Multiple processes of geochemical evolution for the alkaline rocks of Rio Bonito intrusive complex, Rio de Janeiro State, Brazil: <superscript>40</superscript>Ar/<superscript>39</superscript>Ar and U-Pb ages and Lu-Hf isotopes on zircon and constraints on crustal signature. - OpacWWW

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Tytuł:: Multiple processes of geochemical evolution for the alkaline rocks of Rio Bonito intrusive complex, Rio de Janeiro State, Brazil: Ar and U-Pb ages and Lu-Hf isotopes on zircon and constraints on crustal signature.
Autorzy:: Adelino da Silva, Daniel
Motoki, Akihisa
Costa dos Santos, Anderson
Mendes, Julio
Jourdan, Fred
César Geraldes, Mauro
de Carvalho Lana, Cristiano
Temat:: ANALYTICAL geochemistry
RARE earth metals
ALKALINE earth compounds
SPHENE
ZIRCON
ISOTOPES
Alternatywny tytuł:: Múltiplos processos de evolução geoquímica para as rochas alcalinas do complexo intrusivo de Rio Bonito, Estado do Rio de Janeiro, Brasil: idades Ar e U-Pb e isótopos Lu-Hf em zircão - considerações sobre assinatura crustal (Portuguese)
Źródło:: Geologia USP: Série Científica; dez2020, Vol. 20 Issue 4, p213-234, 22p
Abstract (English):: This article presents geochemical characteristics of the alkaline rocks of Rio Bonito intrusive complex, State of Rio de Janeiro, Brazil, which is constituted mainly by nepheline syenite. The fractional crystallisation of this magma decreases K2O/(Na2O + K2O) and increases (Na + K)/Al. The TiO2, Fe2O3*, MgO, CaO, and P2O5 contents indicate fractionation of titanite, ilmenite, and clinopyroxene or amphibole. The total rare earth elements (REEs) are high, and the REE pattern is linear with negative gradient. The nepheline syenite aplite has low REEs, concave REE pattern, and positive Eu anomaly. The ultrabasic and basic mela-nepheline syenite samples have total REEs and light REEs higher than the felsic alkaline rocks. Therefore, the nepheline syenite magma is not derived directly from the alkaline ultrabasic magma. Laser-spot step-heating Ar ages for biotite and amphibole are 65.03 ± 0.70 and 65.03 ± 0.46. U-Pb ages LA-ICP-MS for two samples are 65.49 ± 0.30 and 65.18 ± 0.30. Values of eHf are negative for both samples, indicating an important crustal component in the evolution of Rio Bonito. [ABSTRACT FROM AUTHOR]
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Multiple processes of geochemical evolution for the alkaline rocks of Rio Bonito intrusive complex, Rio de Janeiro State, Brazil: 40Ar/39Ar and U-Pb ages and Lu-Hf isotopes on zircon and constraints on crustal signature.