and the ions concentrations are higher than those of the tributaries. The waters of the tributaries are black, are more acidic and are chemically heterogeneous; those from the left margin are chemically similar to the waters of Madeira River, while those from the right margin are enriched in dissolved SiO2. The concentrations of cations, Cl- and NO3- are higher during the wet season due to the contribution of soils, vegetation and the rainwater composition (Cl-), while HCO3-, SO42-, Al, Br e P are concentrated in the dry season, and their higher contents may be related to the bedrock. The higher concentrations of SiO2 and rare earth elements in both dry and wet season are related to vegetation, soil and rocks. The interaction of these factors causes the chemical heterogeneity of the water. However, the chemical similarities between the water tributaries of the left margin and the water of the Madeira River, are probably, consequence of the Andean rocks be the sources of the Cenozoic sedimentary rocks percolated by these tributaries while the chemistry water of the tributaries of the right margin are in accordance with the tectonic stability, the intense weathering and the low erosion rate of the Amazon craton.
Acesso aberto (Open Access)
Granitóides proterozóicos como marcadores da evolução geotectônica da região nordeste do Pará, Brasil
(2009-12) PALHETA, Edney Smith de Moraes; ABREU, Francisco de Assis Matos de; MOURA, Candido Augusto Veloso
Granitoids cropping out inside Phanerozoic sedimentary cover in northeast Pará, Brazil (Gurupi region), records the geotectonic evolution of this region. 207Pb/206Pb single zircon evaporation ages were obtained for different granitoid bodies of the region, besides Sm-Nd isotopic studies. Almost all the plutons are genetically related with regional geological processes operative during this crustal segment formation, which includes the São Luís Craton. Such processes are associated with amalgamation of island arcs and Archean nuclei during the Palaeoproterozoic (2.15 to 2,07 Ga). The reworking of the southwestern margin of the São Luís Craton at the end of the Neoproterozoic formed the Gurupi Belt and is recorded by the occurrence of a granitic pluton of 549 ± 4 Ma.
Acesso aberto (Open Access)
Hidroquímica do rio Solimões na região entre Manacapuru e Alvarães: Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2009) QUEIROZ, Maria Mireide Andrade; HORBE, Adriana Maria Coimbra; SEYLER, Patrick Thierry; MOURA, Candido Augusto Veloso
The present study evaluated the physical and chemical characteristics of the water of the rivers Solimões, Purus and their tributaries, collected in November of 2004 in the State of Amazonas between the cities of Manacapuru and Alvarães and Anamã and Pirarauara. Physical-chemical analyses (temperature, pH, electrical conductivity, turbidity, Ca2+, Na+, K+, Mg2+, HCO3-, SO42-, Cl-), and trace-elements (Li, B, Al, Sc, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Rb, Sr, Mo, Cd, Sb, Cs, Ba, Pb, La, Ce e U) and Sr isotopes were accomplished. The analyzed parameters and the chemical composition show that the waters of the rivers and tributaries of the central region of the Amazonia are chemically distinct between them. The white waters of Solimões are calcium-bicarbonate and of Purus are bicarbonates, and the respectives tributaries are sodium-potassium-bicarbonate and sodium-potassium-sulphate. This causes the white poorly acided waters to the neutrals and more conductives, while the black ones are less mineralized, more acids, mainly of Purus. The Ba, Sr, Cu, V e As in highest levels differentiate the Solimões white waters of the Purus`s waters, well as the tributaries of the first related to the second. This complex of caracteristics indicates that the Solimões as the Purus and their respectives tributaries are submitted to geological/ambiental distinct conditions. The influence of arrives in port of sediments of Andes is diluted at the currency of basin of the Solimões and it reflects on formation of fertile valleys Solimões and Purus. By another view, the crust rocks, represented by the Shields of the Guianas and Brasileiro both contribute, but in a reduced proportion.
Acesso aberto (Open Access)
Mineralogia e química dos sedimentos de fundo do médio e baixo Madeira e de seus principais tributários: Amazonas - Brasil
(Instituto Nacional de Pesquisas da Amazônia, 2011) QUEIROZ, Maria Mireide Andrade; HORBE, Adriana Maria Coimbra; MOURA, Candido Augusto Veloso
This study reports the granulometric, mineralogic and chemical analyses, including Pb isotope, carried out on the bottom sediments of the Madeira River, whose headwaters are in the Andes Mountain, and its tributaries that come from the cratonic region, in order to investigate the compositional variation of the sediments transported by the major rivers of the Amazon. The analytical data show that the bottom sediments of the Madeira River have higher amounts of sand and quartz, and lower contents of Al2O3, Fe2O3, K2O, MgO, Na2O, PF, TiO2O, P2O5, MnO and trace elements, and the maturity increases toward downstream. Among the tributaries, the bottom sediments from Machado and, secondarily, Marmelos rivers are those that more closely match the composition of the sediments of Madeira River. The sediments of Jamari River, with higher proportion of Ti2O, Zr, Y, Nb, Ga, Hf, U, Ta and REE, are quite distinct. In spite of the intense weathering and erosion, in humid tropical conditions, that the rocks drained by the Madeira river basin have been submitted, the Th/Co, Th/Pb, Th/Yb, Al/Pb, Zr/Co ratios and Pb isotope data indicate that different sources contributed to the bottom sediments. It is suggested that mafic rocks are the main source of the sediments of the Madeira River, while felsic rocks are the source of the tributaries.
