Navegando por Assunto "Metamorfismo (Geologia)"

Agora exibindo 1 - 9 de 9

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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)
Evolução petrológica e estrutural do gnaisse estrela, Curionópolis, PA
(Universidade Federal do Pará, 1991-12-18) BARROS, Carlos Eduardo de Mesquita; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Acesso aberto (Open Access)
Geologia e petrologia do extremo norte da Serra do Estrondo (GO)
(Universidade Federal do Pará, 1984-05-02) SOUZA, Antonio Celso Costa de; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Acesso aberto (Open Access)
Geologia estrutural do Cinturão Araguaia e ao longo da seção compreendida entre as cidades de Marabá e Apinagés
(Universidade Federal do Pará, 1994-08-05) LIMA, Jairo Bezerra de; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286
Acesso aberto (Open Access)
Metamorfismo das rochas pelíticas do segmento setentrional da faixa Paraguai-Araguaia
(Universidade Federal do Pará, 1980-03-20) SILVA, José Maurício Rangel da; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801
Petrographic, petrochemical and microstructural data were used in the study of the metamorphism. In keeping with the work's scalé, the data .are regionally consistent. The metamorphism acted on sedimentary parent rocks, chemically similar to shales and greywacke admixtures. Relict sedimentary structures point to a sedimentary origin. The mineral assembrages distribution in Baixo Araguaia Group shows, from west to east, a regional metamorphic zoning with sericite, chlorite and biotite. Around megastructures (with supposed basement nucleus) a garnet zone has been recognized. The baric type is medium-pressure and corraspodds to Northern Appalachians and Scottish Highlands. Metamorphism and tectonic events are correlativa. The intensity of metamorphism, correspondingly to staurolite and kyanite crystallization, outlasts the deformation F2. The cooling of the meta sedimentary sequence brought out the biotite and muscovite crystallization. The metamorphism is referable to a polyphase cycle. The final manifestations .of the metamorphism belong to the Brasiliano Cycle.
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Petrografia, geoquímica e geocronologia do Granito Ramal do Lontra e sua relação com a tectônica e metamorfismo do Cinturão Araguaia, Xambioá-TO
(Universidade Federal do Pará, 2006-05-24) ALVES, Cleber Ladeira; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
In the portion east of the Cinturão Araguaia in the State of the Tocantins some graníticos bodies of small dimensions are identified, deserving have detached granites Santa Luzia, Ramal do Lontra and Presidente Kennedy, which are the register of an important event of granitogênese related to the evolution of the Cinturão Araguaia in the end of the Neoproterozóic. The Granite Ramal do Lontra, located in the northwest of the State of the Tocantins, approximately the 30 km the Southeast of the city of Xambioá, constitutes a stock of lightly oval form with longer axe of approximately 5 km and smaller axe of 4 km, hosted by quartzitos and micaxistos of the Estrondo Group . The Granite Ramal do Lontra, accord petrographics studies are represented by metagranites with small mineralogical variations, poor in mafics minerals (< 6%), hololeucocratic, equigranular middle, presenting granoblastic texture, predominantly, with texture to reliquiar granular hipidiomorphic. In diagram QAP of Strackeisen, its classification is placed dominant in the field of the monzogranite, or in the limit of the fields monzogranite the granodiorite. The classification most specific detaches muscovite-biotite meta-monzogranites and muscovite-biotite meta-monzogranites the granodiorites. Its mineralogic content is formed essentially by peristeritic plagioclase (An11-16), quartz and microcline, beyond biotite and muscovite. The accessory minerals congregate apatite, zircon, titanite, alanite, monazite, oxide of rare earth element and minerals opacs. The geochemicals data show great composicional homogeneity presenting high values of SiO2, Al2O3, K2O and Na2O, and low values of MgO, Fe2O3Total and TiO2. The diagrams of the geochemistry classification and normative data with the presence of normative coríndon, indicate leucogranitic nature and peraluminous character for the Granite Ramal do Lontra. The study of element-trace showed that it has compositions variations in the rocks of the Granite Ramal do Lontra, what was not evidenced in the elements biggest, where observed a homogeneity in content of such elements. Such study it disclosed to a group of rocks with signature geochemistry distinct of the majority of the rocks of the Granite Ramal do Lontra, possessing high contents of REE, beyond element-trace Nb, Ta and Y, that is reflected petrographicly by the biggest amount of monazite and a rare earth oxide in these rocks. The high content of these elements is possibly related to the contamination of the magma for its hosted rocks during its ascension. The geocronologic study carried through by the method of evaporation of Pb in zircon supplied average age of 549±5 Ma, which is interpreted as the minimum age of crystallization of the zircon and, consequently, of the Granite Ramal do Lontra. This age is similar to gotten in the Granite Santa Luzia enter 550-560 Ma the one that is correlated the same the magmatic event of the Cinturão Araguaia. Combining geologic, petrographics, geochemicals and geocronologics the data of the Granite Ramal do Lontra it is concluded to deal with one granitogênese peraluminous of lodging sin-tectonic to the evolution of the Cinturão Araguaia. This granitogenese also cronologicaly is related to granites of the Suíte Lageado of age 546±6 Ma, situated the Southeast of the Cinturão Araguaia whose bodies are incased in granulítics and gnaissics lands of the paleoproterozoic of the Massif of Goiás, but with geologic, petrographics and geochemicals characteristics different. These varied granitics bodies can be related to a thermal event of great amplitude related to the regional metamorphism in the neoproterozoic of the Cinturão Araguaia, that also affected its basement. Two hypotheses are adopted as possible sources for the Granite Ramal do Lontra. One of them would be for fusing of ortognaisses of the Complex Colméia, and to another one it would involve fusing of the metassediments of the Cinturão Araguaia (Estrondo Group), however not them of pelitic composition, but of composition the quartz-feldspatic.
