Navegando por Assunto "Petrografia"

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Batólito Guaporeí: uma extensão do Complexo Granitoide Pensamiento em Mato Grosso, SW do Cráton Amazônico
(2013-03) NALON, Patrícia Alves; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; MACAMBIRA, Moacir José Buenano
The Guaporeí Batholith is located in the Vila Bela da Santíssima Trindade region, at Mato Grosso State (Brazil), and crops out over 240 km2 along the NW direction. It is situated in the Paraguá Terrane, included in the Rondonian-San Ignacio Province, in the southwestern portion of the Amazonian Craton. The batholith is made up of monzogranite, with subordinate granodiorite, quartz monzonite and syenogranite, shows coarse porphyritic/porphyroclastic texture, is metamorphosed in the greenschist facies and mylonitized along shear zones. The biotite is the main primary mafic mineral, sometimes associated with amphibole. Geochemical data indicated high-potassium calc-alkaline and metaluminous to peraluminous character, probably generated in continental arc environment, and evolved by fractional crystallization associated to crustal assimilation. Two stages of deformation related to the evolution of San Ignacio compressional orogeny were identified and are characterized by stretching and lineation, and development of S1 and S2 foliations. Dating by single zircon Pb-evaporation method yields a crystallization age of 1,314 ± 3 Ma, whereas Sm-Nd whole rock isotope data indicate a TDM model age of ca. 1.7 Ga and a negative value for εNd (t = 1,3) of -14, suggesting crustal contribution in the magma genesis. The obtained data indicate similarities between these rocks and those of the Pensamiento Granitoid Complex, in the Bolivian counterpart, and put in evidence that the Guaporeí Batholith is an extension of this complex.
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Caracterização geológica, petrográfica e geoquímica do Trondhjemito Mogno e Tonalito Mariazinha, Terreno Granito-Greenstone mesoarqueano de Rio Maria, SE do Pará
(2010-06) GUIMARÃES, Fabriciana Vieira; DALL'AGNOL, Roberto; ALMEIDA, José de Arimatéia Costa de; OLIVEIRA, Marcelo Augusto de
The Mogno Trondhjemite is one of the largest TTG units of the Rio Maria Granite-Greenstone Terrane (RMGGT). It was considered as representative of a second generation of Archean TTG in that terrane. However, field, petrographical, geochemical, and geochronological studies demonstrate the existence of two distinct TTG units in its main area of occurrence. For the dominant TTG unit, showing NW-SE to EW foliation and distributed in the eastern and western domains of the mapped area, the term Mogno Trondhjemite was maintained. The new TTG unit, which occurs in the center-western domain and displays a NE-SW to NS dominant trend, is named as Mariazinha Tonalite. Hence, the original area of occurrence of the Mogno Trondhjemite was significantly reduced. Moreover, Pb-Pb zircon ages indicate that the Mogno Trondhjemite and the Mariazinha Tonalite are neither coeval, nor related to the second generation of TTGs of the RMGGT. The two TTG studied units are composed of epidote-biotite tonalites and trondhjemites of the high Al2O3 type, with geochemical characteristics similar to those of the typical Archean TTG granitoids. Compared with the Archean TTG units of the Xinguara region, the Mogno Trondhjemite geochemical characteristics are transitional between those of the Caracol Tonalitic Complex and the Água Fria Trondhjemite, while those of the Mariazinha Tonalite approaches those of the Caracol Tonalitic Complex. The studies undertaken in the Mogno Trondhjemite and associated Archean granitoids demonstrated that the TTG series of the RMGGT are more diversified and complex than previously admitted. The domain of the second Archean generation of TTG of the RMGGT was drastically reduced and a new Archean TTG association, the Mariazinha Tonalite, was identified and characterized.
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Caracterização geológica, petrográfica, geoquímica e geocronológica do magmatismo granítico da região de Porto Nacional-TO
(Universidade Federal do Pará, 2003-02-28) CHAVES, César Lisboa; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
In the Palmas-Porto Nacional region, Tocantins state, a series of granitic bodies has been assigned to two distinct magmatics events: a) Paleoproterozoic Granites (Areias, Carmo, Itália and Ipueiras plutons); b) Neoproterozoic Granites (Lajeado, Aroeira, Matança and Palmas plutons). Cartographic, petrographic, lithochemical and geochronological studies revealed the main characteristic of these granitic bodies and allowed to improve the knowledge of the granitic magmatism of this region. The Paleoproterozoic granites constitute large bodies affected by small strike-slip zones. Petrographically they are represented by sienogranite, monzogranite and quartz syenite, with different amounts of amphibole and biotite. The geochemical signature of the Paleoproterozoic granites are similar. The show a subalcaline character, and are peraluminous to metaluminous. They are rich in REE and, generally, more fractioned in LREE, with negative Eu anomaly and may be classified as A-type granites. Single zircon Pb-evaporation dating of Areias, Ipueiras and Itália granites gave ages of 2086  5 Ma, 2073  2 Ma and 2078  4 Ma, respectively, interpreted as age of emplacement of these plutons. Sm-Nd TDM model ages between 2.19 Ga and 2.15 Ga suggest that these granites were formed by partial melting of Paleoproterozoic juvenile crust. The Nd(2,08Ga) values between +2.26 and +2.89 indicate the mantelic contribution for the formation of these plutons. The Neoproterozoic granites are petrographically classified as sienogranite, monzogranite and quartz sienite with different amounts of ortopyroxene, amphibole and biotite, In general, they may be called charnockites. The geochemical date revealed similarities among the Neoproterozoic granites. They show subalkaline nature and have metaluminous to peraluminous character. These granites are rich in REE and are more fractioned in HREE than LREE. In the geochemical diagrams they plot in the field of the A-type granites. The Sm-Nd isotopics studies for Neoproterozoic granites revealed TDM ages between 2.1 Ga and 1.71 Ga and the Nd(0,55Ga) values between –13.34 and –9.77 that are interpreted as evidence of strong crustal contribution, but probably with some mixtures of younger of sources. This study corroborated the presence of two main events of granite geration in the Porto National-Palmas region. The older is represented by the Paleoproterozoic Carmo, Areias, Ipueiras and Italia granites, with age around 2.08 Ga. The younger granitogenesis is represented by Lajeado, Palmas, Matança and Aroeira bodies emplaced in the Neoproterozoic at 0.55 Ga.