Acesso aberto (Open Access)
Petrogenesis, U-Pb and Sm-Nd geochronology of the Furna Azul Migmatite: partial melting evidence during the San Ignácio Orogeny, Paraguá Terrane, SW Amazon Craton
(Universidade Federal do Pará, 2016-06) NASCIMENTO, Newton Diego Couto do; RUIZ, Amarildo Salina; PIEROSAN, Ronaldo; LIMA, Gabrielle Aparecida de; MATOS, João Batista; LAFON, Jean Michel; MOURA, Candido Augusto Veloso
The Furna Azul Migmatite is a ~10 km2 complex located in Pontes e Lacerda city, Mato Grosso, Brazil. It belongs to Paraguá Terrane, limit with Rio Alegre Terrane, southeast of San Ignacio Province, in Amazon Craton. It consists of transitional metatexites with amphibolite enclaves and dioritic injections. The rocks were divided in residuum rich and leucosome rich; both have three deformation phases marked by folded stromatic layers affected by spaced foliation and metamorphosed in amphibolite facies, represented by garnet, biotite, sillimanite, and by the clinopyroxene in the enclaves. The metamorphic retrograde to greenschist is marked by formation of chlorite, muscovite and prehnite. Residuum-rich metatexites show higher CaO and Na2O contents, separating them from K2O, Ba and Rb enriched transitional metatexites. U-Pb on zircon and Sm-Nd whole-rocks dating indicates that the residuum-rich metatexite crystallized at 1436 ± 11 Ma, with a TDM age of 1.90 Ga and εNd(1.43) of -0.54, whereas the dioritic injection crystallized at 1341,7 ± 17 Ma with a TDM age of 1.47 Ga and εNd(1.34) of 3.39. These results indicate that the Furna Azul Migmatite protolith was formed during the San Ignácio Orogeny and was reworked during the same orogeny, as basement for collisional to post-magmatic granites from Pensamiento Intrusive Suite.
Acesso aberto (Open Access)
Petrografia, geocronologia e significado tectônico do Nefelina Sienito Brejinho: extremo noroeste da Província Borborema
(2011-09) GORAYEB, Paulo Sérgio de Sousa; BARBOSA, Rita de Cássia de Oliveira; MOURA, Candido Augusto Veloso; LEMOS, Ronaldo Lima
In the extreme northwest of the Borborema Province was identified an alkaline massif named Brejinho Nepheline Syenite, emplaced in Paleoproterozoic gneisses of the Granja Complex. The investigation involved the mapping, detailed petrographic analyses and Rb-Sr geochronology, allowing to the reconstruction of the evolutionary history of this pluton in the tectonic context of the Borborema Province. Five petrographic facies have been mapped and the mineralogical and textural/structural analyses performance suggest the processes of fractional crystallization, with strong control of gravitational action and liquid immiscibility in the history of magmatic crystallization of the massif. The age of 554 ± 11 Ma was obtained by Rb-Sr wholerock geochronology and was interpreted as the minimum age for crystallization and emplacement of Brejinho Nepheline Syenite in the late Neoproterozoic. The tectonic context of the alkaline magmatism may be related to the extensional event responsible for the formation of Jaibaras Graben in western Ceará, as well as the emplacement of a number of granitic plutons whose ages range from 530 to 590 Ma. Similar situation was identified in the north of the Paleozoic Amazon Basin involved the Maicuru Alkaline-Ultramafic-Carbonatite Complex (589 Ma) emplaced in the Paleoproterozoic gneissic basement of the Amazoniam Craton. The geological framework places the Brejinho Nepheline Syenite after the strike-slip tectonics represented by Santa Rosa Shear Zone (Transbrasiliano Lineament), and before the formation of the Parnaíba Basin. Therefore, this alkaline magmatism may be interpreted as an important record of the rift phase that heralded the installation of the basin in the early Paleozoic. The identification of this alkaline massif, so far without any similar occurrence in the Borborema Province, opens new perspectives for research in basement of Parnaiba Basin, considering the tectonic and metallogenic importance that represents this type of magmatism.
