DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Petrogênese e idade química U-Th-Pb dos pegmatitos de Itambé (BA) registradas pela monazita.(2020) Ferreira, Rafael de Magalhães Gomes; Chaves, Alexandre de Oliveira; Cipriano, Ricardo Augusto Scholz; Gonçalves, Guilherme de OliveiraImagens de elétrons retro-espalhados e microanálises químicas por microssonda eletrônica foram obtidas a partir de cristais de monazita pertencentes aos pegmatitos Bananeira, Itambé, Coqueiro, Cavada e Paraíso do município de Itambé-BA, inseridos na Província Pegmatítica Oriental Brasileira (PPOB). Os cristais mostram-se homogêneos, ou seja, livres de domínios/zoneamentos composicionais e seus teores de U, Th e Pb permitiram a obtenção de idade química média de 502 Ma para o distrito pegmatítico de Itambé. Seus padrões de terras raras normalizados ao condrito mostram anomalia positiva de Sm, elemento fortemente particionado em anfibólio. Esta anomalia sugere que no contexto pós-colisional do Orógeno Araçuaí houve a fusão parcial da rocha encaixante biotita-hornblenda gnaisse durante o processo de descompressão regional associado ao colapso do orógeno, gerando um magma granítico hidratado o bastante para permitir o avolumado crescimento de cristais dos pegmatitos de Itambé, incluindo a monazita. Este mineral atua, portanto, não só como um geocronômetro, mas também como importante indicador petrogenético dos pegmatitos estudados.Item Petrology of the Afonso Cláudio intrusive complex : new insights for the Cambro-Ordovician post-collisional magmatism in the Araçuaí-West Congo Orogen, Southeast Brazil.(2020) Aranda, Ramon de Oliveira; Chaves, Alexandre de Oliveira; Medeiros Junior, Edgar Batista de; Venturini Junior, R.The Afonso Cláudio Intrusive Complex (ACIC) is an igneous body located in the Espírito Santo state, Southeastern Brazil. It is inserted in the geological setting of the post-collisional G5 plutonic Supersuite, related to the extensional collapse stage of the Araçuaí-West Congo Orogen (AWCO). This study presents integrated data of field relationships, petrography, whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes that contributed to understand ACIC petrology. The ACIC intruded in pre-collisional orthogneisses and Nova Venécia Complex paragneisses of the AWCO. It is constituted by two monzogabbro/monzodiorite off-centered mafic cores surrounded by quartz monzonite. Mingling and mixing zones were mapped between these rocks, where jotunite and quartz mangerite occur. Host rock enclaves are observed enclosed by monzogabbro, monzodiorite and quartz monzonite, as well as monzogabbro/monzodiorite enclaves in the quartz monzonite. The ACIC rocks are enriched in LILE and LREE, showing alkali-calcic post-collisional geochemical signature. Zircon U-Pb dating revealed crystallization ages of 480.9 ± 3.2 Ma related to quartz monzonite and 496.5 ± 3.6 Ma to monzogabbro. Both rocks show negative zircon εHf (t) values (with average values of −11.78 and −10.41, respectively) and TDM ages of 1.79 Ga to quartz monzonite and 1.72 Ga to monzogabbro. Supported by presented data, two models can be proposed to the ACIC evolution during the collapse stage of the AWCO and both considering crustal contamination, mixing/mingling and assimilation associated to fractional crystallization. One is based on coeval mantle and crustal melting, with magmas interaction to generate an alkali-calcic magma, whose crystallization produced the monzogabbro and monzodiorite. With the continuity of the orogeny collapse, these mafic rocks would have melted and contributed to generate felsic magmas that crystalized as quartz monzonite. The second one argues in favor to mantle magma intrusion in a magmatic chamber where the nearby crustal rocks melted and the different magmas interacted between them. Monzogabbro and monzodiorite would have been generated by fractional crystallization of the mafic magmas and the quartz monzonite by crystallization of the felsic magmas. Due to the similarities among the post-collisional plutons in the AWCO, the proposed models may explain the petrogenesis of other similar plutons in this orogenic system.Item Metamorphic record of collision and collapse in the Ediacaran‐Cambrian Araçuaí orogen, SE‐Brazil : insights from P–T pseudosections and monazite dating.