DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Item Mesoarchean migmatites of the Carajás Province : from intra-arc melting to collision.(2021) Silva, Marco Antonio Delinardo da; Monteiro, Lena Virginia Soares; Santos, Ticiano José Saraiva dos; Moreto, Carolina Penteado Natividade; Sousa, Soraya Damasceno; Faustinoni, Jackeline Monteiro; Melo, Gustavo Henrique Coelho de; Xavier, Roberto Perez; Toledo, Benfica A. M.In the Carajás Domain, northern Carajás Province, Amazonian Craton, the oldest units encompass the Mesoarchean migmatites of the Xicrim-Cateté Orthogranulite and Xingu Complex. The Xicrim-Cateté Orthogranulite underwent early dehydration and late water-fluxed partial melting. The first process resulted in net-structured and schollen migmatites with a pargasite-bearing mafic granulite paleosome. The F-pargasite breakdown produced a neosome with peritectic enstatite, diopside, and plagioclase and a residual amphibole-free mafic granulite. The late water- fluxed partial melting generated quartzofeldspathic leucosomes in shear bands of the NW-SE-trending high-angle transcurrent shear zones. The Xingu Complex is composed of stromatic, net-structured, schollen and schlieren migmatites developed in the late water-fluxed partial melting event. These migmatites have orthogneiss and am- phibolite paleosome and syn-tectonic quartzofeldspathic leucosome and biotite-rich melanosome oriented along a low angle NE-SW to NW-SE gneissic foliation. The Xicrim-Cateté paleosome age remains undefined, but the U–Pb zircon ages of the pyroxene-bearing neosome constraint the dehydration-melting to c. 3.06–2.93 Ga. The εHf data (−2.2 to +1.2) of the neosome tie the dehydration-melting of the pargasite-bearing granulite to the underplate of mantle melts. The Zr-Ti-Y content and Ti/V ratios of the pargasite-bearing granulite suggest a compositional shift of their protoliths from MORB to IAT, characterizing a scenario of subduction installation and magmatic evolution. The Xicrim-Cateté pyroxene-bearing neosome is geochemically similar to the Xingu orthogneiss. Both rocks have a TTG affinity and similar εHf values (+0.8 to +1.6) and crystallization ages (2.94 Ga). It indicates a common source for them and suggests that the dehydration partial melting of the primitive mafic crust produced a signif- icant portion of the TTG felsic continental crust of the Carajás Domain. It probably occurred during the island-arc setting evolution between 3.06 and 2.93 Ga when supra-subduction mantle melts started to trigger the composi- tional differentiation of the mafic crust. The late water-fluxed partial melting was controlled by fluid influx into the structures developed during the regional deformation of the Carajás Domain at c. 2.89–2.85 Ga, likely associated with a collisional event in the Carajás Province.Item Petrography, geochemistry and geochronology of the potassic granitoids of the Rio Itacambiruçu Supersuite : implications for the Meso- to Neoarchean evolution of the Itacambira-Monte Azul block.(2018) Bersan, Samuel Moreira; Danderfer Filho, André; Abreu, Francisco Robério de; Lana, Cristiano de CarvalhoIn the Itacambira-Monte Azul block (BIMA) the Archean rocks are represented by tonalite-trondhjemite-granodiorite (TTGs) of the Porteirinha Complex and by potassic granitoids of the Rio Itacambiruçu Suite that crop out at the Pedra do Urubu (PUp), Rio Gorutuba (RGp), Barrocão (BAp) and Lagoa Nova (LNp) plutons. This work presents new data for the PUp, RGp and BAp. The petrographic and lithochemical analyses allowed the subdivision of the Rio Itacambiruçu Suite in two groups of granitoids: a medium potassium group, represented by the PUp and RGp, and a high potassium group, in which the BAp rocks are inserted. The geochronological data showed different ages for the medium and high potassium groups, with crystallization ages at ca. 2.92 Ga and 2.65 Ga, respectively. Despite the differences observed between these two groups, the chemical signatures of these rocks are compatible with the signature of biotite-granites generated by the reworking of ancient continental crust. Thereby, the data obtained in this work, added to some previously published results, allowed to the identification of two Archean crustal stabilization events recorded in BIMA, one of Mesoarchean age and the other of Neoarchean age. In addition, we propose the lithodemic reclassification of the Rio Itacambiruçu Suite to Rio Itacambiruçu Supersuite.Item Provenance and age delimitation of Quadrilátero Ferrífero sandstones based on zircon U–Pb isotopes.