Navegando por Orientadores "PINHEIRO, Roberto Vizeu Lima"

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O arcabouço estrutural da região de Chega-tudo e Cedral, noroeste do Maranhão, com base em sensores geofísicos
(Universidade Federal do Pará, 2002-12-05) RIBEIRO, José Wilson Andrade; ABREU, Francisco de Assis Matos; http://lattes.cnpq.br/9626349043103626; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The central-northern continental segment of the Brazilian coast, which straddles the boundary between the Pará and Maranhão States, is known in the geological literature as the Gurupi Region. The region is characterized by the presence of two main erosional Precambrian windows which expose small-sized Proterozoic shields in Phanerozoic sedimentary basins. Advances in the understanding of the Precambrian geological history of this area have been limited by the lack and quality of exposures due to the deep weathering profile developed. The use of airborne geophysics proved to be a helpful tool allowing a better definition of some lithological contacts and the shape of major tectonic features. The study area covers part part of the Gurupi Shear Belt, located in one of the Precambrian windows mentioned. This segment of the belt exhibits a variety of sedimentary- and igneous-derived supracrustal rocks in association with plutonic-derived metamorphic rocks. These rocks are structurally organized in three main NW-trending strips which were correlated to the Maracaçumé Complex, Gurupi Group and Tromai Suite. Sheared- and hydrothermally-altered basic and ultrabasic intrusive rocks are often found tectonically interlayered with the Gurupi Group rocks. All the above-mentioned rocks have been metamorphozed under low green-schist to low amphibolite facies conditions and affected by hydrothermal alteration. Diabase dikes crosscut the main Precambrian lithological units along several structural trends. Alluvial deposits along active drainages constitute the youngest lithologic units in the area. The kinematic and geometric analysis of the main tectonic structures observed allows the definition of the area as a shear-belt segment, characterized by steeply-dipping planar structures which are indicative of an oblique left-hand continental collision. The area is also characterized by the presence of a relatively narrow NW-trending highlystrained zone developed along carbonaceous metapelitic lithologic units. This corridor is well defined in the geophysical data and represents an important zone of crustal weakening responsable for most of the deformation partitioning which took place in the area. A secondary NNW-trending shear zone branches off from this main deformation zone and follows the contact of the metapelites with the metavolcaniclastic rocks. The splay caused the detachment of the coarse-grained volcanic rocks from the metapelites. The dominant NW-trending tectonic fabric observed along the exposed rocks of the belt is crosscut by three main sets of fractures well defined by the geophysical surveys, trending N-S, EW and NE-SW. The N-S and E-W fracture sets are associated with drag folds showing sinistral and dextral displacements, respectively. The E-W faults correspond to those previously described by several authors as strike-slip faults. On the scale used, no displacement along the NE-trending fractures could be observed in the geophysical maps, although they control the main river courses in the study area. The NEtrending fractures themselves are not outlined in the magnetic data. In function of this, the available data can not support the idea of some authors who described them as major fault zones related to the the main devolopment of the belt. The N-S fault zones disrupt the NW-trending dominant fabric of the belt exibit left-hand displacements. The N-S, NW-SE and NNW-SSE tectonic fabric present in the region show multiple disruptions, crosscutting one another probably due to several reactivation episodes. The crosscutting relations observed in the geophysical data suggest the N-S fault zones are later in relation to the main NW-trending structures of the belt, although their timings could not be defined with the available data.