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Estudo paleontológico do limite oligoceno/mioceno nas formações Ilha de Santana e Pirabas nas bacias Pará-Maranhão e Barreirinhas na plataforma equatorial noroeste do Brasil.
(Universidade Federal do Pará, 2023-12-14) GUIMARÃES, Beatriz Teixeira; AGUILERA SOCORRO, Orangel Antonio; http://lattes.cnpq.br/5854051483674293; https://orcid.org/0000-0003-4418-8351
Sedimentary carbonate outcrops of the Pirabas Formation at the Bragantina Platform in North Brazil represent the exposed portion of the entire carbonate succession in the marine equatorial platform from the subsurface Ilha de Santana Formation (Cretaceous/Maastrichtian-Miocene/Aquitanian) in the Pará-Maranhão Basin and from the Formation Pirabas (Miocene/Aquitanian-Serravallian) in the Barreirinhas Basin, both from the Humberto de Campos Group. The transgressive deposit, flooding, and advance of the carbonate platform were investigated through the study of outcrops of the Pirabas Formation (type locality in the Ilha de Fortaleza, Pará state) and the analogous carbonate of the upper section of the Ilha de Santana Formation of the well-log 1- MAS-16-MA (510 to 660 meters below the seabed). The stratigraphic analyses were based on petrography, microCT, microfossil assemblages (foraminifers, ostracods, and bryozoans) and index species (Amphistegina, Archaias, Pyrgo, Quinqueloculina, Pirabasoporella, Nellia, Skylonia, and Alpheus), and biofacies approach. The boundary between the Ilha de Santana Formation (Aquitanian/Burdigalian at 510–660 m section of 1-MAS-16-MA) and the Pirabas Formation (Burdigalian/Serravallian at the Ilha de Fortaleza outcrop) suggests that shallow-water sedimentary facies are similar to those deposited in the marginal basins and marks the start of siliciclastic supplies to the inner platform and the reduction of coralline algal carbonate factories.
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Estudo petrográfico e geoquímico dos ironstones da base da Formação Pimenteiras, Borda Oeste da Bacia do Parnaíba, Tocantins
(2012-06) AMARO, Gabriel de Jesus Lavareda; VILLAS, Raimundo Netuno Nobre; KOTSCHOUBEY, Basile
Ironstones that occur at the base of the Devonian Pimenteiras Formation (northwestern border of the Parnaíba basin) were investigated along the Xambioá-Vanderlândia and Colinas do Tocantins-Couto Magalhães sections. The ironstones consist of discontinuous decimeter-thick layers intercalated in sandstones and shales that underlie rocks of the Neoproterozoic Araguaia belt. The Xambioá-Vanderlândia ironstones are texturally and chemically quite distinct from those of the Colinas do Tocantins-Couto Magalhães area. Besides the presence of oolites, the former shows smaller amounts of terrigenous material (especially quartz) and higher iron oxide-hydroxides proportions. They also are more enriched in V, Sr, Zr and ΣREE, and poorer in Al2O3 and Rb. The North American Shale Composite (NASC) normalized REE distribution pattern is also different, especially concerning the IREEN values, which, being higher in the oolithic ironstones, display convex curves and, being lower in the non-oolithic ironstones, display concave ones. In the field, spatial relationships could not be defined between both ironstone types. It is then suggested that they represent different lithological facies of the same iron formation. Probably, the deposition of the non-oolithic facies occurred in deeper and quieter waters away from the continental border, where larger amounts of detrital sediments were discharged, whereas the deposition of the oolithic facies took place in shallower and more agitated waters, with less supply of terrigenous material. Iron was largely derived from the erosion of continental areas where reduced environments favored its mobilization and transport by rivers as suspended particles, colloids, and organic complexes.
