Navegando por Assunto "Nordeste do Brasil"

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Aplicação de tratamento estatístico multivariante em dados de perfis de poços da Bacia de Sergipe-Alagoas
(Universidade Federal do Pará, 1991-09-27) BUCHEB, José Alberto; EVANS, Hilton Bernard
A series of multivariate statistical techniques (cluster, principal component and discriminant analysis) was tested and applied to well log data from the Camorim field (offshore Sergipe State, Brazil) in order to identify facies previously defined through core description. The second step in the process of facies determination was supported by auxiliary methods (compositional and sequence facies analysis), which produced better results in the calibration of rock-log data, when combined with the multivariate techniques. The facies determination, once established, permits the refinement of the process of formation evaluation, enabling the examination of each facies separately. This procedure made it possible to choose, for each lithology, the parameters used in log interpretation. In parallel, this process allowed the summation of thickness, porosity, fluid saturation and the adoption of different cut-offs for each group, separately. Other applications included: enhancement in the estimation of porosity and permeability, the adaptation of algorithms designed for fast porosity estimation, the mapping of variables useful in the characterization of the vertical variability of the reservoir rocks and the automatic generation of stratigraphic sections. Finally, the possibility of integration of the work from this study with statistical systems of reservoir description, other facies determination techniques currently being developed and the utilization of multivariate statistical methods in well log data, as an auxiliary exploratory tool, were illustrated.
Acesso aberto (Open Access)
Aspectos texturais do magmatismo e tramas da tectônica impostas ao Granito Chaval na Zona de Cisalhamento Santa Rosa, extremo Noroeste da Província Borborema
(2014-12) GORAYEB, Paulo Sérgio de Sousa; LIMA, Aline Maria Meiguins de
The Northwestern region of Borborema Province features a wide variety of granitic bodies with diverse nature and tectonic evolution, since the Paleoproterozoic to Early Paleozoic, presenting higher incidence related to Neoproterozoic emplaced at different stages of Brasiliano (Panafrican) orogeny. One of these examples is the Chaval Granite representing a batholith body intruded in orthogneisses of Granja Complex and supracrustal rocks of Martinópole Group, outcropped near the Ceará and Piauí Atlantic coasts, Northeastern Brazil. The batholith is partly covered by Cenozoic coastal deposits and sedimentary rocks of the Paleozoic Parnaíba Basin. The Chaval Granite has a striking textural feature, which is represented by porphyritic highlighting microcline megacrysts in syenogranites and monzogranites, and many others textural/structural features of magmatic origin. They allowed interpreting the plutonic evolution at relatively shallow crustal level emplacement acting processes of fractional crystallization, magma mixing with intense magmatic flow, and gravitational force due to density difference of magma that lead to fluctuation of megacrysts of microcline and plagioclase in the residual magma, and accommodation of small bodies of leucogranite and pegmatites in the final stages of plutonic magmatic evolution of such plutonism. On the other hand, across the Eastern half of the pluton, there is a rich collection of shear structures related to the tectonic construction of the Santa Rosa Transcurrent Shear Zone, which led to tectono-metamorphic transformations superimposed on magmatic features that reached peak metamorphic conditions in the low amphibolite facies. Cartographically, three homogeneous structural domains were individualized, and each of them presents a variety of petrographic-structural features of the Chaval of igneous or tectonic nature. The plutonic rocks were deformed and progressively modified Eastward, in which the rocks change to darker gray, and comminution and dynamic recrystallization processes are reduced, as well as the coarse-grained granites are progressively, as well as the size of the phenocrysts to thinner dimensions, keeping their porphyroid characteristics, being accentuated the mylonitic features to achieve the main portion of Santa Rosa Transcurrent Shear Zone. As main structural features, there is the ondulatory extinction, cleavage and twining bending, twinning deformation, anastomosing foliation, badinage, S-C foliation, mineral stretching lineation, rotated and segmented crystals, lenticular, almondy or fish forms of porphyroclasts, pressure shadow, and ribbon quartz. The products of this shear deformation result in the formation of protomylonites, mylonites, and ultramylonites. These mylonite zones represent areas with the highest concentration of deformation that can gradually follow their textural and mineralogical changes, setting up a classic sequence of progressive heterogeneous deformation by simple shear in brittle-ductile and ductile conditions. The emplacement of Chaval Granite happened at the end of the Cryogenian (approximately 630 Ma) and can be interpreted as syn-tardi tectonic magmatism regarding the Brasiliano event. The process that generated the Santa Rosa Shear Zone resulted from lateral extravasation crustal masses in ductile flow took place in the final increments of deformation of a continental collision on an oblique thrust system, which built the Northwest Ceará Shear Belt, and happened at the end of Brasiliano (Panafrican) orogeny in Northwest Borborema Province.
