Análise estrutural da deformação cenozóica na Bacia de Cumuruxatiba (BA)

The Cumuruxatiba basin is located at the southern coast State of Bahia in northeastern of Brazil. This basin was formed in distensional context, with rifting and subsequent thermal phase during Neocomian to late Cretaceous. At Cenozoic ages, the Abrolhos magmatism occurs in the basin with peaks during the Paleocene and Eocene. In this period, there was a kinematic inversion in the basin represented by folds related to reverse faults. Structural restoration of regional 2D seismic sections revealed that most of the deformation was concentrated at the beginning of the Cenozoic time with the peak at the Lower Eocene. The post-Eocene is marked by a decrease of strain rate to the present. The 3D structural modeling revealed a fold belt (trending EW to NE-SW) accommodating the deformation between the Royal Charlotte and Sulphur Minerva volcanic highs. The volcanic eruptions have caused a differential overburden on the borders of the basin. This acted as the trigger for halokinesis, as demonstrated by physical modeling in literature. Consequently, the deformation tends to be higher in the edges of the basin. The volcanic rocks occur mainly as concordant structures (sills) in the syn-tectonic sediment deposition showing a concomitant deformation. The isopach maps and diagrams of axis orientation of deformation revealed that most of the folds were activated and reactivated at different times during the Cenozoic. The folds exhibit diverse kinematic patterns over time as response to behavior of adjacent volcanic highs. These interpretations allied with information on the petroleum system of the basin are important in mapping the prospects for hydrocarbons

Deglaciation sequences in the Permo-Carboniferous Itarare Group, Parana Basin, southern Brazil

The Late Carboniferous-Early Permian Itarare Group is a thick glacial unit of the Parana Basin. Five unconformity-bounded sequences have been defined in the eastern outcrop belt and recognized in well logs along 400 km across the central portion of the basin. Deglaciation sequences are present in the whole succession and represent the bulk of the stratigraphic record. The fining-upward vertical facies succession is characteristic of a retrogradational stacking pattern and corresponds to the stratigraphic record of major ice-retreat phases. Laterally discontinuous subglacial tillites and boulder beds occur at the base of the sequences. When these subglacial facies are absent, deglaciation sequences lie directly on the basal disconformities. Commonly present in the lowermost portions of the deglaciation sequences, polymictic conglomerates and cross-bedded sandstones are generated in subaqueous proximal outwash fans in front of retreating glaciers. The overlying assemblage of diamictites, parallel-bedded and rippled sandstones, and Bouma-like facies sequences are interpreted as deposits of distal outwash fan lobes. The tops of the deglaciation sequences are positioned in clay-rich marine horizons that show little (fine-laminated facies with dropstones) or no evidence of glacial influence on the deposition and likely represent periods of maximum ice retreat. (c) 2006 Elsevier Ltd. All rights reserved.

The Serido Group of NE Brazil, a late Neoproterozoic pre- to syn-collisional basin in West Gondwana: insights from SHRIMP U-Pb detrital zircon ages and Sm-Nd crustal residence (T-DM) ages