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Evolução dos fluidos mineralizantes e modelo genético dos veios de quartzo auríferos em zona de cisalhamento do depósito Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-12) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias; JAVIER RIOS, Francisco
The Ouro Roxo gold deposit, located near Jacareacanga, Tapajós Gold Province, southwestern Para, Brazil, comprises a hydrothermal system of sulfide quartz veins that was hosted by the calc-alkaline mylonite granitoid Tropas Intrusive Suite of Paleoproterozoic age and controlled by the N-S trending ductile-brittle oblique Ouro Roxo-Canta Galo, crosscutting the granitoid Tropas. Three kinds of fluids were identified as sources of mineralization in the Ouro Roxo deposit: 1) an aqueous fluid within the H2O-NaCl-MgCl2-FeCl2 system, with low-to-middle salinity and homogenization temperature (Th) = 180-280°C; 2) Cu and Bi-bearing H2O-NaCl-CaCl2 brines, with Th = 270-400°C, genetically related to a magmatic event coeval to shearing, which underwent dilution by mixing with meteoric water; 3) gold bearing middle-salinity aquocarbonic fluid, with Th = 230-430°C, which was interpreted as ore fluid related to shearing. The T-P conditions of ore formation, estimated by chlorite geothermometer and fluid inclusion isochors, range from 315 to 388°C and 2,0 to 4,1kb. The two main mechanisms for gold deposition in transtensional sites of the shear zone were: 1) Mixing of aquocarbonic fluid and magmatic brines induced an increasing of fO2 and decrease of pH; 2) interaction between fluids and feldspars and ferromagnesian minerals of the hoster granitoid which reduced fO2 and fS2 during hydrolysis and sulfidation reactions, with precipitation of iron sulfides together with gold. The orogenic environment, the veining style, the structural control by shearing, the hydrothermal alteration (propylitic+philic+carbonatization), the metallic association (Au+Cu+Bi), the association of aquocarbonic ore fluid with magmatic brines in ore deposition, are all consistent with an orogenic model for genesis of the Ouro Roxo deposit with magmatic participation.
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Field and petrographic data of 1.90 to 1.88 Ga I- and A-type granitoids from the central region of the Amazonian Craton, NE Amazonas State, Brazil
(2012-12) VALERIO, Cristóvão da Silva; MACAMBIRA, Moacir José Buenano; SOUZA, Valmir da Silva
The SW Presidente Figueiredo district, which is located in the northeastern Amazonas State of the central Amazonian Craton, Brazil, consists of 1890 to 1898 Ma I-type granitoids (Terra Preta Granite, Água Branca Suite), A-type hornblende-bearing syenogranites (Canoas Syenogranite, Mapuera Suite), felsic to intermediate volcanic rocks (Iricoumé Group), and 1883 to 1889 Ma rapakivi granites (São Gabriel Granite, Mapuera Suite) and related rocks (quartz-gabbro-anorthosite and diorite), in addition to Castanhal quartz-monzonite, mylonites, and hornfels. The quartz-diorite facies of Terra Preta Granite were formed by mingling processes between a synplutonic quartz-gabbro dike and a hornblende granodiorite. Partially assimilated globules of Canoas hornblende-bearing syenogranite and their clear contacts with Terra Preta hornblende granodiorite suggest that Canoas Syenogranite is slightly younger than Terra Preta Granite. Canoas Syenogranite xenoliths inside São Gabriel Granite show that the granite is younger than the Canoas Syenogranite. New geologic and petrographic evidence improve the petrological understanding of these rocks and suggest that, in addition to fractional crystallization, assimilation and magma mingling played a role, at least at the local scale, in the evolution and compositional variation of the plutons. Such evidence is found in Terra Preta Granite mingled quartz-diorite, felsic material associated with the Canoas Syenogranite and in the intermediate microgranular enclaves, which exhibit primary biotite in hornblende-bearing rocks, plagioclase dissolution, corrosion of feldspars rims, alkali feldspar mantles, second apatite generation, and high xenocrystal contents in intermediate enclaves formed from the fragmentation of mafic intrusions. Petrographic analyses show that a deformational event recorded in the western part of the study area (with progressive deformation from E to W) is dated between the 1.90 Ga postcollisional magmatism and the intrusions of the São Gabriel Granite and related mafic/intermediate rocks (intra-plate). However, it is extremely necessary to obtain absolute ages for this metamorphic event.
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Geologia, petrografia e geocronologia das rochas do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-03) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias
The Ouro Roxo gold deposit lies near the city of Jacareacanga, Tapajós Gold Province, southwestern of Pará, Brazil. The Ouro Roxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonite granitoid Tropas Intrusive Suit of Paleoproterozoic age and controlled by the N-S trending Ouro Roxo-Canta Galo shear zone (OCSZ). The host granitoids are oxidized calc-alkaline granodiorite and tonalite of magmatic arc filiation. The OCSZ is a sinistral oblique ductile-brittle shear, which belongs to the third deformation event of the Tapajós Province and has turned the granitoids into protomylonites, mylonites and breccias. The NNE-SSW mylonitic foliation dipping to ESE and stretch lineation in quartz grains indicate the tectonic movement to NW. Mineralized quartz veins and pipes are hosted by mylonites and breccias and surrounded by hydrothermal alteration halos. Besides silicification and sulfidation, concentrated in the ore bodies, three types of wall-rock alteration occur: propilitization (chlorite + phengite + carbonate); phylic alteration (phengite + quartz + carbonate + pyrite); carbonatization. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes. The isotopic Pb-Pb data do not support a genetic relationship between the gold deposit and the Tropas granitoids, being the deposit coeval to Maloquinha granite. The orogenic environment, the veining style, the structural control, the hydrothermal alteration and the metallic association (Au + Cu + Bi), are all consistent with a mesozona-epizona orogenic model for the genisis of the Ouro Roxo deposit.