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Caracterização estrutural da borda sudeste do sistema transcorrente Carajás com ênfase nas rochas do terreno granítico-gnáissico
(Universidade Federal do Pará, 2002-04-05) OLIVEIRA, Junny Kyley Mastop de; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The Itacaiúnas Belts is placed in the east board of the Amazonian Craton. It is dividid into two main tectonic domains: (1) the Carajás and Cinzento Strike Slip systems that expose Archaean and Proterozoic volcano-sedimentary rocks; and (2) several sets of imbricated thurst fans covering the large basement area. The Carajás Strike Slip System (CSSS) is formed by sets of interrupted, anastomosed lineament, trending around the E-W direction, where both acid and basic volcanic rocks together with ironstones, quartzites (Grão Pará Group); sandstones, mudstones (Águas Claras Formation) and conglomerates (Gorotire Formation) are present inside a kilometer-scale dilational jog. These rocks cover the granitic-gneissic rocks of the Archaean basement. Proterozoic granites are intruded in almost all these rocks forming several plutons. The CSSS is cut by the Carajás Fault representing the most important particular structural feature associated to the Archaean tectonic evolution of the region. The basement of the region, exposed to the south of the CSSS is affected by an early ductile sinistral transpressional event of deformation able to develop a foliation on the rocks. A later ductile-brittle deformational event is overprinting the early mylonitic fabric. This feature has been related to an important hydrothermal episode of alteration including several pulses. On the basis of this general tectonic setting was defined the main aim of this research is which related to the presence of the later planar and linear ductile-brittle fabrics that overprint the early ductile foliation of the basement rocks. The occurrence, age and role of this earlier fabric in the tectonic evolution of the region is not well known. Previous studies have shown the close relation between this deformational feature and the presence of important ore deposits (mainly Au and Cu) distributed along the area. The studied area is located in the SE board of the CSSS, in the basement terrain and is geographically limited by the coordinates 6º 19'56'S; 6º 3508'S and 49º 4913"W; 50º 16'36"W. This study was developed by 1:50.000 scale geological mapping, 3 supported by remote sensing techniques, focusing the geometry and kinematics of the related structures, and also detail scale mapping (1:100) of selected areas and outcrops. The mapping revealed the presence of rocks from the Pium Complex (granolites; about 3.0Ga); Xingu Complex (gneisses, granitoids, amphibolites and migmatites; 2.8Ga); Plaque Suite (biotite — granites; 2.7Ga); Grão Pará Group (basalts, amphilolites, quatzites and ironstones; 2.7 Ga); Proterozoic Granites (2.0-1.8Ga). The Pium and Xingu complexes and Plaque Suite rocks are marked by the presence of an important milonitc foliation trending about the E-W, WNW-ESE and N-S directions always stepling dipping (>70º). The E-W trendding foliation is the most important. This fabric is better represented by a spaced, disjunctive, anastomosing, sometimes smooth foliation closely associated to several milonitic features. This foliation is associated to a partitioned ductile transpressional episode of deformation developed under both sinistral (more important) and destral displacements. A second non-pervasive planar-linear deformational fabric is observed overprinting the early milonitic one. This features are present in both basement and supracrustal rocks (mainly the Grão Pará Group) where this early fabric may be not present. This new foliation is a brittle cleavage that can reach different stages of development from a coarse brechia placed along fault zones to a spaced disjunctive cleavage (from a typical fracture cleavage to a slaty cleavage) along shear bands. This foliation may be accompanied for a structural constructed lineation (slickenlines and slickensides). The general orientation of this set of foliation places around the NW-SE and NE-SW directions, most of them along the first trend. This fabric is associated to a sinistral-dextral transpressional deformational event, able to reativate part of the early milonitic one. Hydrothermal mineral assemblages forming veins fills the shear bands and associated features. This fabric is supposed to be formed by cataclastic flow during high fluid-pressure along tectonic conducts related to the Carajás Fault reactivation during its nucleation about 2.7Ga.