Acesso aberto (Open Access)
Cruentas guerras: índios e portugueses nos sertões do Maranhão e Piauí (primeira metade do século XVIII)
(Universidade Federal do Pará, 2011-08-19) MELO, Vanice Siqueira de; CHAMBOULEYRON, Rafael Ivan; http://lattes.cnpq.br/7906172621582952
In the captaincies of Maranhão and of Piauí, in Portuguese America, there were many wars against Indians throughout the first half of the eighteenth century. This dissertation discusses how the space of these captaincies was described in colonial texts, as well as how the troops contributed to transform the landscape of the region. This dissertation examines how the colonial landscape was composed both by the Indians spaces and by the relationship that indigenous groups established with each other and with Luso-brazilian settlers. This dissertation also discusses how the wars were part of power relations within the State Maranhão and Grão-Pará and how their occurrence depended on specific political interests.
Acesso aberto (Open Access)
Diásporas de encantados na Amazônia Bragantina
(2015-06) SILVA, Jerônimo da Silva e; PACHECO, Agenor Sarraf
Starting from ethnographic exercises, the text presents diasporic experiences of women mourners that when migrating from northeastern Brazil to “Amazon Bragantina”, in Pará State, from the 1950s, whose lives were marked by the initiation process with the entities of the Brazilian enchant (Prandi, 2004). On overnight trips to cemeteries, transfiguration, physical transport, clairvoyance and wanderings in animal bodies, winds and waters, these mourners revisited “worlds” and ancient “times”, going to talk with shamans and “powerful” chanters of Maranhão, Paraíba, Piauí and Ceará, letting people see and delighted in other senses of displacement. The belief in the ability of entities to monitor persons holding the “gift of praying” to the Pará, as well as continually transitioning these sites, nomadizando up (Deleuze; Guattari, 1995) between “there” and “here”, constitute the phenomenon of “diaspora of the enchanted” (Brah, 2011; Hall, 1999, 2009). Living with these women teaches, among other things, to defend conceptions of meetings and displacements of cultures that perceive the radical otherness of the cosmology of the human sciences, even when one believes this faithfully situated in places of departure, passage and arrival of movements, forgetting often it is not the place, but the material and symbolic transits.
Acesso aberto (Open Access)
Geologia e metalogênese do ouro do greenstone belt da Serra das Pipocas, Maciço de Troia, Província Borborema, NE - Brasil
(Universidade Federal do Pará, 2018-12-13) COSTA, Felipe Grandjean da; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
At the Archean–Paleoproterozoic Troia Massif, in Borborema Province, NE–Brazil, two major Paleoproterozoic greenstone belts are recognized (Algodões and Serra das Pipocas). These share similar ages and lithostratigraphic characteristics with other 2.2–2.1 Ga greenstone belts of the surrounding cratonic domains (e.g. Guiana shield and São Luis–West Africa craton), and also host gold mineralization. In this thesis, a U–Pb zircon age of 2185 Ma was obtained for a pre–collisional metatonalite (Mirador tonalites) with geochemical affinity similar to adakites–like rocks. For syn– to post–collisional potassic plutons (Bananeira suite) we obtained U–Pb zircon ages of 2079 Ma for a deformed quartz monzonite and of 2068 Ma for the less–deformed equigranular granite. These granitoids of the Bananeira suite are both of high–K calc–alkaline affinity, and probably derived from partial melting of crustal sources. Zircon Hf crustal model ages of all granitoids range between 2800 and 2535 Ma, indicating that Archean crustal components contributed to their magma genesis. However, two analyzed c. 2.3 Ga old inherited zircon grains showing Ɛ_Hf (t) values of c. +4.9, indicate that crustal reworking of less–radiogenic Paleoproterozoic sources also participated. Gold mineralization in the Serra das Pipocas greenstone belt is associated with a regional NE-trending shear zone. The mineralized areas (the