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Geologia, petrografia e geocronologia do Plúton Alcalino Brejinho - nordeste do Piauí / noroeste do Ceará
(Universidade Federal do Pará, 2001-06-25) BARBOSA, RITA DE CÁSSIA DE OLIVEIRA; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502; https://orcid.org/0000-0003-1877-9756
The present work reports geological, petrographic and geochronological data of the alkaline pluton Nefelina Sienito Brejinho. The Nefelina Sienito Brejinho is inserted in the northwest portion of the Borborema Province, geographically located on the border of the states of Piauí and Ceará, approximately 60 km southeast of the city of Parnaíba. The pluton has approximate dimensions of 16 km long and 8 km wide and has a roughly triangular shape, elongated in the NNE direction. It is a typically igneous body, where its intrusive character was evidenced in gneisses and amphibolites of the Granja Complex, with cooling edges, xenoliths and small zones of hornfels. In general, the rocks along the plutonic body present magmatic feeding structures defining a preferential orientation in the NNE-SSW direction marked by tubular alkaline feldspar crystals, prismatic pyroxenes, lamellar biotites and, in some cases, this foliation is also evidenced by amphiboles and titanite. The petrographic and field studies allowed identifying three petrographic facies internally in the pluton: Pyroxene Microclimate Syenite, Pyrogen Nepheline Syenite and Leucosienites. The first two are dominant, and the other has restricted occurrences. Mineralogically the pluton presents a variation, qualitatively and quantitatively. Rocks in general consist essentially of microclimate, nepheline and aegirine-augite as essential minerals. In smaller percentages occur biotite, amphibole (arfvedsonite and riebeckite) and titanite. Accessory to apatite, opaque and fluorite. With regard to textural aspects, trachytoid textures are predominant in the pluton, defined by crystals of alkaline feldspar, pyroxene, biotite, titanite and amphibole. Subordinately, simplectitic intergrowth textures between alkaline and nepheline feldspar are present. This textural aspect suggests subsolvus crystallization for Nefelina Sienito Brejinho. The geochronological studies, carried out using the Rb-Sr methodology in eight rock samples, provided the Nefelina Sienito Brejinho with an age of 545 ± 11 Ma, with an initial ratio of 0.7173 ± 0.0002 and MSWD of 1.32. Based on this age, interpreted as the minimum crystallization age, it is suggested that the syenitic pluton was placed in the Lower Cambrian, during the distensive tectonics that occurred in this portion of NE Brazil. This tectonic was marked by the implementation of the Ubajara-Jaibaras System and by plutonism and volcanism, with an alkaline tendency, such as the Meruoca, Mucambo, Pajé, Anil, Morrinhos and São Paulo granites, among others; and the alkaline volcanism of the Parapuí Suite.
Desconhecido
Geologia, petrografia e geoquímica da associação tonalitotrondhjemito-granodiorito (TTG) do extremo leste do subdomínio de transição, Província Carajás
(Universidade Federal do Pará, 2013-07-31) SANTOS, Patrick Araujo dos; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The eastern border of the Transition Subdomain of the Carajás Province is constituteddominantly of Archean tonalite-trondhjemite-granodiorite (TTG). Deformed monzogranites, similar to the Planalto granite suite, and metagabbros inserted in association mafic-enderbitic also occur. Paleoproterozoic isotropic granites and mafic dykes devoid of significant deformation crosscut the Archean lithologies. The TTGs are exposed as blocks or as flat outcrops in areas of low relief and commonly include quartz-diorite enclaves. The TTG rocks display gray colour and are generally medium-grained, showing compositional banding or, sometimes, homogeneous aspect. They show commonly a NW-SW to E-W trending foliation with vertical to subvertical dips and were submitted to NE-SW stress. Locally, it was identified a NE-SW foliation transposed to E-W along shear zones. In some instances, they exhibit mylonitic to protomilonitics features, registered in the oval form of plagioclase porphyroclasts or boudinated leucogranitics veins. Two petrographic varieties are recognized for this association: biotite-trondjhemite and subordinate biotite-granodiorites, both have similar mineralogical and textural aspects and are characterized by a poorly preserved igneous texture, partially overwritten by an intense recrystallization. EDS analyses revealed that the plagioclase is a calcic oligoclase (An27-19), with Or ranging from 0.6 - 2.3%. The biotites are ferromagnesian, with dominance of Fe over Mg (Fe / [Fe + Mg] ranging from 0.54 to 0.59) and the analyzed epidote presents pistacite contents ranging from 23 to 27.6 % and plot mostly in the range of magmatic epidotes. The trondhjemite shows all typical characteristics of Archean TTG suites. They have high La/Yb and Sr/Y ratios, suggesting they were derived from the partial melting of garnet amphibolite sources at high pressures (ca. 1.5 GPa) or, at least, that their magmatic evolution was controlled by the fractionation of garnet and possibly amphibole, without significant influence of plagioclase. The studied TTGs show similarities with Mariazinha tonalite and Mogno trondjemite, of the Rio Maria Domain, Colorado trondhjemite and, in at a lesser degree, to the Rio Verde trondhjemite, of the Carajás Domain. The granodiorites display a calc-alkaline signature and shows LILE enrichment, specifically K²O, Rb and Ba, when compared to the trondhjemites, but still preserving some geochemical features of the TTG. The geochemical data indicate that the trondhjemite and granodiorite are not related by fractional crystallization. An origin of the granodiorite by partial melting of the TTG rocks is also discarded. The granodiorite could, however, result of contamination of TTG magmas by lithosphere metasomatism or assimilation of sediments from subducted oceanic crust along trondhjemite liquid genesis. In the eastern portion of the mapped area, it was identified a small, E-W trending granite stock clearly controlled by shear zones. The rocks have mylonitic textures, characterized by ovoid-shaped feldspar porphyroclasts, wrapped by recrystallized quartz and mica. These granitic rocks have geochemical signatures of reduced A-type granites and are similar to the Planalto granite suite. Boulders of mafic rocks crop out locally in the northern portion of the area. These rocks show a dominant granoblastic texture, and are mainly composed of amphibole and plagioclase, with subordinate biotite and quartz. In the northern part of the mapped area, it was identified a body of isotropic granite without significant deformation and showing locally rapakivi textures. This granitic pluton was correlated to the Paleoproterozoic A-type granites, represented in the Carajás Domain by the Serra dos Carajás suite and Rio Branco Granite. These granites were not studied in detail. The geological and geochemical aspects shown by the Archean granitoids identified in the eastern part of the Transition Subdomain implies in the existence of significant TTG rocks in the Transition Subdomain. This reinforces the hypothesis that the Transition Subdomain could represent an extension of the Rio Maria Domain, but affected by crustal reworking events in the Neoarchean.