Acesso aberto (Open Access)
Petrologia e geotermobarometria das rochas metamórficas do Cinturão Araguaia: região de Xambioá-Araguanã (TO)
(Universidade Federal do Pará, 2016-12-16) PINHEIRO, Bruno Luís Silva; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
In order to contribute to the understanding of the metamorphic processes of the metamorphic rocks of the Araguaia Belt (CA), this thesis presents field data and metamorphic modeling, used as tools to obtain the maximum conditions of P-T reached by the units located in the Xambioá-Araguanã (TO) region of the rocks studied are five samples of Staurolite-garnetbiotite- muscovite-schist with Kyanite and a sample of Garnet amphibolite, belonging to the Xambioá Formation and Xambica Suite, respectively. The study of the metamorphism occurred through petrographic, chemical analyzes of rocks and minerals of the main associations of pelitic rocks, semipelitic and mafic rocks that comprise the zone of greater metamorphic degree of CA, for later analysis by metamorphic modeling in the NCKFMASH system and optimized geothermobarometry, In the avPT mode, in the THERMOCALC program, as well as the Hb-Pl software, which made it possible to identify PT metamorphic peak conditions. In addition to defining an approximate age of metamorphism using the Ar-Ar method in biotite and amphibole. The petrographic-mineralogical study identified the main mineral parageneses in the studied micaxists, such as St + Grt + Bt + Ms + Qtz ± Pl (An12-31) + Ky, and in the amphibolites Hb + Grt + Bt + Pl (An12-25). The mineral chemistry results showed that the pomegranate composition of the six samples is dominated by the almandide molecule, which is followed by pyropo, thickenstock, and andradite, increasing Fe2 + and Mg from the nuclei to the edges, with a concomitant decrease of Mn and Ca. The higher Fe and Mg contents towards the edges indicate an increase in the temperature conditions during mineral development. The composition of the biotite is in the transition of the biotite with phlogopite, becoming more ferromagnesian mica. Staurolite from the core to the border is enriched in Fe2 + and depleted in Mg, which may suggest reactions in contact with the matrix and / or with micas or grenades. Metamorphic modeling in the NCKFMASH system resulted in pseudosections with similar topologies for samples BP002, BP149 and BP299, suggesting that the maximum metamorphic conditions they were subjected to are similar, being situated within a PT window with pressure approximately between 7 and 9 kbar and temperature between 630 and 665 ° C. The models of composite isopleths of the minerals calculated in the pseudosections indicate a higher participation of Mg and a lower participation of Ca in the composition of the main minerals according to the increase of the metamorphic P-T conditions in the region, compatible with the mineral chemistry results of the studied rocks. In addition to the plagioclase and the pomegranate of the sample BP002 presenting as good indicators of metamorphism conditions, with values of 8 kbar and 660 °C, in which the coreedge variation of Ca and Na in plagioclase crystals and the variation Core-edge in the iron content of the grenades show a progressive barometric-type metamorphic trajectory, represented by a small slope curve, coming from the trivariant field Chl + Grt + Bt + Ms. PT estimates obtained in the avPT mode of THERMOCALC in all the selected samples (BP002, BP005, BP149, BP149, BP299, BP006), as well as in the Hb-Plag software in the amphibolites (BP006), presented enough Consistent and consistent with calculations of metamorphic peak conditions via THERMOCALC for rocks in the Xambioá-Araguanã region, although there are discrepancies in the calculated results. All calculated P-T results are compatible with the field of the amphibolite facies of the mean P-T series, typical of continental orogenic belt environments and therefore characteristic of continental collisions. Metamorphic conditions are reinforced with the mineral chemistry results of calcium amphiboles suggesting the same average pressure conditions of the Dalradian terrain of Scotland. The air-air ages in minerals obtained in the metapelites and amphibolites in this thesis were similar, around 504 Ma, and they show that the peak of the metamorphism of the amphibolite facies in the region under study has an older age and they suggest that it was next to the Neoproterozoic-Paleozoic interface, because these Ar-Ar ages obtained are younger ages than the K-Ar ages of 520-560 Ma, interpreted as relating the metamorphism of the CA with the Brasilian thermo-tectonic event, and because it is within the error of the U-Th-Pb monazites chemical age in feldspathic schist biotite from an area near the city of Presidente Kennedy (TO), 513 ± 14 Ma interpreted only at a younger age than the mean age evaluated for the metamorphism of the Araguaia Belt (550 - 530 Ma).