Pedra Branca gold deposit) are located near–parallel to the stratigraphy, siting on shear zones, between metavolcanic and metasedimentary unit boundaries. The main stage of gold mineralization is found in association with quartz veins, high–temperature calc–silicate alteration (diopside, K–feldspar, amphibole, titanite, biotite, pyrite, albite, magnetite ± carbonates) and albitization. Free–milling gold commonly precipitates in close association with magnetite and gold/silver tellurides. Two fluid inclusion assemblages were identified in mineralized quartz veins. Assemblage 1 is characterized by pseudo–secondary trails that show the coexistence of CO₂–rich and low salinity (0 to 8 wt% NaCl equiv.) CO₂–H₂O–NaCl and H₂O–NaCl inclusions, suggesting formation during phase separation (fluid immiscibility). The mean isochores intersection of CO₂–rich and H₂O–NaCl inclusions of assemblage 1 suggests PT conditions of 495 °C and 2.83 kbar (c. 10.5 km depth), akin to hypozonal orogenic gold deposits. Assemblage 2 is represented by late secondary low–temperature (Th<200°C) H₂O–NaCl inclusions, probably unrelated to gold mineralization. The δ¹⁸O, δD and δ¹³C values of hydrothermal minerals (quartz, calcite, biotite, hornblende and magnetite) define fluid δ¹⁸O values ranging from +8.3 to +11.0‰ (n=59), fluid δD from -98 to -32‰ (n=24) and δ¹³C values of calcite from -6.35 to -9.40‰ (n=3). Oxygen isotope thermometry for quartz–magnetite pairs gave temperatures from 467 to 526°C (n=7, average 503°C), which probably represents the temperature of gold deposition. The association of gold with magnetite and tellurides strongly suggests an ore–forming fluid sourced by oxidized magmas, similar to those interpreted as ‘orogenic oxidized intrusion– related gold deposits’ in other Precambrian greenstone belts (e.g. Abitibi and Eastern Goldfields). Four deformation events (Dn, Dn+1, Dn+2 and Dn+3) are recognized in the Serra das Pipocas greenstone belt. The Dn event is responsible for the early Sn foliation, parallel to bedding (So) of the greenstone pile. The Dn+1 event is characterized by a pervasive, southeasterly–dipping Sn+1 foliation that is axial–planar to a number of asymmetric, tight to isoclinal and recumbent folds. The Dn+2 event represents a transcurrent deformation phase and the late Dn+3 event is characterized by ductile–brittle deformation. The main stage of gold mineralization is found as deformed quartz veins and associated high–temperature alteration, but some lower temperature gold (±Te, Ag) occurrence along the late stage brittle structures (Dn+3 event) is also observed. The U–Pb titanite age of 2029 ± 28 Ma for the high– temperature calc–silicate alteration (and gold mineralization) is presented here. However, the strong Pb loss of titanite grains defines a 574 ± 7 Ma lower intercept age, evidencing that early gold mineralization were broadly affected by Neoproterozoic deformational events and metamorphism (Brasiliano/Pan–African orogeny). The U–Pb zircon age of 575 ± 3 Ma for syn–tectonic diques bracketed the age of late Dn+3 deformation event. Then, the progressive deformation recorded (Dn+1, Dn+2 and Dn+3) is probably of Neoproterozoic age, with the maximum compressive stress (ζ1) in the WNW–ESE direction. However, at local scale, Paleoproterozoic deformation records (Dn) still preserved. The genetic model for the Pedra Branca gold deposit is suggested here by a two–stage exhumation–drive gold mineralization; represented by a (1) early oxidized hypozonal orogenic gold mineralization (main stage) that occurred at c. 2029 Ma, shortly after the high–grade Paleoproterozoic metamorphism and first exhumation processes of the greenstone pile, and later on, at c. 580 Ma, a (2) late gold mineralization (remobilization?) occurred at shallow levels (second exhumation process) associated to late Neoproterozoic Brasiliano/Pan–African orogeny.
Acesso aberto (Open Access)
Interpretação quantitativa de anomalias gravimétricas ar-livre da margem continental norte brasileira, setor nordeste
(Universidade Federal do Pará, 1990-10-12) CASTRO, David Lopes de; BISCHOFF, Jürgen H.