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Geologia, petrografia e geoquímica das associações leucograníticas e TTG arqueanos da área de Nova Canadá (PA) Domínio Carajás
(Universidade Federal do Pará, 2014-02-25) SANTOS, Pablo José Leite dos; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506
The geological mapping carried out in the Nova Canada and Velha Canada villages, south portion of the Carajas Domain, ally to the petrographic and geochemical data allowed to the characterization of new geological units before inserted in the Xingu Complex geological context. In abundance order they are: (i) Nova Canada Leucogranodiorite composed predominantly by leucogranodiorite rocks that are more enriched in Al2O3, CaO, Na2O, Ba, Sr and in the Sr/Y ratio. They show strong geochemical affinities with Guarantã Suites from the Rio Maria Domain, which are also correlated to Transitional TTGs from Yilgarn Craton. Their REE pattern is slightly fractionated with low (La/Yb)N ratios with Eu negative anomalies absent or discrete; (ii) Velha Canadá Leucogranite comprised essentially by leucogranitic rocks that show higher contents of SiO2, Fe2O3, TiO2, K2O, Rb, HFSE (Zr, Y e Nb), and K2O/Na2O, FeOt/(FeOt+MgO), Ba/Sr e Rb/Sr ratios. The Velha Canada area rocks are characterized by two distinct patterns REE of: (a) moderate to low (La/Yb)N ratios with accentuated Eu negative anomalies, and (b) high to moderate (La/Yb)N ratios with discrete Eu negative anomalies. A concave HREE pattern is observed. In several aspects, the Velha Canada granite show similarities with K-Leucogranites like Xinguara and Mata Surrão granites from Rio Maria Domain, and more discretely with low-Ca granites from Yilgarn Craton. To origin of Nova Canadá Leucogranodiorite rocks is admitted fractional crystallization by sanukitoid liquids, following by mixing with trondhjemitic magmas, while for those high-K rocks is assumed partial melting of metatonalites rocks related to TTG Suites on different crustal levels, for give rise to these liquids; and (iii) Trondhjemitic associations with high-Al and low-K calc-alkaline TTG series affinities. Two varieties were distinguished: (a) biotite-trondhjemite with deformational features like compositional banding, folds and evidence of migmatization, suggesting the presence at least two compressional events during the sin- and post magmamtic stages; and (b) (muscovite) biotite-trondhjemite that differs from the previous one by the presence of muscovite, plagioclase saussuritization, medium evengrained texture and discrete deformation features with development of a low-angle foliation with E-W direction. The restrict occurrence of the first one, ally with intense deformation and eventual anatexie processes that affected these rocks, can indicate a crustal rework linked to generation of the leucogranites described in the Nova Canadá area. The trondhjemites of the southern part of area are more enriched in Fe2O3, MgO, TiO2, CaO, Zr, Rb, an in the Rb/Sr ratio in relation to those of the northern part. The arrangement of trends defined by the set of analyzed samples, suggests that theses varieties are not cogenitc or comagmatic. These rocks also show fractionated REE patterns, with variations in contents of the heavy REE and Strong light REE enrichment, besides the absence of the Eu and Sr anomalies, and low contents of Yb and Y. Such aspects are tipically attributed to magmas generated from partial melting of a mafic source at different depths, with increasing of the garnet influence in the residue, as well as the lack of plagioclase in both residual and fractionating phases. Geochemical affinities between the rocks studied with those of the mesoarchean Rio Maria domain, suggest the extension of Rio Maria Domain to north until the Nova Canadá area, while that the leuocogranodiorites of the Velha Canadá area, that are younger and generated in the neoarchean, discard the hypothesis to associate the generation of these rocks to the same tectonic-magmatic events that acted in Rio Maria.
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Geologia, petrografia e geoquímica das rochas vulcânicas Uatumã na área sul de São Félix do Xingu (PA), Província Carajás
(2013-03) FERREIRA, Ana Tayla Rodrigues; LAMARÃO, Cláudio Nery
The volcanic rocks southern São Félix do Xingu, Pará state, north Brazil, are geologically inserted in the geochronologic Amazonia Central province, southeastern Amazonian craton. These rocks are dominantly related to the Sobreiro Formation, and to the Santa Rosa Formation, both belonging to the Paleoproterozoic Uatumã group. Three facies of the Sobreiro Formation had been identified in this work: subaerial lava flow of subalkaline facies; subaerial lava flow of calc-alkaline to shoshonitic facies; subaerial volcaniclastic facies. The samples of the Santa Rosa Formation are subaerial lava flow. The Sobreiro Formation consists of basaltic andesite, andesite, traquiandesite, traquite, crystal tuffs, lapili-tuffs and polymictic breccias. The lithotypes of the Santa Rosa Formation are rhyolites. Rocks of the Sobreiro Formation have contents of SiO2 between 52.14 and 69.21% (wt%) and K2O/Na2O ratios between 0.16 and 1.62. The Santa Rosa Formation form an evolved series with SiO2 contents between 72.27 and 77.14% (wt%) and K2O/Na2O ratios between 1.50 and 2.12. The Sobreiro Formation is mainly calc-alkaline, weakly transitional calc-alkaline to shoshonitic, has metaluminous to weakly peraluminous composition and tectonic signature of volcanic arc environment. The Santa Rosa Formation has peraluminous to weakly metaluminous composition and A-type signature with intraplate tectonic affinity. The volcanic rocks of the southern area have perfect correlation petrographic, geochemical and tectonic volcanites with the area west/southwest of São Félix do Xingu.