Acesso aberto (Open Access)
Estudo da geometria e cinemática das rochas sedimentares arqueanas da mina do Igarapé do Azul – Carajás-PA
(Universidade Federal do Pará, 2006-09-18) SILVA, Daniela Cristina Costa da; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The Igarapé Azul Mn Mine is geologically situated along the Carajás Fault trace, in the central portion of the Carajás Strike-slip System. The Mn ore deposit is related to politic sedimentary rocks of the Azul Member on the basal portion of the Águas Claras Formation (Archaean). This unit overlain unconformably the Grão Pará Group (Nogueira et al., 1995). At present day three explotation pits are opened in the mine: (1) Main Mine (Mine 1); (2) Mine 2 and (3) Mine 3. In these locations excellent outcrops of siltstones intercalated with finegrained mudstones, sandstones and Mn-layers are exposed. These rocks are organized in folds and normal/reverse faults sets under heterogeneous deformation, partitioned in different scales. The geologic sections exposed in the mines show the dominance of siltstones intercalated with mudstones in contact with pelitic manganesiferous rocks and ore (Mn bioxide). Primary structures such as hummocky stratification, cross stratification and parallel laminations are common in these rocks. Bedding with thickness of centimeters to a few meters (30-50 cm) represents the main primary structure, used as the main deformation marker observed in rocks. The Igarapé Azul Mn Mine is divided into two blocks separated by normal fault with displacements of tens of meters, where the north block is up in relation to the south one. The south block is poorly deformed, with irregularities in bedding which dips at shallow angles towards south, subsequently positioning the ore layer in deeper levels at S direction. In the north block bedding shows heterogeneous behavior. Deformation is more expressive in this region, with the ore deformed by folds and reverse faults. Faults show vertical along-dipping kinematics with dextral conjugated displacements of oblique character. This region can be defined as a major strain corridor. The kilometer-scale corridor observed at the north block follows the NW-SE trend, in concordance with the main domains separated by the faults described above, characterized as curvilinear asymmetric folds with NW and SE shallow plunge axes (10º-25º). These folds are sectioned by sinuous NW-SE and/or E-W normal faults with shallow dips (10º-30º) associated with dextral strike-slip faults, which generate drag folds. Straight or sinuous NW-SE reverse faults and sub-vertical fault zones are observed. The individual folds in this area are flexural reverse structures with en echelon geometry and similar orientation to the curvilinear folds: shallow SE plunging axes. The features described above drawn a gentle kilometer-scale antiform, which results from bedding accommodation in response to the faulting deformation. The parallelism of the features observed in the Igarapé Azul Mn Mine and the main lineaments which drawn the Carajás Fault suggest a close relation between important deformational episodes occurred during the tectonic history of the Carajás Fault. Faults with normal kinematics associated to directional dextral component of displacement are the major exposures in the area and are related to the dextral transtensional episode responsible for installation of the Carajás Fault prior to 2.6 Ga (Pinheiro, 1997). Folds, thrust faults and subvertical fault zones would be related to deformation under sinistral transpressional regime; a second event responsible for the reactivation and tectonic inversion of most of the primary structures near the Carajás Fault zone (Pinheiro, 1997; Pinheiro e Holdsworth, 2000; Lima, 2002).
Acesso aberto (Open Access)
Evolução tectônica da terminação leste da falha Carajás, sul do estado do Pará
(Universidade Federal do Pará, 2002-06-18) LIMA, Fabrizio Dias; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
Acesso aberto (Open Access)
Geometria e história, cinemática do segmento setentrional da Faixa Paraguai, na região de Cáceres/ MT
(Universidade Federal do Pará, 2011-09-21) ALENCAR, Luiz Daniel Castro de; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The Paraguay Belt, at the southern edge of the Amazonian Craton, represents a set of supracrustal Proterozoic sedimentary subjected to positive tectonic inversion with excellent exposures in the vicinity of the Cáceres region, Mato Grosso, where these rocks are deformed show the context surrounding zones and folds failures. In the study area were identified rocks of the Araras Group: thin limestones and shales (Training Guide) dolomitic breccias (Serra do Quilombo Formation) and sandy dolomites, fine sandstones (Noble Training) Group and the Upper Paraguay River: sandstones and mudstones (Training Raizama ) and conglomerates, sandstones and mudstones (Diamond Formation). These rocks of the regional point of view presented in a set of holomorphic folds at various scales, axes subparallel to show the architecture of this broad curve orogen in map view. In mesoscopic structure that stands out is the sedimentary layering (S0) that show since subhorizontal (5 ° to 8 °) to subvertical (84 ° to 88 °), with dominant dip towards the NE and NW quadrants. Minor folds, metrics, occur occasionally, with axis trims with low to moderate NW to NE, verging from SE to NW. The mineral stretching lineations, when present, have low trims (20 °) to NE. The shortcoming are reversed and oblique directional, with high dips to SW and NW quadrants, which are contained grooves with trims low (14 °) to moderate (36 °) for the SW quadrant, associated with dextral kinematic component in general. The fractures are almost always present with subvertical NW-SE direction. Tension gash type fractures were observed in thin limestone Training Guide. These fractures are common in the regions flanking folds, with asymmetries indicating dextral shear. Hydraulic breccia are observed in the carbonate rocks and apparently concentrated near areas of hinges of folds. Based on the relation between plane-lineation of bedding, the geometry of folds and brittle elements of plot, it is suggested that these rocks were affected by a system of oblique compression, coupled with a directional component dextral taking the block and climbed over the W where the coaxial component shows become predominant. The partition of the deformation is evidenced by the ratio folds and mineral stretching lineation, where there are corridors that have distinct deformational shear components (pure and simple) and alternating field between a component and another. This compartmentalization of the components of pure shear and simple geometric arrangement associated with the observed structures are the main inducer of a table partitioned transpression, dextral kinematics, developed on supracrustal rocks, subjected to an oblique compression. This complexity of structural organization within the range reflects the geometry resulting in an arc or assumed during the Neoproterozoic collisional event.