The Serido Group is a deformed and metamorphosed metasedimentary sequence that overlies early Paleoproterozoic to Archean basement of the Rio Grande do Norte domain in the Borborema Province of NE Brazil. The age of the Serido Group has been disputed over the past two decades, with preferred sedimentation ages being either Paleoproterozoic or Neoproterozoic. Most samples of the Serido Formation, the upper part of the Serido Group, have Sm-Nd T-DM ages between 1200 and 1600 Ma. Most samples of the Jucurutu Formation, the lower part of the Serido Group, have T-DM ages ranging from 1500 to 1600 Ma; some basal units have T-DM ages as old as 2600 Ma, reflecting proximal basement. Thus, based on Sm-Nd data, most, if not all, of the Serido Group was deposited after 1600 Ma and upper parts must be younger than 1200 Ma.Cathodoluminescence photos of detrital zircons show very small to no overgrowths produced during ca. 600 Ma Brasiliano deformation and metamorphism, so that SHRIMP and isotope dilution U-Pb ages must represent crystallization ages of the detrital zircons. Zircons from meta-arkose near the base of the Jucurutu Formation yield two groups of ages: ca. 2200 Ma and ca. 1800 Ma. In contrast, zircons from a metasedimentary gneiss higher in the Jucurutu Formation yield much younger ages, with clusters at ca. 1000 Ma and ca. 650 Ma. Zircons from metasedimentary and metatuffaceous units in the Serido Formation also yield ages primarily between 1000 and 650 Ma, with clusters at 950-1000, 800, 750, and 650 Ma. Thus, most, if not all, of the Serido Group must be younger than 650 Ma. Because these units were deformed and metamorphosed in the ca. 600 Ma Brasiliano fold belt during assembly of West Gondwana, deposition probably occurred ca. 610-650 Ma, soon after crystallization of the youngest population of zircons and before or during the onset of Brasiliano deformation.The Serido Group was deposited upon Paleoproterozoic basement in a basin receiving detritus from a variety of sources. The Jucurutu Formation includes some basal volcanic rocks and initially received detritus from proximal 2.2-2.0 Ga (Transamazonian) to late Paleoproterozoic (1.8-1.7 Ga) basement. Provenance for the upper Jucurutu Formation and all of the Serido Formation was dominated by more distal and younger sources ranging in age from 1000 to 650 Ma. We suggest that the Serido basin may have developed as the result of late Neoproterozoic extension of a pre-existing continental basement, with formation of small marine basins that were largely floored by cratonic basement (subjacent oceanic crust has not yet been found). Immature sediment was initially derived from surrounding land; as the basin evolved much of the detritus probably came from highlands to the south (present coordinates). Alternatively, if the Patos shear zone is a major terrane boundary, the basin may have formed as an early collisional foredeep associated with south-dipping subduction. In any case, within 30 million years the region was compressed, deformed, and metamorphosed during final assembly of West Gondwana and formation of the Brasiliano-Pan African fold belts. (C) 2003 Elsevier B.V. All rights reserved.

Northwestern overthrusting and related lateral escape during the Brasiliano orogeny north of the Patos lineament, Borborema province, northeast Brazil

The Borborema province (BP) of northeastern Brazil, located between the São Luís and São Francisco cratons, represents a branching system of Precambrian orogens of the South American platform. It is composed of segments of Archean and Proterozoic crust that were deformed by the convergence of the West African and São Francisco-Congo cratons during assembly of the Brasiliano collage (650 to 500 Ma), a period of intense orogenic activity considered to be the strongest and most pervasive tectonic event that affected the Precambrian of the South American platform. The tectonic and kinematic history of the Brasiliano/Panafrican orogeny is fundamental for reconstructing South American and African Precambrian geology. The correlation between Neoproterozoic tectonic processes occurring in both continents should use structural elements, of regional or local character, with identical kinematic and metamorphic conditions manifested in both basement and supracrustal units. North of the Patos shear zone, subhorizontal Brasiliano thrusts (0.65 to 0.58 Ga) affected the basement and the supracrustal Seridó belt with such related regional D1/D2 structures as foliation, lineation, isoclinal folds, and related metamorphism. Overprinting the previous structures, regional folding with a vertical S3 foliation and an associated strike-slip shear zone were developed (0.58 to 0.52 Ga). The metamorphism is similar for all deformation phases, ranging from upper-greenschist to amphibolite facies with mineral assemblages including biolite and garnet throughout the Seridó fold belt. We propose, on the basis of deformational and kinematic reconstructions, that the structural evolution of the Seridó fold belt was characterized by transition from a syn-collisional to a strike-slip regime. The transition between regimes occurred, progressively or instantaneously, by the switching of the maximum and intermediary strain axes of the strain ellipsoid. The entire tectonic history can be related to a frontal or oblique collision and lateral escape tectonics, with local, syn-collisional transpression and transtension. The Patos shear zone represents a final vertical shearing, juxtaposing different terranes of the northern and southern Borborema province.