Acesso aberto (Open Access)
Geologia, petrografia e geoquímica dos diques da região de Rio Maria, SE-PA
(Universidade Federal do Pará, 1996-09-09) SILVA JÚNIOR, RENATO OLIVEIRA DA; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
In the region of Rio Maria, SE of Pará, several dykes were mapped, mainly intrusive in the Granodiorite Rio Maria (GdRM) and, subordinately, in the anorogenic granite Musa (GM). Forming small elongated ridges that stand out in the morphology with a positive relief, arranged mainly according to NW-SE and E-W trends and, subordinately, N-NE. The maximum width of these bodies is 30 m, and they have an outcropping length of 1,500 to 2,000 m, reaching 3,000 m. Five groups of dykes were identified petrographically: diabases, diorites, quartz-diorites, dacites and rhyolites. The transverse and longitudinal profiles in the direction of these bodies show a decrease in rock granulation, in the center-edge direction of the body, usually culminating in aphanitic rocks, which represent, as a rule, the cooling edge of the dyke. Close to these edges, enclaves and tonsils filled with quartz-feldspathic material are frequently observed. The contacts with its host country are abrupt, sometimes marked by the presence of cooling edges, whose thickness varies from a few centimeters to, exceptionally, 2 m. The K-Ar ages of these dykes are: (1) 700 ± 8 Ma in qz-diorite (whole rock); (2) 883 ± 10 Ma in diorite (plagioclase); (3) 1,099 ± 39 Ma in diabase (plagioclase); (4) 1,802 ± 22 Ma in diabase with olivine (mafic concentrate). The first three ages are interpreted as minimum ages for these bodies. The age of 1,802 ± 22 Ma is compatible with the age of 1,707 ± 17 Ma (Rb-Sr in RT) obtained for dacites and porphyry granites. The geochronological data available for the dikes in the Rio Maria region allow placing them in the Proterozoic, and the most reliable ages suggest that at least part of these dikes is contemporary with the anorogenic granitic magmatism. Diabases have been divided into four subtypes: (1) diabase with olivine - exhibits subophytic texture. It consists of labradorite (An55-65), augite + pigeonite, olivine, opaques and hornblende; (2) porphyritic microdiabase - cuts diabase with olivine, formed by plagioclase phenocrysts immersed in a pilotaxitic matrix formed by plagioclase, augite, opaque and amphibole slats; (3)) amphibole-diabase- exhibits a granular texture with a subphytic tendency, is made up of labradorite (An54-64), opaque minerals augite, late amphibole (tremolite-actinolite) and, rarely, hypersthene; (4) auginite-diabase (RJ-18B) with ophitic texture, it is formed by labradorite (An56), augite, opaques and, secondary amphibole. Diorites and quartz-diorites show, in general, a granular texture tending to subphytic or porphyritic with a matrix rich in granophyric intergrowths. Diorites are formed by very saussuritized plagioclase, augite, quartz, hornblende and opaques. Quartz-diorites have similar mineralogy to diorites, differing only in the modal content of quartz and granophyric intergrowths. Some diorites and diabases present plagioclase phenocrysts with sieve texture, suggesting the action of mixing and/or mingling processes. The dacites are formed by porphyry dacites and porphyry dacites rich in mafics. Both have a porphyritic texture, locally glomeroporphyritic, formed by aggregates of plagioclase phenocrysts, quite saussuritized, hornblende locally involving augite, in addition to isolated quartz phenocrysts. The two subtypes have a predominantly granophyritic matrix, sometimes spherulitic. The presence of microcrystalline quartz was noted forming almond-shaped aggregates (spots), attributed to mixing processes. The rhyolites exhibit a porphyritic texture, locally glomeroporphyritic, formed by plagioclase and quartz phenocrysts, immersed in a microcrystalline matrix with a micrographic tendency. Microcrystalline aggregates consisting of chlorite, biotite and opaques also occur. The TAS diagram shows good correlation between the modal classification and the geochemical data. In this diagram the diabases and diorites plot within the field of their volcanic counterparts. Quartz-diorites generally fall into the field of low-silica dacites. The dacites themselves are a little richer in silica than the preceding group, although both focus on the same field. In the AFM diagram the samples are located in the tholeitic subalkaline field. The presence of compositional gaps between groups, mainly between diabases and diorites, and from these to quartz-diorites, reinforces the hypothesis that these rock groups studied do not present a continuous magmatic evolution. The RJ-18B sample, although presenting characteristics of diabase, shows geochemically greater affinities with the diorites. The geochemical data also reinforce the hypothesis that the dikes of Rio Maria, although showing a tholeitic affiliation, were probably generated from different liquids, since the compositional gaps between the various groups are very accentuated. The dacites, although they present, in some diagrams, an overlap with the quartz-diorites, they differ from them petrographically and geochemically, too, and, in terms of occurrence in the field. There is petrographic evidence that the crystallization of diabases was driven mainly by the fractionation of olivine, while in diorites, augite and plagioclase played a dominant role. The petrographic and geochemical data show that the diabases, with the exception of sample RJ-18B, are entirely different from the other groups in terms of magmatic evolution. Diorites and quartz-diorites, in turn, although petrographically similar, present a compositional gap that weakens and immediate hypothesis since the latter represents a more evolved term, derived from the former. Sample RJ-18B is interpreted as a mafic concentrate of these diorites. This hypothesis can be justified by the modal and chemical composition of this sample. Dacites and rhyolites are probably genetically linked to anorogenic granitic magmatism, with probable associated mixing processes, mainly in the case of dacites.