Acesso aberto (Open Access)
Polyphase deformation and metamorphism of the Cuiabá group in the Poconé region (MT), Paraguay Fold and Thrust Belt: kinematic and tectonic implications
(Universidade Federal do Pará, 2015-03) VASCONCELOS, Bruno Rodrigo; RUIZ, Amarildo Salina; MATOS, João Batista
Several deformation models have been proposed for the Paraguay Belt, which primarily differ in the number of phases of deformation, direction of vergence and tectonic style. Structural features presented in this work indicate that the tectonics was dominated by low dip thrust sheets in an initial phase, followed by two progressive deformation phases. The first phase of deformation is characterized by a slate cleavage and axial plane of isoclinal recumbent folds with a NE axial direction, with a recrystallization of the minerals in the greenschist facies associated with horizontal shear zones with a top-to-the-SE sense of movement. The second stage shows vergence towards the NW, characterized by crenulation cleavage axial plane to F2 open folds over S0 and S1, locally associated with reverse faults. The third phase of deformation is characterized by subvertical faults and fractures with a NW direction showing sinistral movement, which are commonly filled by quartz veins. The collection of tectonic structures and metamorphic paragenesis described indicate that the most intense deformation at the deeper crustal level, greenschistfacies, occurred during F1, which accommodated significant crustal shortening through isoclinal recumbent folds and shear zones with low dip angles and hangwall movement to the SE, in a thin-skinned tectonic regime. The F2 deformation phase was less intense and had a brittle to ductile behavior that accommodated a slight shortening through normal open subvertical folds, and reverse faults developed in shallower crustal level, with vergence towards the Amazonian Craton. The third phase was less pervasive, and the shortening was accommodated by relief subvertical sinistral faults.
Acesso aberto (Open Access)
Proveniência e idade do metamorfismo das rochas da Faixa Brasília, na Região de Tapira (SW de Minas Gerais)
(2006-07) SILVA, Carlos Humberto da; SIMÕES, Luiz Sergio Amarante; KRYMSKY, Robert Shamilevich; MACAMBIRA, Moacir José Buenano
The Brasília Fold Thrust Belt at Tapira area (SW of Minas Gerais State, Brazil) has four different litho-tectonic domains imbricated by thrust faults with vergency to the São Francisco Craton. Sm/Nd isotopic studies were undertaken and the results show different model and metamorphic ages for the thrust sheets. Rocks from the lower thrust sheet yield a metamorphic age of 543 Ma while the upper thrust sheet has a metamorphic age of 581 Ma. The TDM model ages are similar for both thrust sheets, between 1.7 and 2.2 Ga. Because of their lithologic characteristics, the thrust sheets are interpreted as having been deposited in a distal continental platform environment, their main source being Paleoproterozoic rocks of the São Francisco Craton. The upper thrust sheet rocks presents a metamorphism age of 612 Ma and a bimodal distribution of TDM model ages between 1.3 and 1.9 - 2.0 Ga, respectively. The lithologic and isotopic characteristics of this thrust sheet the rocks are interpreted as a result of deposition on a continental slope or oceanic floor environment, with mixed contributions from Paleo - and Mesoproterozoic rocks of the São Francisco Craton. In spite of the small number of analyzed samples and the uncertainties inherent to the Sm/Nd method the metamorphisms are not considered to be synchronous in the different thrust sheets. This is to be expected in a thrust belt system, in which the more metamorphosed thrust sheets are juxtaposed to less metamorphosed ones.