Abstract
The main lithological units which occur in the "Cabo Frio Tectonic Fragment" are orthogneisses and paragneisses. The orthogneisses have granitic-granodioritic-tonalitic compositions, with amphibolitic enclaves and intercalations and are cutted by granitic aplites. The paragneisses are metapelites, with intercalations of amphibolite, quartzites and calc-silicate rocks, metamorphosed in upper amphibolite facies, in intermediate pressure conditions. Geochemically, the orthogneisses correspond to a metaluminous high-K calc-alkalic series, with monzogabbro, quartz-monzodiorite and monzonite compositions. Otherwise, the petrography indicates a low-K calc-alkalic series, suggesting a pre-collisional granitoids series related to oceanic crust subduction. A divergence between the compositions obtained by the petrography and geochemistry can be the result of problems in the analyses of alkalies. The amphibolites, associated to the orthogneisses, also present calc-alkalic metaluminous character, with basaltic and andesitic compositions, suggestive of orogenic emplacement. The paragneisses show compositions varying between lithoarenite and arkoses, with peraluminous character, probably deposited in a continental are or ative continental margin environment.
Highlights
The main lithological units which occur in the "Cabo Frio Tectonic Fragment" are orthogneisses and paragneisses
As direções NNW observadas na região entre as cidades de Cabo Frio, Arraial do Cabo, Búzios e São Pedro da Aldeia contrastam com as direções NE-SW observadas regionalmente, pertencentes ao Cinturão Ribeira localizado ao longo da costa sudeste do Brasil
Com base nas publicações existentes, as rochas do "Fragmento Tectônico Cabo Frio" devem estender-se pelo menos alguns quilômetros para NW, incluindo parte das unidades denominadas por Reis et aI. como Unidades Tinguí-Maricá e Região dos Lagos
Summary
AMARAL, G.; BUSHEE, J. : CORDANI, U.G.; KAWASHITA, K. and REYNOLDS, J.H. Potassillm-argon dates ofalkaline rocks from SOllthem Brazil. FONSECA, A.C. Esboço geocronológico da região de Cabo Frio. Geologia estrutural da área de Cabo Frio e Armação de .Búzios. FONSECA, M.1 .G. O Cintur~o Ribeira e o Bloco Cabo Frio. : CHRISPIM, S.1.: ALVES, R.P. e SIMOES.L. S.A. Geologia do Cabo dos Búzios (Estado do Rio dc Janeiro) An. Acad. ROSIER, G.F, Pesquisas geológicas na parte oriental do Estado do Rio de Janeiro e na parte vizinha do Estado de Minas Gerais, Brasil, DNPM-DGM, boI. A. and LE MAITRE, R W, A chemical approximation to the modal QAPF c1assification of the igneous rocks, N.Jb, Mineral. ; KA WASHITA, K. e VAN SCHUMS, W.R, Evidências de um núcleo transamazônico na região de Cabo Frio, RJ, e sua correlação com o Cráton de Angola, África, An, XXXVI Congr. Geo!.: 2735-2743 , 1990, TABELAl.l - Análise modal de alguns ortognaisses e anfibolitos da área
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