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Granitóides e anfibolitos da Serra do Navio, borda norte do Bloco Arqueano Amapá: caracterização petrográfica e geoquímica, geocronologia Pb-Pb em zircão e isótopos de Nd
(Universidade Federal do Pará, 2009-06-16) TAVARES, Roberta Patrícia dos Santos; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The metavolcanosedimentary sequences from the Serra do Navio, included in the Vila Nova group, and associated granitoids are located in the Central region of the State of Amapá, at the limit between two main geotectonic domains of the Maroni-Itacaiunas Province, Southeastern part of the Guyana Shield (i.e. Archean Amapá Block at south and Paleoproterozoic juvenile domain at north). The Amapá block consists of an extensive Archean continental landmass composed by granulitic and gneissic complexes, orthogneisses and migmatites. The main period of crustal accretion took place at the end of Paleoarchean and along Mesoarchean while reworking processes are dominant during Neoarchean. Two major episodes of magmatism were identified at 2.85-2.79 Ga and 2.66-2.60 Ga, respectively. During the Transamazonian orogenic event ((2.26-1.95 Ga), the Amapá Block underwent granite intrusions, formation of metavolcanosedimentary and high –grade metamorphism episodes. In the Serra do Navio area, the supracrustal sequences of the Vila Nova group occur as NW-SE elongated belts. These sequences are composed by a basal orthoanphibolites and metamafic rocks overlain by quartzschists with lenses of calk-silicated rocks, biotite-schists, graphitic-schists including lenses of calcic and manganesiferous marble. All the units are metamorphosed under greenschist to amphibolite facies. Several bodies of foliated monzogranites and foliated and isotropic granodiorites crosscut the supracrustal sequences. Foliated mongranites and granodiorites exhibit geochemical signature of sub-alkaline, slightly peraluminous granites similar with A type granites (A2 type). Isotropic granodiorites display characteristics of calk-alkaline, peraluminous, fractionated I type granites. Trace and Rare earth elements geochemical data indicated that the amphibolites consists of T- MORB like andesitic basalts and suggest that they formed in extensional context, probably in a retro-arc basin. Sm-Nd isotopic results on five samples of amphibolites furnished _Nd(2.23 Ga) values between +0.91 and +3.55, indicating a major mantle derivation with slight contribution of crustal magmas in the source or crustal contamination during the genesis of these rocks. Schist samples from the same sequences displayed slightly positive to negative _Nd values (-4.98 < _Nd(2.23Ga) < +0.57) pointing to the assimilation of crustal material from the Archean basement or contamination by metamorphic fluids. The Nd isotopic values of _Nd (2.23 Ga) between -4.88 and +3.15, with corresponding TDM Nd model ages from 2.24 Ga up to 2.84 Ga obtained on seven samples from granitoids indicated an important contribution of an Archean crustal component in the source of these rocks, also registered by Archean inherited up to 2.71 Ga, as well as Paleoproterozoic juvenile sources for some of the studied granitoids. Pb-Pb ages on zircon from three samples of monzogranites and granodiorites between 2.23 – 2.25 Ga suggest that they formed during an Eorhyacian episode of magmatism. Such ages also suggest that the Vila Nova supracrustal sequences, in which the granitoids are intrusive, also formed during an early Transamazonian episode and are contemporaneous with the Ipitinga group, at the southern border of the Amapá block and with the “l´ile de Cayenne” mafic rocks in French Guyana. Therefore, the Vila Nova group at the Serra do Navio does not belong to the Mesorhyacian greenstones belt from the Southeastern Guyana shield and constitutes a further evidence of the Eorhyacian stage of oceanic crust formation which began the Transamazonian evolution of the Maroni-Itacaiunas Province.
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Granitos pórfiros da região de vila Riozinho, província aurífera do Tapajós: petrografia e geocronologia
(2008-09) LAMARÃO, Cláudio Nery; SOUZA, Kleber Silva de; DALL'AGNOL, Roberto; GALARZA TORO, Marco Antônio
The Tapajós Gold Province (TGP) is located in the center of the Amazonian craton. It is dominated by Paleoproterozoic calc-alkaline and A-type granitoids and intermediate to felsic volcanic sequences. The Vila Riozinho region, situated in the central-eastern part of the TGP and constituted by the Vila Riozinho, Moraes Almeida and Jardim do Ouro villages, has the more important geologic units that characterize this province. The aim of this paper is to present new petrographic and geochronological data on the porphyry granites associated with the dominant monzogranitic rocks of the Older São Jorge granite and with ignimbrites and rhyolites of the Moraes Almeida Formation and leucogranitic rocks of the Maloquinha suite. The geochronological data revealed at least two distinct periods of generation of porphyry granites in the region. The first, associated with 1.98 Ga calc-alkaline magmatismo, and the second with 1.88 Ga alkaline rocks. Backscattered images and analyses of EDS (energy dispersive spectrometry) obtained with a SEM (scanning electron microscope) showed that is frequent the occurrences of gold particles in the porphyry granites filling cavities in quartz and plagioclase, or associated with epidote and alkali feldspar. These data suggest that the porphyry granites can have contributed to gold mineralization of the Vila Riozinho region, and shows that detailed studies are necessary to elucidate metallogenetic importance of these rocks in the gold mineralization of the region.