Os granitóides brasilianos da faixa de dobramentos paraguai, MS e MT

The Brazilian Granitic Province from southeastern Mato Grosso do Sul and Mato Grosso region, central western Brazil, can be divided into two major groups and/or magmatic events related to the evolution of the Paraguay Fold Belt. The southern portion crops out in Mato Grosso do Sul State and is constituted by the Taboco, Rio Negro, Coxim and Sonora massifs forming NE-SW oriented, elongated small intrusions. The north portion crops out in Mato Grosso State and is constituted by the São Vicente, Araguaiana and Lajinha batholiths. Lithogeochemical aspects of the northern granites point to Type-I granites ranging from K calc-alkaline to high-K, peraluminous to metaluminous in composition, generated in an environment of continental collision and/or post- collision decompression. The southern granites are Type-I, from K calc-alkaline to high-K, peraluminous to subordinate metalummous, in a syn-collision continental arc environment with the exception of some pre-collisional facies from the Rio Negro Massif. The southern granites have less SiO 2 and K 2O, and are less differentiated and evolved than granites from the northern region. The four southern granites can be grouped into two subordinate sets with the degree of differentiation increasing from South (Taboco and Rio Negro) to North (Coxim and Sonora). The granitic rocks are characterized by a magmatism generated by melting of material from the lower crust which suggests that in this province the formation from non-cogenetic magmas with diversified compositions and distinct degrees of fractioning reaching more steady consolidated environments at the end of the collisional event in the southeastern Amazonian Craton.

Contexto tectônico dos granitóides neoproterozóicos da faixa de dobramentos paraguai, MS e MT

The Neoproterozoic Granitic Province from the southeast of Mato Grosso and Mato Grosso do Sul region is constituted by seven distinctive granitic bodies, emplaced in the epimetamorphic rocks of the Cuiabá Group and related to the evolution of Paraguai Folded Belt. The Northern portion crops out in Mato Grosso State and is constituted by São Vicente, Araguaiana and Lajinha batholiths; the Southern portion crops out in the Mato Grosso do Sul State and is represented the Sonora, Coxim Rio Negro and Taboco massifs. The structural evolution is evidenced by the presence of three deformational phases, the first one is characterized by axial planar foliation (S 1), parallel or sub parallel to S 0, with attitude N60E/70NW; the second constitutes the most important phase for the tectonic arrangement and is defined by a slaty and/or crenulation cleavages (S 2), with attitude N10W/30SW and contact metamorphism associated to the emplacement of granitic bodies, the third phase is characterized by a weak retrometamorphic cleavage (S 3) with attitude N10E/ 80NW, that evolves local and gradually to strike-slip shear zones. The geological data suggest that this province was formed syn- to post tectonic to the D2 deformational set associated to the end of the collisional event in the Southeastern of the Amazonian Craton.

O Grupo Canastra em sua área-tipo, região de Tapira, sudoeste do estado de Minas Gerais

This work aimed at describing the Neoproterozoic evolution of a Southern Brasília Fold Belt segment, in Tapira area (southwest of Minas Gerais state, Brazil), using detailed geologic mapping. This area, the Canastra Group type-area, has showed great tectonic and stratigraphic complexities unlike the simplicity suggested in previous works. From recognizing the main tectonic discontinuities, it was possible to subdivide the area into some domains. In the west domain, they were individualized in tectonic sheet I, marked by pelitic rocks and pelitic-graphite rocks with psammitic intercalations, and II, pelitic rocks with psammitic and mafic-ultramafic intercalations overlapped by gneisses. In the east domain, a group of three tectonic sheets was defined, in which, in the two lower tectonic sheets, pelitic and pelitic-graphite rocks with psammitic rock intercalations prevailed, which is different in metamorphic conditions. The lower tectonic sheet is marked by mineralogical associations with muscovite + chlorite + quartz ± graphite ± albite, without biotite; however, the superior one is with muscovite + quartz + garnet ± chlorite ± biotite ± chloritoid ± graphite ± albite. In the upper tectonic sheet, pelitic rocks with local contributions of psammitic and ultramafics rocks occur. In the south domain, psammitic rocks basically occur with contributions of pelitics and rudaceous rocks, where the preservation of textures and sedimentary structures is common. Rocks of the several domains are interpreted as part of a passive continental margin basin, located in the western margin of the São Francisco paleocontinent. Thus, the south domain rocks would represent the facies of proximal platform; rocks of the lower and middle tectonic sheets (east domain) and of the tectonic sheet I (west domain) are of facies distal platform; and the ones from the upper tectonic sheet (east domain) and tectonic sheet II (west domain) were acknowledged as deposited in an environment of continental shelf and/or oceanic seafoor.