Free-air gravity anomalies across continental margins of passive type present a general standard form. This form can be well explained by a distribution of simple horizontal two-dimensional discontinuities. An automatic process of random search was proposed for quantitative interpretation of the data. Using the method of flexible polyhedron (Simplex), the main parameters of the model were estimated, considering a convenient ration between number of points/number of parameters to be determined. The free-air gravity anomalies over the region of the continental slope can be explained by a single horizontal discontinuity (simple step) and, as the wavenumber domain has information about this anomaly, it was also proposed an iterative graphic procedure for the analysis of the amplitude spectral response for the anomalies. Applying the Fourier transform, it would possible to determine the depth and the off-set of this discontinuity, and, once these parameters are measured, the density is calculated. The basic aim for studying these procedures was to combine the two methods of interpretation in the space and wavenumber domains, in order to obtain a more constrained solution to the geological structure of the studied area. The two interpretative procedures discussed above were applied and their respective capacity of resolution were analysed, over the free-air gravity anomalies of profiles across the continental margin of northeast Brazil, covering the states of Maranhão to Rio Grande do Norte. The survey, called Project EQUANT I, LEG 1, was carried out during the period of August 27 to October 10, 1987, by the Oregon State University (OSU) using the oceanographic ship Prof. W. Besnard of the Oceanographic Institute of São Paulo University (USP). It was demostrated that the inversion done directly in the space domain is more favorable for the interpretation, even for typical anomalies, although the treatment in the spectral domain is relatively simpler.
Acesso aberto (Open Access)
Padrões de distribuição da avifauna em área de Ecótono Cerrado-Caatinga no Nordeste do Brasil
(Universidade Federal do Pará, 2015) GONÇALVES, Gabriela Silva Ribeiro; OLIVEIRA, Arthur Ângelo Bispo de; http://lattes.cnpq.br/1100433822757573; SANTOS, Marcos Pérsio Dantas; http://lattes.cnpq.br/7941154223198901
Acesso aberto (Open Access)
Paleomagnetismo de rochas vulvânicas do Nordeste do Brasil e a época da abertura do Oceano Atlântico Sul
(Universidade Federal do Pará, 1983-12-28) GUERREIRO, Sonia Dias Cavalcanti; SCHULT, Axel
In the first part of this paper palaeomagnetic and rock magnetism investigations were developed in volcanic samples from the Northeast of Brasil. The age of the samples spans the Jurassic and Cretaceous periods. To accomplish this task four areas were studied and a total of 495 samples from 56 cites were analyzed. A portable drilling machine with 2.5 cm core diameter was used to collect the samples. The orientation of the samples were obtained by means of a magnetic compass, and a clinometer. The specimens were submitted to alternating field demagnetization and in, a few cases, to thermal demagnetization. Giving unit weight to each site the mean direction of the characteristic remanent magnetization of each one of the studied areas were determined. The volcanic rocks from Jurassic, lying in the western part of the Maranhão Basin (Porto Franco - Estreito) , yielded the mean direction: declination D=3.9º, inclination I=-17.9°, with the circle of 95% of confidence α95=9.3º, precision parameter k=17.9, number of sites N=15. All sites showed normal polarity. For this area was determined a palaeomagnetic pole with coordinates 85.3°N, 82.5°E (circle of 95% of confidence A95 = 6.9º) that is situated near other known palaeomagnetic poles for this period. The Lower Cretaceous rocks from the eastern part of the Maranhão Basin (Teresina-Picos-Floriano) yielded a mean direction for the characteristic remanent magnetization having D= 174.7º, I=6.0°, α95=2.8º, k=122, N=21. All sites showed reversed polarity. The calculated palaeomagnetic pole associated with these rocks has coordinates 83.6°N, 261.0ºE (A95= 1.9°) and is in agreement with other South American poles of the same age. In Rio Grande do Norte a swarm of Lower Cretaceous tholeiitic dikes was studied having a characteristic mean direction with D= 186.6º, I= 20.6º with α95= 14.0º, k= 12.9, and N= 10. The sites in this area showed mixed polarity. The computed palaeomagnetic pole is located at 80.6ºN and 94.8ºE with A95= 9.5º. The study of the volcanic rocks of the magmatic province of Cape Santo Agostinho yielded the following values for the characteristic remanent magnetization D= 0.4º, I=-20.6º with α95= 4.8º, k=114, N=9. All sites showed normal polarity