Navegando por Autor "LAFON, Jean Michel"

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Cerro Porã Batholith: post-orogenic A-type granite from the Amoguijá Magmatic Arc - Rio ApaTerrane - South of the Amazonian Craton
(2013-09) PLENS, Dalila Pexe; RUIZ, Amarildo Salina; SOUSA, Maria Zélia Aguiar de; BATATA, Maria Elisa Fróes; LAFON, Jean Michel; BRITTES, Ana Flávia Nunes
The Cerro Porã Batholith has an approximately area of 30 km by 4 km, situated at the region of Porto Murtinho, Mato Grosso do Sul. It is located in Rio Apa Terrane, at the southern portion of the Amazonian Craton. It consists of Pink Syenogranitic Facies and Gray Monzogranitic Facies. The first facies is characterized by xenomorphic equigranular texture to essentially inequigranular texture with graphic and granophiric intergrowths. Both facies are composed of alkali feldspar, quartz, and plagioclase with biotite as the only primary mafic mineral. The Gray Monzogranitic Facies has porphyritic texture with graphic to granophiric fine-grained groundmass. It consists of quartz, plagioclase, alkali feldspar, and mafic aggregates (biotite and amphibole). Both facies were metamorphosed at greenschist facies and the Pink Syenogranitic Facies, which is milonytic in nature when it is in shear zones. One event of ductile–brittle deformation was identified, originated in a compressive system. It was responsible for the schistosity and mineral-stretching lineation. The development of the Esperança shear zone is related to this deformational phase and reflects the cinematic history of the reverse convergent system with top transport to NWW. Chemically, these rock types are classified as A2-type granitoids of range alkaline potassium saturated on silica. Geochronological data obtained by U-Pb (Sensitive High Resolution Ion Microprobe) method in zircon resulted in an age of 1749 ± 45 Ma, interpreted as crystallization age of the batholith. From the geotectonic point, the Cerro Porã Granite is considered to be the product of a magmatism associated with a magmatic arc developed in Statherian and emplaced in late-orogenic to post-orogenic stage.
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Datação Sm-Nd em rocha total e granada do metamorfismo granulítico da região de Tartarugal Grande, Amapá Central
(2008-03) OLIVEIRA, Elma Costa; LAFON, Jean Michel; GIOIA, Simone Maria Costa Lima; PIMENTEL, Márcio Martins
The experimental procedure for Sm-Nd method performed at the Pará-Iso Isotope Geology laboratory, (Federal University of Pará) is described in details as a reference for the customers of the Pará-Iso. Sm-Nd dating of felsic granulites from the Tartarugal Grande area, northeastern of the Archean Amapá Block, (Southeastern Guyana Shield) furnished whole rock - garnet isochron ages of 2017 ± 12 Ma, 1981.6 ± 2.8 Ma e 2018 ± 2.3 Ma. Dating of the same samples at the UnB geochronological laboratory yielded ages of 2037 ± 8.4 Ma, 1988 ± 11 Ma e 2013 ± 15 Ma, respectively. Such results indicate that temperature of at least 700°C was reached by the Tartarugal Grande granulites between 2.04 - 1.98 Ga, as a proxy of a late Transamazonian high grade metamorphic event in the northeastern sector of the Archean Amapá Block. TDM(Nd) model ages between 3.15 Ga and 2.79 Ga are a further evidence of a major Mesoarchean crustal growth episode in the southeastern Guyana Shield.
Acesso aberto (Open Access)
Distribuição e assinatura isotópica de Pb em sedimentos de fundo da Foz do Rio Guamá e da Baía do Guajará (Belém - Pará)
(2012) SANTOS, Suziane Nascimento; LAFON, Jean Michel; CORRÊA, José Augusto Martins; BABINSKI, Marly; DIAS, Fabiana Ferrari; TADDEI, Maria Helena Tirolo
Lead analyses in bottom sediments from the hydrographic system of Belem (Para) indicated low contents of this metal for the sediments from the Guama river, with no significant anthropogenic contribution. A concentration of 18.1 ± 1.5 mg kg-1 and 206Pb/207Pb isotopic signature of 1.196 ± 0.002 are assigned for Pb from natural sources. On the other hand, the significant increase of Pb contents in the sediments from the Guajará bay, together with the decrease of 206Pb/207 ratios (1.172 < 206Pb/207 < 1.188) point to an anthropogenic lead contribution, originated by the industrial and urban activities of the city of Belem.
