Browsing by Author "Medeiros Junior, Edgar Batista de"

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    Petrografia e termobarometria de granitoides diatexíticos portadores de anfibólio da região de São José de Ubá e São João do Paraíso (RJ).
    (2020) Ferreira, Sandro Lúcio Mauri; Marques, Rodson de Abreu; Melo, Marilane Gonzaga de; Medeiros Junior, Edgar Batista de; Reis, Sâmara Veiga dos; Silva, Roger Mendes; Valle, Heitor de Freitas; Queiroga, Gláucia Nascimento
    Na região norte do Rio de Janeiro afloram rochas orto e paraderivadas neoproterozoicas de alto grau metamórfico, englobadas no Terreno Oriental da Faixa Ribeira. Dado a carência de estudos de detalhe na região, o presente trabalho contribui com novos aspectos de campo, petrografia, química mineral e geotermobarometria dos granitoides diatexíticos aflorantes na região entre São José de Ubá e São João do Paraíso, no noroeste fluminense. O litotipo é caracterizado por biotita-hornblenda gnaisses migmatíticos e protomiloníticos que são correlacionáveis a ortognaisses e granulitos do Complexo Serra da Bolívia (Domínio Cambuci da Faixa Ribeira). Dois litotipos neoformados são observados: um mesocrático, de caráter residual; e outro leucocrático, que correspondente ao leucossoma. O enriquecimento de K-feldspato no leucossoma em relação ao neossoma residual sugere baixos volumes de fusão por meio de reações de fusão envolvendo água. Aplicando-se diferentes geotermobarômetros, foram obtidas como condições de equilíbrio para o pico metamórfico 6,8 Kbar e 672–680°C (fácies anfibolito superior). Tais valores destoam dos encontrados na literatura para ouras rochas da região, reforçando a ideia de que os domínios do Terreno Oriental da Faixa Ribeira apresentam evoluções metamórficas distintas, em diferentes níveis crustais.
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    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.