and the calculated paleomagnetic pole has the coodinates: 87.6ºN 135ºE with A95= 4.5. The secular variation of the obtained directions was discussed so that each pole presented in this paper is really a palaeomagnetic pole. The analysis of the magnetic minerals of these samples was done by thermomagnetic curves and by X-ray diffraction. In most cases the magnetic phase in the rocks is mainly titanomagnetite with poor titanium content. Maghemite and sometimes hematite, usually a product of weathering, did not obscure the initial thermoremanent magnetization of these rocks. Generally the determined Curie temperature lies between 500-600º C. Frequently it was observed that the exsolved titanomagnetite has a phase near magnetite and another phase rich in titanium, near ilmenite, as a result of high temperature oxidation. The second part of this paper deals with the determination of the time of the opening of the South Atlantic ocean by means of palaeomagnetic data. In this paper, however, instead of using the polar wandering paths of the continents (the usual method) statistical tests were applied that give the probability that a certain configuration for the two continents be consistent or not with the palaeomagnetic data for a chosen period. For the Triassic, Jurassic, Lower Cretaceous and Middle-Upper Cretaceous periods the palaeomagnetic poles for Africa were compared with the respective poles of South America in pre-drift configuration by means of an F-test. Other configurations that indicate some separation between the two continents were also tested. The results of the tests showed that the pre-drift reconstruction after Martin et al (1981) is consistent with the palaeomagnetic data for Triassic, but there is a significant difference between the respective Jurassic, Lower Cretaceous and Middle-Upper Cretaceous palaeopoles for the two continents, with a probability of error of less than 5%. Other pre-drift reconstructions were tested and the results were the same. Comparing the pole positions for South America and Africa in a configuration that indicates a small separation between the two continents, as the one suggested by Sclater et al (1977) for 110 m.y.B.P. one finds a significant difference for the Triassic data. For the Jurassic and Lower Cretaceous palaeomagnetic poles, which are, however, earlier than the suggested date of the reconstruction, the results are consistent with that separation of the continents with a probability of error of less than 5%. The reconstruction for 80 m.y.B.P., after Francheteau (1973), indicanting a larger separation between the continents, is consistent with the Middle-Upper Cretaceous palaeomagnetic poles. Assuming the premise of the movements of crustal blocks relative to each other as rigid blocks, the results of the F-test indicated that South America and Africa were close together during Triassic. There was, nevertheless, a small separation between the continents in Jurassic, probably due to an earlier rifting event, and this separation was stationary until Lower Cretaceous time. This result is different from the most part of the papers that discuss the openning of the South Atlantic ocean. The Middle-Upper Cretaceous data are compatible with a fast and significant spreading of the continents in that period.
Acesso aberto (Open Access)
Sobre o sinal de um downscaling dinâmico às oscilações intrassazonais de precipitação no setor norte do Nordeste do Brasil
(2012-07) ALVES, José Maria Brabo; SOUZA, Everaldo Barreiros de; COSTA, Alexandre Araújo; MARTINS, Eduardo Sávio Passos Rodrigues; SILVA, Emerson Mariano da
Intraseasonal oscillations are factors controlling the interannual variability of tropical rainfall. The knowledge of how numerical models reproduce its variability is important to better understand their roles and support operations of weather and climate. This paper investigates the sensitivity of a downscaling dynamic precipitation model in predicting the intraseasonal oscillations observed in the northern sector of Northeast Brazil (SNNEB - 45°W-37ºW and 2ºS-12°S) during the period from 1974 to 2000. The results showed that rainfall was simulated on SNNEB explained more than 70% of the variability of rainfall observed in the quarter February to April in this region. Statistical of averages, standard deviations and percent this quarter, in this region in years of climatic contrasts in the Oceans Pacific and Atlantic Tropical were also well captured by the precipitation simulated by downscaling. Spectral analysis with the use of wavelets showed that dynamic downscaling has the potential to reproduce observed spectral peaks of precipitation in SNNEB scales up to 8 days and the scales between 64 and 128 days for the period January 1 to June 30.