Acesso aberto (Open Access)
Distribution and isotopic composition of lead in bottom sediments from the hydrographic system of Belém, Pará (western margin of Guajará Bay and Carnapijó River)
(Universidade Federal do Pará, 2016-06) OLIVEIRA, Elma Costa; LAFON, Jean Michel; CORRÊA, José Augusto Martins; CARVALHO, Jully Hellen dos Santos
This study first aimed to evaluate the effect of human activities on the distribution of lead within the estuarine system of Belém, Pará. This was achieved by studying the concentration and isotopic signature of Pb in bottom sediments from the western margin of Guajará Bay and from Carnapijó River, an area removed from the influence of the city of Belém. Secondly, the contribution of suspended matter in the transportation of anthropogenic Pb in Guajará Bay was evaluated. Third, the content and background isotopic signature of Pb in the hydrographic system of Belém was determined. Isotopic signatures of sediments from the western margin of Guajará Bay confirm an anthropogenic contribution of Pb throughout the entire bay. The Pb accumulation process has become more efficient over the last 10 years, and this can be attributed to the rapid population growth of Belém city. Sediments in Carnapijó River are not affected by human activities, and the average concentration values (Pb = 19.6 ± 3.7 mg kg-1) and isotopic signatures (206Pb/207Pb = 1.196 ± 0.004) confirm the background Pb values previously proposed for the river system in the Belém region. The isotopic signatures of suspended matter on the eastern (206Pb/207Pb = 1.188) and western (206Pb/207Pb = 1.174) margins of Guajará Bay show that suspended matter is an efficient Pb transportation mechanism of domestic and industrial wastewater from Belém to the western margin of the Bay due to tidal effects at the confluence with Guamá River.
Acesso aberto (Open Access)
Geology, petrology and geochronology (Pb-Pb) of the Serra da Bocaina Formation: evidence of an Orosirian Amoguijá Magmatic Arc in the Rio Apa Terrane, south of the Amazonian Craton
(2013-03) BRITTES, Ana Flávia Nunes; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; BATATA, Maria Elisa Fróes; LAFON, Jean Michel; PLENS, Dalila Pexe
This work presents the results of the geological mapping and the petrological characterization of the Serra da Bocaina Formation belonging to the Amoguijá Magmatic Arc of the Rio Apa Terrain. In the Bocaina hills, the Serra da Bocaina Formation consists of intermediately to predominately acidic volcanic rocks, classified as andesites and rhyolites and subdivided into five petrographic facies, which include four volcanoclastics and one effusive. In the studied rocks, tectonic structures are generated in two compressive ductile to ductile-brittle deformational phases. The first phase, which is more intense, presents along the entire studied area and is responsible for the Santa Rosa Shear Belt, whereas the second phase is more localized. The geochemical study indicates a calc-alkaline magmatism of medium to high K, peraluminous, and generated in a volcanic arc environment. These volcanic rocks formed in an explosive environment related to the Amoguijá Magmatic Arc, as indicated by their Pb-Pb zircon age of 1877.3 ± 3.9 Ma.
Acesso aberto (Open Access)
Geology, petrology, U-Pb (shrimp) geochronology of the Morrinhos granite -Paraguá terrane, SW Amazonian craton: implications for the magmatic evolution of the San Ignácio orogeny
(2014-09) FRANÇA, Ohana; RUIZ, Amarildo Salina; SOUSA, Maria Zélia Aguiar de; BATATA, Maria Elisa Fróes; LAFON, Jean Michel
Morrinhos granite is a batholith body that is slightly elongated in the NNW direction and approximately 1,140 km2 long; it is located in the municipality of Vila Bela da Santíssima Trindade of the state of Mato Grosso, Brazil, in the Paraguá Terrane, Rondonian-San Ignácio Province, in the SW portion of the Amazonian Craton. This intrusion displays a compositional variation from tonalite to monzogranite, has a medium to coarse inequigranular texture and is locally porphyritic; biotite is the predominant mafic in one of the facies, and hornblende is predominant in the other, with both metamorphosed into the greenschist facies. The studied rocks characterize an intermediate to acidic sequence that was formed by a subalkaline magmatism; the series is alkali-calcic to metaluminous to slightly peraluminous, and the rocks evolved through fractioned crystallization mechanisms. The structural data show two deformation phases represented by penetrative foliation (S1) and open folds (D2), and both phases were most likely related to the San Ignácio Orogeny. The geochronological (U-Pb SHRIMP) and isotopic (Sm-Nd) investigations of these rocks indicated a crystallization age of 1350 ± 12 Ma, TDM of approximately 1.77 Ga and εNd(1.35) with a negative value of -2.57, suggesting that their generation was related to a partial melting process of a Paleoproterozoic (Statherian) continental crust. The results herein indicate that the Morrinhos granite was generated in a continental magmatic arc in a late- to post-orogenic stage of the San Ignácio Orogeny, and it can be recognized as belonging to the Pensamiento Intrusive Suite.
