Geotectônica e evolução crustal das faixas Rio Preto e Riacho do Pontal, estados da Bahia, Pernambuco e Piauí

Exportado OPUSMade available in DSpace on 2019-08-14T07:39:49Z (GMT). No. of bitstreams: 1 tese_fcaxito_2013_volume_unico.pdf: 135400607 bytes, checksum: 1f555eb51f93631227985b7b878aee02 (MD5) Previous issue date: 25As faixas Rio Preto e Riacho do Pontal são parte do extenso sistema orogênico Brasiliano / Pan-Africano do Supercontinente Gondwana Ocidental no Nordeste do Brasil, se estendendo por aproximadamente 600 km na direção SW-NE nas margens noroeste e norte do Cráton do São Francisco. A Faixa Rio Preto é composta pela Formação Formosa (xisto, quartzito, anfibolito), provavelmente depositada em uma bacia retro-arco paleoproterozóica (~1.9 Ga) e, portanto, parte do embasamento da faixa dobrada; e pela Formação Canabravinha (metadiamictito, metagrauvaca, metaturbidito), que representa o preenchimento de uma bacia rift neoproterozóica (900-600 Ma). A deformação brasiliana ocasionou a inversão da bacia intracontinental e gerou uma estrutura complexa em leque assimétrico de dupla vergência, entre 600 e 540 Ma atrás. A Faixa Riacho do Pontal pode ser subdividida em três domínios tectono-estratigráficos, de norte para sul: as zonas Interna (núcleo metamórfico), Central (ofiolítica) e Externa (thrust-and-fold belt). A Zona Interna contém importantes intrusões de augen-gnaisse de idade toniana (Suíte Afeição, 1000-960 Ma) que podem representar uma continuação do Cinturão Cariris Velhos, a nordeste. A Zona Central, cujas características geofísicas são muito similares às de zonas de sutura pré-cambrianas, é caracterizada pelo Complexo Monte Orebe, composto principalmente por metabasaltos e rochas metassedimentares de ambiente marinho profundo. Dados Sm-Nd sugerem uma idade de extrusão dos protólitos dos metabasaltos em torno de 820 Ma. Valores iniciais positivos de Nd(t) = +4.4 e razões 147Sm/144Nd acima da razão condrítica indicam uma fonte de manto empobrecido, o que, conjuntamente à química do tipo T-MORB, semelhante aos ofiolitos relacionados à zonas de subducção, sugere que os metabasaltos representam remanescentes obductados de uma crosta oceânica neoproterozóica. A Zona Externa é caracterizada pelo sistema de nappes Casa Nova, composto por duas unidades, da base para o topo: A Formação Barra Bonita, uma sequência plataformal que representa parte da margem passiva norte do Cráton do São Francisco; e a Formação Mandacaru, uma sequência turbidítica do tipo flysch, depositada em uma bacia de margem ativa há aproximadamente 630 Ma atrás. Toda a faixa dobrada é intrudida por granitóides sin a pós-colisionais de idade Neoproterozóica tardia (~630-540 Ma). A Faixa Riacho do Pontal provavelmente representa um ciclo de placas tectônicas completo no Neoproterozóico tardio, envolvendo a colisão do Cráton do São Francisco com a porção extremo oeste do bloco de Pernambuco Alagoas, a norte. Esta interpretação diverge de visões da Província Borborema como um bloco coerente desde o Paleoproterozóico (parte do Supercontinente Atlântica) sugerindo, ao invés, um ambiente dinâmico onde múltiplas placas interagiram para formar esta porção do Supercontinente Gondwana Ocidental.The Rio Preto and Riacho do Pontal fold belts are part of the extensive Brasiliano / Pan- African branch of orogens of West Gondwana in Northeast Brazil, extending up to 600 km in a SWNE trend within the northwest and north São Francisco Craton margins. The Rio Preto Fold Belt is composed by Formosa Formation (schist, quartzite, amphibolite), probably deposited in a paleoproterozoic (~1.9 Ga) back-arc basin and thus part of the basement to the fold belt; and the Canabravinha Formation (metadiamictite, metawacke, metaturbidite), probably deposited in a Neoproterozoic (900-600 Ma) rift basin. Neoproterozoic deformation originated a complex assymetrical doubly-vergent fan structure, between 600 and 540 Ma ago. The Rio Preto Fold Belt probably represents the inversion of an intracontinental basin, as orogenic or oceanic rocks have not yet been identified within its outcropping area. The Riacho do Pontal Fold Belt can be subdivided in three tectono-stratigraphic domains, from north to south: The Internal (metamorphic core), Central (ophiolitic) and External (thrust-and-fold belt) zones. The Internal Zone contains important Tonianaged (1000-960 Ma) augen-gneiss intrusions (Afeição Suite) which might represent a continuation of the Cariris Velhos Orogen further northeast. The Central Zone, whose geophysical characteristics are very similar to those of Precambrian suture zones, is characterized by the Monte Orebe Complex, composed mainly by metabasalts and deep-sea metasedimentary rocks. Sm-Nd whole rock data suggest extrusion of the metabasalt protholits at around 820 Ma. Initial Nd(t) = +4.4 and 147Sm/144Nd values above the chondrite ratio indicates a depleted mantle source, which together with a T-MORB, subduction-related ophiolite geochemistry, suggest that the metabasalts represent obducted remnants of a Neoproterozoic oceanic crust. The External Zone is characterized by the Casa Nova nappe system, which is composed by two units, from the bottom up: The Barra Bonita Formation, representing a platformal sequence which is broadly coeval to the cratonic cover of the Una Group and thus represent part of the northern São Francisco paleocontinent passive margin; and the Mandacaru Formation, which is a turbiditic, flysch-like unit, deposited in an active margin basin with sources toward north, at around 630 Ma ago. The whole belt is intruded by extensive syn to post- collisional granitoids of late Neoproterozoic to Cambrian age (~630-530 Ma). The Riacho do Pontal Fold Belt probably represents a complete plate tectonics cycle in the late Neoproterozoic, involving the collision of the São Francisco Craton with the western edge of the Pernambuco Alagoas block further north. This interpretation challenges a view of the Borborema Province as a coherent block since the Paleoproterozoic (part of the Atlantica Supercontinent); suggesting, instead, a dynamic setting where multiple plates interacted to form this portion of West Gondwana

Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at ?gua Vermelha dam, Tri?ngulo Mineiro, Brazil : implications for the magmatic evolution of the Paran??Etendeka Province.

The Serra Geral Formation belongs to the Paran?-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the ?gua Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups?central flow, basal flow, main ring dyke and lava flow?with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of ?gua Vermelha are important to comprehend the evolution of the PEMP

Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at Água Vermelha dam, Triângulo Mineiro, Brazil: implications for the magmatic evolution of the Paraná-Etendeka Province

ABSTRACT: The Serra Geral Formation belongs to the Paraná-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the Água Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups-central flow, basal flow, main ring dyke and lava flow-with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of Água Vermelha are important to comprehend the evolution of the PEMP

Idade máxima de sedimentação e proveniência do Complexo Jequitinhonha na área-tipo (Orógeno Araçuaí) : primeiros dados U-Pb (LA-ICP-MS) de grãos detríticos de zircão.

O Complexo Jequitinhonha, situado no nordeste de Minas Gerais, é uma das unidades metassedimentares mais extensas do Orógeno Araçuaí. Na área-tipo, situada na região de Jequitinhonha -Almenara, este complexo consiste de paragnaisse peraluminoso (kinzigítico) migmatizado, com intercalações de quartzito, grafita gnaisse e rocha calcissilicática. Os dados isotópicos U-Pb (LA-ICP-MS) de 80 grãos detríticos de zircão de uma amostra de quartzito, coletada em corte da BR-367 cerca de 12 km a SW de Almenara, permitem identificar seis principais intervalos de idades, cujas médias das modas sugerem as seguintes fontes de sedimentos: o embasamento São Francisco-Congo (2541 ± 8 Ma e 2044 ± 6 Ma), o sistema Espinhaço-Chapada Diamantina (1819 ± 6 Ma, 1487 ± 5 Ma e 1219 ± 3 Ma) e o sistema de rifteamento Noqui-Zadiniano-Mayumbiano-Salto da Divisa (956 ± 4 Ma). A idade máxima de sedimentação em 898 ± 8 Ma é dada pelo zircão mais novo. Os espectros de idades desta amostra do Complexo Jequitinhonha e de rochas do Grupo Macaúbas são muito similares, indicando correlação entre estas unidades. Contudo, no Complexo Jequitinhonha inexiste evidência de glaciação. Assim, o Complexo Jequitinhonha na área-tipo é interpretado como depósito de margem passiva da bacia precursora do Orógeno Araçuaí, mais novo que a glaciação Macaúbas e, portanto, equivalente às formações Chapada Acauã Superior e Ribeirão da Folha.The Jequitinhonha Complex is one of the most extensive metasedimentary units of the Araçuaí Orogen. In the type-area, located in the Jequitinhonha-Almenara region, this complex includes migmatized peraluminous (kinzigitic) paragneiss with intercalations of quartzite, graphite gneiss and calcsilicate rock. U-Pb (LA-ICP-MS) data from 80 detrital zircon grains extracted from a quartzite sample, collected in a BR-367 road cut around 12 km SW from Almenara, yielded six main age intervals, which mode mean values suggest the following sediment sources: the São Francisco-Congo basement (2541 ± 8 Ma and 2044 ± 6 Ma), the Espinhaço-Chapada Diamantina system (1819 ± 6 Ma, 1487 ± 5 Ma and 1219 ± 3 Ma), and the Noqui-Zadinian-Mayumbian-Salto da Divisa rift system (956 ± 4 Ma). The maximum sedimentation age of 898 ± 8 Ma is constrained by the youngest zircon grain. Spectra of detrital zircon ages for this sample of the Jequitinhonha Complex and rocks of the Macaúbas Group are very similar and suggest a correlation between these units. However, this complex shows no evidence of glaciation. Therefore, the Jequitinhonha Complex in its type-area is interpreted as a passive margin deposit of the precursor basin of the Araçuaí Orogen, younger than the Macaúbas glaciation and, thus, equivalent of the Upper Chapada Acauã and Ribeirão da Folha formations

Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at Água Vermelha dam, Triângulo Mineiro, Brazil: implications for the magmatic evolution of the Paraná-Etendeka Province

<div><p>ABSTRACT: The Serra Geral Formation belongs to the Paraná-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the Água Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups-central flow, basal flow, main ring dyke and lava flow-with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of Água Vermelha are important to comprehend the evolution of the PEMP.</p></div

Neoproterozoic magmatic arc volcanism in the Borborema Province, NE Brazil : possible flare-ups and lulls and implications for western Gondwana assembly.

New zircon U-Pb (SHRIMP and LA-ICPMS), elemental and Nd-Sr geochemistry data on rhyolitic metavolcanic and metavolcaniclastic rocks of NE Brazil characterize widespread arc-related phenomena during the Neoproterozoic, related to the Concei??o-type or Stage I plutonic rocks. U-Pb zircon dating pinpoint the main phase of magmatic activity at ca. 635-600 Ma in the 700-km long sigmoidal Pianc?-Alto Br?gida domain, but other important flareups might have taken place at ca. 670-690, 730-760, 810-820 and 860-880 Ma. A comprehensive compilation of detrital zircon data from metavolcanosedimentary successions of the entire Borborema Province (n=5532) confirms the occurrence of a quasi-continuum Neoproterozoic spectra punctuated by peaks at those same age intervals separated by minor lulls. Low Th/U rims of zircon crystals dated at ca. 577 Ma provide an estimate of the age of regional transpressional metamorphism. Samples of all age ranges are mostly calc-alkaline, magnesian and peraluminous, with moderately to highly fractionated LREE enrichment, negative Nb-Ta anomalies akin to convergent settings, and plot mainly within the volcanic arc field in tectonic discrimination diagrams. Nd-Sr isotope systematics indicate the involvement of juvenile Neoproterozoic melts from the mantle wedge, which upon mixing with Archean-Paleoproterozoic basement and contamination with the host metasedimentary rocks yield Mesoproterozoic TDM mainly at 1.14-1.44 Ga, near-chondritic ?Nd(t) and 87Sr/86Sri 0.703-0.710.We put forward a model involving a major continental back-arc zone related to the development of the Concei??o magmatic arc, akin to the modern-day Taupo volcanic zone of New Zealand, crosscutting NE Brazil and presumably continuing through the schist belts of Nigeria and Cameroon. The main magmatic flare ups might have been induced by extra-arc phenomena, such as collision of the West African paleocontinent with the northwestern Borborema edge due to closure of the exterior Goi?s-Pharusian Ocean, force-speeding subduction in the interior V-shaped oceanic basins that constituted the Transnordestino-Central African Ocean and generating clockwise windshield-wiper-like rotation of the blocks back towards the S?o Francisco-Congo paleocontinent in a complete Wilson Cycle