Acesso aberto (Open Access)
Proveniência das rochas metassedimentares do Cinturão Araguaia com base em datações Pb-Pb em zircão e idades-modelo Sm-Nd
(2011-06) PINHEIRO, Bruno Luís Silva; MOURA, Candido Augusto Veloso; GORAYEB, Paulo Sérgio de Sousa
This paper presents single zircon Pb-evaporation ages, obtained in detrital zircon grains, and Sm-Nd (TDM) for metassedimentary rocks of the Araguaia belt, to investigate the possible source areas of these rocks, and to contribute to understanding the geologic evolution of this belt in the context of the West Gondwana amalgamation. Quartzite of the Morro do Campo Formation, located in the north segment of the belt (Xambioá region) gave Archean 207Pb/206Pb zircon ages (2.65-3.0 Ga), while in the south segment (Paraíso do Tocantins region), the 207Pb/206Pb zircon ages were mainly Meso-Neoproterozoic (1.25-0.85 Ga), and, secondarily, Paleoproterozoic (1.85-1.70 Ga). These results suggest the existence of different sources areas for this quartzite. The Sm-Nd (TDM) model ages of metapelites (slate, phyllite and micaschist) present bimodal distribution with the main population occurring between 2.1 and 1.4 Ga (mode in 1.6-1.7 Ga), and a less abundant population between 2.7 and 2.4 Ga. These data have been interpreted as mixing of Paleoproterozoic (or even Archean) sources with younger, probably Meso-Neoproterozoic, sources. The main candidates to be the sources of the metassedimentary rocks of the Araguaia belt would be those crustal segments located in the southeastern (São Francisco Craton, Goiás Massif, Goiás Magmatic Arc). The sedimentary succession deposited in the Araguaia oceanic basin and the associated magmatic rocks were transported, later, towards the east margin of the Amazonian Craton, during the main tectonic that led to the structural development of the Araguaia belt as a result of the West Gondwana amalgamation.
Acesso aberto (Open Access)
Síntese geológica e geocronológica do Cráton São Luís e do Cinturão Gurupi na região do Rio Gurupi (NE-Pará / NW-Maranhão)
(2013-08) KLEIN, Evandro Luiz; MOURA, Candido Augusto Veloso
The Gurupi region in northern Brazil has been divided into Paleoproterozoic (São Luís Craton) and Neoproterozoic (Gurupi Belt) geochronological domains based on Rb-Sr and K-Ar. Recent zircon (Pb evaporation) dating of most of the lithostratigraphic and lithodemic units, in addition to limited whole-rock Sm-Nd determinations, shows virtually all rock units (juvenile or reworked) formed between ~2.0 Ga and 2.2 Ga. A single granitoid shows a Neoproterozoic crystallization age (~0,55 Ga), and the Archean has been recorded only in inherited zircons and in protolith Sm-Nd model ages. The compositional, metamorphic, structural, geophysical and geochronological characteristics of the geological units supports the previous subdivision into two domains. However, they also reveal a common Paleoproterozoic evolution of both the Gurupi and São Luís domains. The Gurupi domain is characterized as a collisional orogen, whereas the São Luís domain shows accretionary characteristics, with both participating in the widespread Paleoproterozoic collage at 2.2 - 2.0 Ga. During the Neoproterozoic, the southern border of this region was affected by strong strike-slip shearing and very limited lithogenesis, reflecting the Brasiliano orogenic collage elsewhere and defining the presently observed relationship between the São Luís Craton and the Gurupi Belt.
Acesso aberto (Open Access)
Strontium isotope stratigraphy of the Pelotas Basin
(2014-03) ZERFASS, Geise de Santana dos Anjos; CHEMALE JUNIOR, Farid; MOURA, Candido Augusto Veloso; COSTA, Karen Badaraco; KAWASHITA, Koji
Strontium isotope data were obtained from foraminifera shells of the Pelotas Basin Tertiary deposits to facilitate the refinement of the chronostratigraphic framework of this section. This represents the first approach to the acquisition of numerical ages for these strata. Strontium isotope stratigraphy allowed the identification of eight depositional hiatuses in the Eocene-Pliocene section, here classified as disconformities and a condensed section. The reconnaissance of depositional gaps based on confident age assignments represents an important advance considering the remarkably low chronostratigraphic resolution in the Cenozoic section of the Pelotas Basin. The recognition of hiatuses that match hiatuses is based on biostratigraphic data, as well as on global events. Furthermore, a substantial increase in the sedimentation rate of the upper Miocene section was identified. Paleotemperature and productivity trends were identified based on oxygen and carbon isotope data from the Oligocene-Miocene section, which are coherent with worldwide events, indicating the environmental conditions during sedimentation.