(2006) Hartmann, Leo Afraneo; Endo, Issamu; Suita, Marcos Tadeu de Freitas; Santos, João Orestes Schneider; Frantz, José Carlos; Carneiro, Maurício Antônio; McNaughton, Neal Jesse; Barley, Mark E.The Quadrilátero Ferrífero has some of the largest iron and gold deposits in the world and is a major geotectonic unit of the São Francisco Craton in Brazil. U–Pb zircon SHRIMP geochronology of six detrital sedimentary and metasedimentary rocks (114 zircon crystals, 118 spot analyses) has improved the understanding of the sedimentary processes and provenance ages of both rocks and the associated iron formation. The age of deposition of the iron formation is constrained between 2.58 and 2.42 Ga. The presence of an old Paleoarchean crust is dated in detrital zircon crystals, including the oldest zircon in South America (3809G3 Ma). Only high-Th/U, magmatic zircon crystals are present in the dated sedimentary rocks, and these indicate that the crust of the region was formed mostly during the Jequie´ cycle (six age peaks between 3055 and 2635 Ma). This time span ofw420 m.y. is similar to the duration of a long-lived Wilson cycle. Most of the Rio das Velhas Basin was filled during approximately 30 m.y. between 2746 and 2717 Ma, though volcanism probably started earlier. The youngest detrital zircon age from the Minas Supergroup indicates that the intracratonic basin fill, including the iron formation, was deposited after 2580 Ma. Therefore, the crust was cratonized shortly after the intrusion of minor granitic bodies at around 2.62–2.58 Ga. A large gap in orogenic activity is indicated by the absence of zircon ages of 2580–2182 Ma.Item New evidence of Neoarchean crustal growth in southern São Francisco Craton : the Carmópolis de Minas Layered Suite, Minas Gerais, Brazil.(2013) Goulart, Luís Emanoel Alexandre; Carneiro, Maurício Antônio; Endo, Issamu; Suita, Marcos Tadeu de FreitasA Suíte Acamadada Carmópolis de Minas está situada no domínio do Complexo Metamórfico Campo Belo, Minas Gerais, SE-Brasil, que, junto a outros complexos metamórficos nos arredores do Quadrilátero Ferrífero, compõem a crosta siálica arqueana da parte meridional do Craton São Francisco. Essa suíte compreende um segmento remanescente de arco magmático, deformado e metamorfisado em fácies anfibolito-superior a granulito. Exibe estratos acamadados e maciços, constituídos por litotipos com assinatura litogeoquímica equivalente a uma série tholeiítica de baixo-K2O. Uma fase de magmatismo tholeiítico e outra de magmatismo cálcio-alcalino foram identificadas. Uma amostra de anfibolito e duas de metarriolito foram utilizadas para datação U-Pb em zircões usando MC-LA-ICP-MS. O anfibolito apresentou zircões com razões 232Th/238U ≈ 0,17 – 0,83 e idade concórdia de 2.752 ± 18 Ma. Esse resultado foi interpretado como idade mínima da fase tholeiítica. As amostras de metarriolito apresentaram zircões com razões 232Th/238U ≈ 0,25 – 0,66 e foram datadas em 2.713 ± 9,9 e 2.710 ± 31 Ma. Esse intervalo fornece uma aproximação para a idade mínima da fase cálcio-alcalina. Uma das amostras de metarriolito apresentou duas populações de zircões herdados. Essas populações foram datadas em 3.374 ± 30 e 2.859 ± 23 Ma, sugerindo a contribuição de crostas mais antigas na gênese da suíte. Os resultados demonstram que a gênese dessa suíte representa um episódio de formação de crosta juvenil durante o Evento Tectonotermal Rio das Velhas (2.780 Ma). Esse episódio sin a tardi-orogênico envolveu desenvolvimento de arco, magmatismo tholeiítico a cálcio-alcalino, metamorfismo e reciclagem crustal.