Acesso aberto (Open Access)
Geometria, cinemática da história tectônica das rochas da Serra Norte, Carajás-PA
(Universidade Federal do Pará, 2004) DOMINGOS, Fábio Henrique Garcia; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The studied area is located on northeast portion of the Carajás Strike-Slip System, it corresponds to plateaus of Serra Norte, where the CVRD acts in iron ore mining. On this region there are chemical sedimentary rocks (banded iron formation) and volcanic rocks of the Carajás and Parauapebas formations (Grão Pará Group) respectively, with age of 2.759 ± 2 Ma U/Pb in zircon (Machado et al., 1991). Previous structural geology studies done in the region indicated recumbent folds with fold axis dipping at low angles to NW. These folds are pointed to be the main structures controlling the arrangement of rocks in the area. The present work indicates mutually adjusted folds in different scales. Centimetric folds are parasitic being present in limbs of asymmetric folds with metric size. That corresponds to layering folded, varying from open to isoclinal with axial plane striking NWSE and dipping with low angles to SW-NE. The folds are concentrated in zones ranging from dozen to hundred meters wide striking NW-SE with different shortening measure. Kilometer scale folds are featured by layering drawing a J shape fold in map view. This fold is recumbent with direction parallel to the minor scale folds observed in the region. There are two types of contacts between iron ore and volcanic rocks: (1) normal concordant folded contacts and (2) fault contacts. The rocks studied in the area were regionally deformed by transpression with simple shear dextral component and pure shear component, dominated by shortening from NE to SW. This is based on vergence sense, fold asymmetries and general trend of the mapped structures compared to the E-W regional trending of the Carajás Strike-Slip System. The deformation is particularly concentrated in NW-SE zones trending that follow the trace of major discontinuities, converging from the Carajás Fault. The deformation responsible for the geometric and kinematic history of the rocks takes place during transpressional sinistral deformation affecting all Carajás Strike Slip System, between 2.6 and 2.0 Ga.
Acesso aberto (Open Access)
Geometria, cinemática e modelamento tectônico das rochas do Grupo Vila Nova, região de Pedra Branca do Amapari – AP.
(Universidade Federal do Pará, 2009-05-25) CAVALCANTE, Geane Carolina Gonçalves; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The studied area is located at Pedra Branca do Amaparí region, center south Amapá state, at about 190 km from Macapá. The rocks exposed in this region comprise Palaeoproterozoic granites (Lafon et al., 2008) and greenstone belts related to Vila Nova Group. The Vila Nova Group represents a Palaeoproterozoic greenstone belt metamorphosed and deformed under greenschist to amphibolite facies conditions. This Group belongs to the Maroni-Itacaiúnas Province setting, in the eastern boundary of the Guianas Shield. The data obtained in this research point to the presence of ductile and brittle fabrics elements such as spaced and continous foliations, flexural, tight, open parasitic and isoclinal folds, structural and mineral lineation, kink bands and oblique to normal faults. Foliations are the main structures and display anastomotic patterns with a N-S and NE-SW preferred orientation. They have shallow to steep dips mainly to NW and SE. Flexural folds occur in the banded iron formations and amphibolitic rocks in centimeter to meter scale, with shallow to moderate plunging axes (12º to 50º) to NW, NE and SW. Stretching lineation is defined by elongation of quartz grains and shows shallow to steep plunges generally to NW. Boudins are also defined by quartz grains and normally occur between banded iron formation foliation planes, where they configure sigmoidal features. The data obtained suggest that the rocks composing the Vila Nova Group were deformed in consequence of diapirism of adjacent granite plutons, associated with partitioned transpression in the post-diapirical state when occurred compartimentation between simple shear and pure shear components. Transpression shows a sinistral component of simple shear and a E-W shortening pure shear component.