Transformações metamórficas e química mineral de cromitas dos corpos de Alvorada de Minas - MG

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caracterização estrutural de um segmento da rampa lateral de capitólio, limite norte da Nappe de Passos - MG

Pós-graduação em Geologia Regional - IGCE

Evolução geológica do sudoeste do cráton amazônico região limítrofe Brasil-Bolívia - Mato Grosso

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização estrutural do embasamento do Grupo Araí, na zona externa da faixa Brasília (GO)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caracterização estrutural, metamórfica e geoquímica da zona interna da faixa Brasília, a Sul de Goiânia

Pós-graduação em Geologia Regional - IGCE

Fácies e proveniência de depósitos costeiros da Formação Raizama: evidências do registro Ediacarano-cambriano na faixa Paraguai, região de Nobres, Mato Grosso

Rochas siliciclásticas da Formação Raizama, unidade basal do Grupo Alto Paraguai de idade ediacarana-cambriana (635 – 541 Ma), ocorrem distribuídas descontinuamente ao longo da margem sul do Cráton Amazônico e segmento norte da Faixa Paraguai, centro-oeste do Brasil, estado do Mato Grosso. Estas recobrem discordantemente os depósitos de plataforma carbonática do Grupo Araras, onde foram registrados evidências do evento glacial Marinoano (635 Ma). O Grupo Alto Paraguai representa os estágios finais da colisão entre os blocos Amazônico e Paranapanema que culminaram no fechamento do Oceano Clymene (540-520 Ma). A Formação Raizama com espessura de aproximadamente 570 m é constituída por pelitos, arenitos finos a grossos, e arenitos com cimento dolomítico previamente interpretados como depósitos flúvio-costeiros distribuídos nos membros inferior (270 m) e superior (300 m). O estudo faciológico e estratigráfico desta unidade na região de Nobres, Estado do Mato Grosso, foi focado principalmente na seção aflorante de 600 m no leito do rio Serragem, que inclui a Cachoeira da Serra do Tombador. Foram definidas 17 fácies sedimentares, agrupadas em cinco associações de fácies (AF) representativas de uma sucessão costeira progradante iniciando por depósitos de shoreface inferior, os quais recobrem em conformidade correlativa os depósitos de plataforma carbonática da Formação Serra do Quilombo (Grupo Araras). A AF1 consiste em arenitos com laminação plano-paralela e laminação truncada por onda (microhummocky), individualizada por camadas de pelito laminado interpretadas como depósitos de shoreface inferior. Destaca-se na AF1 a primeira ocorrência de níveis centimétricos bioturbados por Skolithos em depósitos neoproterozoicos – cambrianos na Faixa Paraguai. A AF2 é formada por arenitos com estratificação cruzada swaley e estratificação plano-paralela interpretada como depósitos de shoreface superior. A AF3 é composta por arenitos com estratificações cruzadas tangenciais e acanaladas com recobrimentos de siltito/arenito muito fino representativos de depósitos de canal e barras de submaré. A AF4 é caracterizada por arenitos com estratificações cruzadas tangencial e sigmoidal, laminação plano-paralela a cruzadas de baixo-ângulo, ritmito arenito muito fino/siltito com acamamento flaser e gretas de contração, organizados em ciclos métricos de raseamento ascendente de planície de maré. A AF5 é constituída por arenito com estratificação cruzada acanalada marcada por lags residuais na base da associação, arenito com estratificações plano-paralela e cruzada de baixo-ângulo, interpretados como depósitos fluviais distais de rios entrelaçados, parcialmente retrabalhados por ondas. Grãos detríticos de zircão foram obtidos da AF3 e datados pelo método U-Pb, sendo a idade de 1001±9 Ma interpretada como a idade de máxima deposição da Formação Raizama. Aliado a tal análise, as paleocorrentes NE-SE mostram que estes grãos teriam como áreas fontes principais a Faixa Sunsás, SW do Cráton Amazônico, não sendo descartada contribuições oriundas da parte NW desse Cráton. A idade mesoproterozóica obtida serviu principalmente para desvendar a proveniência da Formação Raizama, enquanto que as datações da base do Grupo Araras, em torno de 627-622 Ma, associada à presença inequívoca do icnogênero Skolithos, tornam esta unidade muito mais próxima do limite com o Cambriano Inferior. Traços fósseis do Proterozoico são caracterizados quase que exclusivamente por traços horizontais, sendo que bioturbações verticais praticamente são ausentes ao longo do Neoproterozoico. Esta inferência vem de encontro com a idade máxima de 541 Ma obtida para a Formação Diamantino, a qual recobre a unidade estudada. Os dados radiométricos aliados com as interpretações paleoambientais, que incluem o registro das primeiras atividades de organismos perfurantes na Faixa Paraguai, abrem perspectivas de entender com maiores detalhes a sequência de eventos que tipificam os estratos do limite Ediacarano-Cambriano do Brasil, ainda pouco conhecidos.