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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.
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Petrografia e geoquímica do Granito Pojuca, Serra dos Carajás-PA
(Universidade Federal do Pará, 1998-06-14) HORBE, Marco Antonio; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
The Pojuca Granite outcrops in the northern portion of the Serra dos Carajás, showing intrusive contact with the Archean rocks of the Itacaiúnas Supergroup. The petrographic studies, based on drilling cores, revealed that in the studied portion (sub-outcrop) the body is constituted by monzogranites (MzG), dominant, with variations for monzo and syenogranitic (MzSG) transitional terms, occurring subordinately amphibole-granitoids, alkali -feldspar-granites, pegmatoid rocks and hydrothermalized leucogranites. The rocks are, in general, isotropic, equigranular medium to coarse, pink, very poor in mafics (chlorite±amphibole±tourmaline <7%), constituting leucocratic to hololeucocratic varieties, with very localized brittle deformation. The monzogranites and the monzo to syenogranites are very similar petrographically, however they present different geochemical behavior, marked by the enrichment in K2O and depletion in Na2O in the rocks of facies of the MzSG in relation to the MzG. The amphibole-granitoids show petrographic and chemical characteristics that indicate a hybrid origin, while the alkali-feldspar-granites are related to hydrothermalized portions and occur very locally. The leucogranites (LG) are restricted to the southeast end of the granite and have a well differentiated mineralogical, petrographic and geochemical behavior in relation to the other studied facies. They represent the granite dome, in sharp lower contact with MzG and MzSG, with evidence of being precocious in relation to the other facies, having been fragmented during their placement. LG are medium and fine-grained rocks, pink to cream in color, locally gray or greenish, hololeucocratic (M<2%), being hydrothermalized to varying degrees. Petrographically, two subfacies are distinguished, individualized based on the intensity of the transformations: leucogranites (LG) and intensely hydrothermalized leucogranites (LGIH). Despite the difficulties in distinguishing between primary (magmatic) albite and decalcified plagioclase, which also have an albitic composition, it was concluded, based on petrographic and geochemical evidence, that leucogranites are effectively albite-granites, assuming the hypothesis of their magmatic origin. From the remarkable coincidence of ages between the Pojuca Granite and several anorogenic granites from the Eastern Amazon and the other existing similarities between them, the Pojuca Granite was compared with the Jamon, Musa, Cigano and Serra dos Carajás granites. In terms of modal composition it does not differ from the other granites, however the leucogranites (albite-granites) present in the Pojuca Granite represent a particular variety, which was not registered in the other bodies. The Pojuca Granite exhibits intraplate type A geochemical characteristics and similarities with several anorogenic granites from the Eastern Amazon. Among those chosen for comparison, their greater affinity with the Serra dos Carajás and Cigano granites and the existence of clear differences in relation to the Jamon and Musa granites are clear. Therefore, the existence of geochemical contrasts between the anorogenic granites of the Rio Maria Granite-Greenstone Terrain (TGGRM) and those of the Carajás Block (Pojuca, Serra dos Carajás and Cigano) are confirmed. The albite-granite identified in the Pojuca Granite differs in mineralogical, petrographic and geochemical terms from the other albite-granites described in the Amazon, but this comparison should be deepened in view of the economic and petrological importance that these rocks have.
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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.
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Petrografia, suscetibilidade magnética e química mineral dos metagabros de Águas Claras, Serra dos Carajás-Pará
(Universidade Federal do Pará, 1997-04-15) SOARES, José Erima Bezerra; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
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Petrography of gypsum-bearing facies of the Codó Formation (Late Aptian), Northern Brazil
(2006-09) PAZ, Jackson Douglas Silva da; ROSSETTI, Dilce de Fátima
An original and detailed study focusing the petrography of evaporites from the Late Aptian deposits exposed in the eastern and southern São Luís-Grajaú Basin is presented herein, with the attempt of distinguishing between primary and secondary evaporites, and reconstructing their post-depositional evolution. Seven evaporites phases were recognized: 1. chevron gypsum; 2. nodular to lensoidal gypsum or anhydrite; 3. fibrous to acicular gypsum; 4. mosaic gypsum; 5. brecciated gypsum or gypsarenite; 6. pseudo-nodular anhydrite or gypsum; and 7. rosettes of gypsum. The three first phases of gypsum display petrographic characteristics that conform to a primary nature. The fibrous to acicular and mosaic gypsum were formed by replacement of primary gypsum, but their origin took place during the eodiagenesis, still under influence of the depositional setting. These gypsum morphologies are closely related to the laminated evaporites, serving to demonstrate that their formation was related to replacements that did not affect the primary sedimentary structures. The pseudo-nodular anhydrite or gypsum seems to have originated by mobilization of sulfate-rich fluids during burial, probably related to halokinesis. The rosettes of gypsum, which intercept all the other gypsum varieties, represent the latest phase of evaporite formation in the study area, resulting from either intrastratal waters or surface waters during weathering.