Acesso aberto (Open Access)
Tratamento estatístico de dados geoquímicos e sua aplicação ao mapeamento geológico e definição de anomalias geoquímicas no alvo 2 - corpo 4 - Província Mineral de Carajás
(Universidade Federal do Pará, 1982-12-29) MOURA, Candido Augusto Veloso; RAMOS, José Francisco da Fonseca; http://lattes.cnpq.br/8189651755374537
A geochemical soil survey was .carried out in the Alvo 2 - Corpo 4 area of t.he Província Mineral de Carajás (Carajas Mineral Province), Pará, Brazil. Sample elements were collected and analyzed in order to determine, for each one of them, the degree of concentration of the following chemical elements: iron, aluminum, magnesium, manganese, titanium, cobalt, nickel, vanadium, copper, and zinc. Thereafter, multivariate statistical techniques were employed to process the data, that are known as cluster analysis and discriminant analysis. The former algorithm was applied in order to classify the elements of the soil sample into geochemically homogeneous groups that could be correlated with underlying lithologies. A discriminant analysis was then per formed to statiscally evaluate the distinctiveness of groups arrived at, and at the same-time to define those chemical elements which were most determinant throughoot the discriminatory process. Cluster analysis classified the soil sample elements into eight homogeneou groups that are perfectly correlated with underlying rocks. Discriminant analysis showed that results of the cluster are good, and only titanium and zinc do not play an important role in discriminating the groups arrived at. The results obtained show that the multivariate statistical processing of geochemical soil data can be used successfully as a useful tool when mapping the geology of tropical areas. Finally, an examination of Pearson correlation coefficients, scatter diagrams and residuals from regression analysis, allowed to explore the possible effect of hydrous iron and manganese oxides and of clay minerals (extra-mineralization factors), in producing the copper and zinc anomalies revealed by the geochemical soil survey, originally. Concentrations of hydrous iron and manganese ox ides and of clay minerals were correlated with concentrations of iron, manganese and aluminum in the soil. The Pearson correlation coefficients and the scatter diagrams of copper, and then of zinc, with iron manganese and aluminum, as well as the reduced major axis regression line of copper on iron, indicated that high, grades of copper and zinc found in the soil sample of Alvo 2 - Corpo 4 are not affected by the extra-mineralization factors considered. Therefore, it is conclude that it is the sulphide mineralization present in the study area that can be held responsible for those high concentrations of copper and zinc.
Acesso aberto (Open Access)
U-Pb (LA-ICP-MS) of detrital zircon and whole rock Nd and geochemical constraints on the provenance, depositional age and tectonic setting of the metasedimentary Piriá Basin, northern Brazil: implications for the evolution of the Gurupi Belt
(Universidade Federal do Pará, 2016-06) LOPES, Elem Cristina dos Santos; KLEIN, Evandro Luiz; MOURA, Candido Augusto Veloso; LUCAS, Fernando Rodrigo dos Anjos; PINHEIRO, Bruno Luís Silva; RODRIGUES, Joseneusa Brilhante; SIMAS, Margarete Wagner
The Piriá Basin (Piriá Formation) is a hemi-graben shaped basin that developed over Precambrian rocks of the Gurupi Belt. The lithological content comprises four interfingered lithofacies: (1) arkose and greywacke with pelite layers, (2) laminated siltstones and pelites, (3) arkose with hummocky stratification, and (4) oligomictic conglomerate. This sequence was formed in alluvial fans (conglomerate), and fluvial systems (arkose, greywacke, siltstones and pelites) that were established and evolved during the migration of the subsidence. The sedimentary sequence underwent anquimetamorphism and very weak tectonic deformation. U-Pb analyses of detrital zircon set the maximum depositional age at 591 Ma and indicate several sediment sources, that range in age from the Neoproterozoic to the Archean. The main sources are from the Rhyacian, which is the main period of continental crust formation in the São Luís cratonic fragment and the basement of the Gurupi Belt. Neoproterozoic sources were important in the eastern segment of the basin. Ages from unknown sources in the region so far have also been recorded. Combined, the U-Pb zircon data, the whole-rock geochemical and Sm-Nd results, and the petrographic information revealed proximal felsic to intermediate provenance, in addition to recycled sedimentary sources. As a whole, our data suggest that the Piriá Formation was deposited in a post-orogenic basin related to the final stage of evolution of the Brasiliano cycle of orogenies, which built up the Gurupi Belt.