Estratigrafia da faixa de dobramentos Paraguai-Araguaia no centro-norte do Brasil

A Faixa de Dobramentos Paraguai-Araguaia, constituída no Ciclo Brasiliano, estende-se para o norte da Ilha do Bananal, com orientação sub-meridiana. Acima do paralelo 9º30'S ela se faz representar pelo Grupo Baixo Araguaia, uma faixa ofiolítica, alguns corpos graníticos e pela Formação Rio das Barreiras. O Grupo Baixo Araguaia se constitui de três formações, Estrondo, Couto Magalhães e Pequizeiro, esta última de caráter magmático-sedimentar associada à faixa ofiolítica. A faixa ofiolítica é associada à Geossutura Tocantins-Araguaia, que parece se manifestar à superfície através da falha de empurrão entre o Rio Vermelho e Tucuruí, em associação à qual incide fáceis xisto verde glaucofanítica. A evolução da faixa de dobramentos mostra polaridade para oeste dos vários fenômenos, com exceção do magmatismo básico-ultrabásico.

Caracterização petrográfica dos alvos Hidrotermalitos Norte e Sul, Suruca e porção NW da Mina de Chapada - Alto Horizonte, GO

Main occurrence of Cu-Au in Goias Magmatic Arc, the Chapada mine fits into the geological context of the Brasilia Fold Belt, specifically in the Mara Rosa Magmatic Arc. Four targets, named Hidrotermalito Norte and Sul, NW Chapada Mine Portion and Suruca, are situated in this context, which includes ortogneisses and rocks from the Mara Rosa volcanic-sedimentary sequence. All these targets have been studied due to the possibility of presenting a great potential in Cu-Au, as well as the Chapada mine. Hidrotermalitos Norte and Sul targets presents four lithological sequences, which were identified as: quartz-muscovite schist; muscovite quartzites and kyanite quartzites; quartz-biotite-amphibole schist with pyrite and epidote-amphibole-biotite gneisses with muscovite; muscovite-biotite gneisses. They are metamorphosed to amphibolites facies and retrogressive greenschist facies. Sulfetation represented mainly by pyrite. In the NW Chapada Mine Portion, three main lithological groups were identified and classified as biotite gneisses; honblende-quartz-biotite-schist; amphibolites, with the first group metamorphosed in greenschist facies (low grade), and the other two groups metamorphosed in amphibolites facies, with subsequent retrogressive metamorphism in greenschist facies. Sulfetation is represented by chalcopyrite and pyrite. Finally, also three main lithological groups were identified in the Suruca target, classified as garnet-chlorite-epidote-eiotite gneiss; biotite gneiss and chlorite-biotite gneiss with epidote and muscovite; muscovite-quartz schist, all them metamorphised in amphibolites, with retrometamorphism in greenschist facies. Sulfetation represented by pyrite and sphalerite