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Partição da deformação no limite entre o terreno granito-greenstone de Rio Maria e o Cinturão Itacaiúnas, Carajás (PA)
(Universidade Federal do Pará, 2009-05-22) VIEGAS, Luís Gustavo Ferreira; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
This research is primarily concerned with the tectonic evolution of an Archaean crustal segment of the Amazonian Craton which is thought to encompass two distinct Archaean terranes: the Rio Maria Granite-Greenstone Terrain, to the south, and the Itacaiúnas Belt, to the north. These two terranes show similar lithologies and a short range variation in geochronological ages, but their structural pattern differs significantly. The rocks exposed in the domains of the Rio Maria Granite-Greenstone Terrain comprise mainly TTG series (2.9 – 2.86 Ga), alkaline plutons (2.86 Ga) and greenstone belts (2.9 Ga), which display ages older than those found on the Itacaiúnas Belt. A compositional layering can be seen in the tonalites, trondhjemites and granodiorites, and a magmatic foliation is locally observed in the monzogranites and syenogranites. These fabrics strike NW-SE to E-W with medium to shallow dips to NE and SW. The linear fabrics associated with these structures are only locally developed, and generally show shallow plunges to SE. In the Itacaiúnas Belt the main structural feature is a coarse mylonitic foliation present in the tonalites, granodiorites and migmatites associated with the Xingu Complex (2.7 Ga), and also in the syenogranites and alkali-feldspar granites of the Plaquê Suite (2.7 Ga). This foliation is steeply dipping to N and S, trending E-W to NW-SE. The stretching lineation present in the mylonitc foliation planes shows shallow dips to NE, SE, NW and SW. Five structural domains were defined based on strain facies analysis method. From north to south, these facies show partition of displacement into compressional and strike-slip components and also distinct fabric generation patterns. Facies V and IV, located in the southern portion of the studied area, are characterized by a dominant compressional component of frontal to oblique nature associated with structures generated by magmatic to submagmatic flow. The central portion of the study area is marked by facies III, which represents a junction between different structural patterns and fabric generation processes. This facies shows interplay between compressional and strike-slip displacements, as well as fabrics developed either by magmatic flow and solid-state flow. The northern portion of the studied area comprises facies II and I, which contain fabrics derived mainly from plastic strain associated with a high degree of planar transposition. The overall kinematic pattern is mainly sinistral, with dextral displacements observed where the compressional component of partitioned transpression is stronger. The two northern facies display sinistral displacement, while facies III and facies IV show a combination of compressional and transcurrent motion. Local shear sense indicators suggest sinistral displacement for facies V. The geological evolution of the studied area involved two main stages: i) a first stage of emplacement of TTG granitoids in an Archaean protocrust mainly located at the region of Rio Maria Granite Greenstone Terrain, and ii) a second stage marked by shear zone nucleation, magma generation and pluton emplacement in a partitioned transpressional setting. The partitioned transpression was responsible for nucleation of a regional scale set of shear zones which partitioned the deformation across the area. In the northern facies, the deformation pattern is mainly characterized by strike-slip transposition of planar fabrics formed under solid state conditions. To the south, magmatic flow is dominant and compressional components of transpression are evident. The regional shear zones also worked as conduits for magma ascension and emplacement at higher levels of the crust. These magmas were derived from partial melting of the TTG series and are mainly alkaline and/or migmatitic in composition. The structural pattern observed in the area between the Rio Maria Granite-Greenstone Terrain and the Itacaiúnas Belt is interpreted as a result of progressive deformation in a sinistral partitioned transpressional setting. This strain pattern comprised geometric and kinematic partitioning in zones of strike-slip displacement and compressional components, and also distinct fabric generation patterns ranging from magmatic to solidstate flow. These characteristics suggest that these two terranes are involved in the same transpressional event and, as such, the Itacaiúnas Belt can be interpreted as a crustal fragment associated with the Rio Maria Granite-Greenstone Terrain, which evolution is marked by progressive events of tectonic reworking and granite emplacement.