(2017) Peixoto, Eliza Inez Nunes; Alkmim, Fernando Flecha de; Soares, Antônio Carlos Pedrosa; Lana, Cristiano de Carvalho; Chaves, Alexandre de Oliveirahe Araçuaí orogen is the Brazilian counterpart of the Araçuaí‐West Congo orogenic system (AWCO), a component of the Ediacaran‐Cambrian orogenic network formed during the amalgamation of West Gondwana. The northwestern portion of the Araçuaí orogen is dominated by a succession of metasedimentary rocks made up of Meso‐ to Neoproterozoic rift, passive margin and syn‐orogenic sequences, locally intruded by post‐collisional granites. These sequences are involved in three distinct tectonic units, which from west to east are: the southern Espinhaço fold‐thrust system (SE‐thrust system), the normal‐sense Chapada Acauã shear zone (CASZ) and the Salinas synclinorium. Three deformation phases were documented in the region. The first two phases (D1 and D2) are characterized by contractional structures and represent the collisional development stage of the orogen. The third phase (D3) is extensional and currently viewed as a manifestation of orogenic collapse of the system. The distribution of the metamorphic mineral assemblages in the region characterizes two metamorphic domains. The M‐Domain I on the west, encompassing the SE‐thrust system and the CASZ, is marked by a syn‐collisional (syn‐D1) Barrovian‐type metamorphism with P–T conditions increasing eastwards and reaching ~8.5 kbar at ~650°C between 575 and 565 Ma. The M‐Domain II comprises the Salinas synclinorium in the hangingwall of the CASZ, and besides the greenschist facies syn‐collisional metamorphism, records mainly a Buchan‐type metamorphic event, which took place under 3–5.5 kbar and up to 640°C at c. 530 Ma. The northwestern Araçuaí orogen exhibits, thus, a paired metamorphic pattern, in which the Barrovian and Buchan‐type metamorphic domains are juxtaposed by a normal‐sense shear zone. Lithospheric thinning during the extensional collapse of the orogen promoted ascent of the geotherms and melt generation. A large volume of granites was emplaced in the high grade and anatectic core of the orogen during this stage, and heat advected from these intrusions caused the development of Buchan facies series over a relatively large area. Renewed granite plutonism, hydrothermal activities followed by progressive cooling affected the system between 530 and 490 Ma.Item An assessment of monazite from the Itambé pegmatite district for use as U–Pb isotope reference material for microanalysis and implications for the origin of the “Moacyr” monazite.(2016) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Marinho, Moacyr Moura; Chaves, Alexandre de Oliveira; Valeriano, Claudio de Morisson; Nalini Júnior, Hermínio AriasLarge quantities of monazite from different pegmatite bodies of the Itambe pegmatite district were investigated to assess their suitability as U–Pb and Sm–Nd isotope reference materials for LA-ICP-MS and to track the origin of a piece of theMoacyrmonazite (termed here Itambé), awidely used reference material for LA-ICP-MS U–Pb geochronology. Monazite fromthe largest pegmatite bodies in the district (the Bananeira, Coqueiro and Paraíso pegmatites) are Ce-monazite, with negligible amounts of the huttonite and brabantite components. They are homogeneous in major and trace elements, which makes them potential candidates as compositional reference materials. U–Pb LA-ICP-MS and ID-TIMS analyses yielded identical ages within error. Although the ID-TIMS ages (507.7 ± 1.3 (207Pb⁎/235U) and 513.6 ± 1.2 Ma (206Pb⁎/238U)) were reversely discordant, spot ages determined by LA-ICP-MS geochronology were concordant at ca 508 Ma. The Bananeiro monazite was assessed as a LA-ICPMS U–Pb primary reference material against other known reference materials (treated as unknowns). This approach successfully reproduced the previously published ages of the reference materials.MREE/HREE fractionation (ie, (La/Gd)N and (Gd/Lu)N values), Eu/Eu⁎ and the chondrite-normalized REE patterns suggest that the “Itambé” monazite aliquot is very similar to that fromthe Coqueiro pegmatite. This similarity is likewise apparent in their Sm–Nd isotope compositions. Moreover, the εNdi values of the “Itambé” monazite fragment (εNdi=−4.2) and those fromall the major pegmatites in the district, are distinct fromother reference materials (eg, Managountry; εNdi = −22.3) as well as gem-quality monazite from c. 490–520 Ma pegmatites from the Araçuaí Orogen, further to the south. The εNdi can provide a further distinction for tracing Brazillian gemquality monazite reference materials.