Acesso aberto (Open Access)
Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS
(Universidade Federal do Pará, 2015-09) REDES, Letícia Alexandre; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; LAFON, Jean Michel
The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS), near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1) and the other brittle (F2). Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga) values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
Uranium-lead dating method at the Pará-Iso isotope geology laboratory, UFPA, Belém – Brazil
(2007-03) KRYMSKY, Robert Shamilevich; MACAMBIRA, Moacir José Buenano; LAFON, Jean Michel; ESTUMANO, Gérson dos Santos
Analytical procedures for U-Pb isotope dilution analyses at the Pará-Iso isotope geology laboratory of the Federal University of Pará (UFPA) are described in detail. The procedures are applied to zircon, titanite, rutile, apatite, columbite-tantalite and whole rock. Reagent preparation and chemical processing are done in clean-room conditions. Samples are dissolved using Teflon™ microcapsules in steel jacket Teflon™ Parr Instrument™ bomb or Teflon™ screw cap containers. U and Pb are separated using anion exchange AG 1x8 resin columns. Typical blanks for mineral sample amounts of 0.01 to 1.0 mg are less than 1 pg U and 20-30 pg Pb. Isotope analysis of the U and Pb from the same filament are carried out using a Finnigan MAT 262 mass-spectrometer in static and dynamic modes. The current analytical level is demonstrated on analyses of international standard zircon 91500 with three different 235U-205Pb and 235U-208Pb isotope tracers and whole rock standards. Results of analyses of two zircon samples are also presented.
Acesso aberto (Open Access)
Vulcanismo félsico paleoproterozoico do Grupo Iricoumé, Domínio Erepecuru-Trombetas, Província Amazônia Central: dados de campo, caracterização petrográfica e geocronologia Pb-Pb em zircão
(2013-03) BARRETO, Carla Joana Santos; LAFON, Jean Michel; COSTA, Lúcia Travassos da Rosa; LIMA, Evandro Fernandes de
The Iricoumé group consists of very well preserved pyroclastic and effusive volcanic rocks as a part of an extensive volcano-plutonic event, which marked the central part of the Amazonian craton during the Orosirian. Such rocks occur in the southern part of the southwestern of Erepecuru-Trombetas Domain (NW of the Pará state), south of the Guyana Shield. Petrographic study allows distinction of two volcanic types. A dominant explosive volcanism is characterized by pyroclastic rocks (ignimbrites, rheoignimbrites, lapilli-tuff related to surge deposit, and co-ignimbrite fall tuff) while a subordinated effusive volcanism is represented by coherent lavas flows and hypabissal rocks (andesites, lamprophyres and latites). Most of the pyroclastic rocks exhibit features of deposition under high temperature suggesting formation in a caldera-related environment. Pb-Pb zircon ages of 1888 ± 2.5 and 1889 ± 2 Ma have been obtained for the formation of trachydacitic ignimbrites and confirm that the dominant volcanism is part of the Iricoumé group. The Pb-Pb zircon age of 1992 ± 3 Ma yielded by an andesite points to the occurrence in the area of an older Orosirian magmatic episode, which has been previously recognized locally southward in the Tapajós domain. These new results constitute a further evidence of the wide extent of the Iricoumé group and correlated volcanic rocks in the central part of the Amazonian craton, and reinforce the assumption that this volcanic episode and correlated magmatism may be considered as a silicic large igneous province (SLIP), as previously proposed by some authors.