Abstract
The meso-cenozoic alkaline magmatism in Rio de Janeiro is represented by several plutonic/volcanic bodies, which occurred on W-E fracture and lineaments zones associated with the development of the Southeastern Brazilian Rift. One of main occurrences of those rocks is the Itatiaia Alkaline Complex (IAC), which consists of nepheline-syentite, dykes of trachyte/phonolite and magmatic-hydrothermal breccia. This paper shows petrographic and mineralogical caracterization (optical petrography, SEM-EDS and XRD analysis) of breccia. The breccia comprises lithoclasts of trachyte and cristaloclasts of biotite and K-feldspar immersed in microcrystalline groundmass. As hydrothermal mineral it were observed albite, carbonate, sanidine, clinochlore, pyrite (also in lithoclasts), biotite, apatite, fluorite, tourmaline, sericite, synchysite (A parisite), Nb-rutilo, sphalerite, epidote and orthoclase (adularia?). Minerals associated to weathering are gibbsite, melanterita and cancrinite. The new occurrences of fluorcarbonates (synchysite and parisite) and Nb-rutile at the IAC, are rare minerals commonly associated with hydrothermal alteration in alkaline-carbonatite complexes. The hydrothermal paragenesis, as well as comparison with data from other alkaline associations of Rio de Janeiro, suggests that the study rocks consist in late-magmatic/hydrothermal autobreccia, associated to epithermal systems of low sulphidation subtype and generated during interaction with low-temperature alkalic fluids. The description of fluorite and REE-minerals at IAC opens the possibility to find those minerals in other alkaline complex of Rio de Janeiro.
Highlights
Caracterização Petrográfica e Mineralógica de Brechas Magmático-Hidrotermais no Complexo Alcalino de Itatiaia, Estado do Rio de Janeiro: Ocorrências de Fluorita e Minerais de ETR
This paper shows petrographic and mineralogical caracterization (optical petrography, SEM-EDS and XRD analysis) of breccia
Advances in geology of the porphyry copper deposits, southwestern north America
Summary
O Complexo Alcalino de Itatiaia (CAI) localiza-se no sul do estado do Rio de Janeiro, próximo à divisa dos Estados de São Paulo e Minas Gerais. Este se insere em um alinhamento W-E (Figura 1) de corpos plutônico-vulcânicos alcalinos cretáceo-cenozoicos no sudeste do Brasil, conhecido como Cadeia Poços de Caldas – Cabo Frio em sua porção continental e como Cadeia Vitória – Trindade em sua continuação oceânica (Thomaz Filho & Rodrigues, 1999). Ao analisarem e compilarem dados geocronológicos das rochas alcalinas do Estado do Rio de Janeiro, Thomaz Filho & Rodrigues (1999) observaram a tendência de idades decrescentes, de oeste para leste, desde o maciço de Poços de Caldas (MG) até o de Cabo Frio (RJ). Entretanto, Almeida (2006) defende a existência de zonas de fratura com direção W-E que serviriam como condutos facilitadores para a ascensão destes magmas, com extensão tanto ao longo da Cadeia Vitória – Trindade como no continente
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