Geoquímica e geocronologia (U-Pb e Lu-Hf) das intrusões alcalinas félsicas de Soarinho, Tanguá, Rio Bonito e Tinguá: implicações sobre as fontes do magmatismo alcalino no Estado do Rio de Janeiro

• Autor(a) principal: Silva, Daniel Adelino da
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/6995
• topic: Felsic alkaline rocks; Geochemistry; U-Pb ages; Hf Isotopes; Crustal assimilation; Rochas alcalinas félsicas; Geoquímica; Idades U-Pb; Isótopos de Hf; Contribuição crustal; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

This thesis investigates the Cretaceous Soarinho, Tanguá, Rio Bonito, and Tinguá alkaline intrusions which form part of the South-eastern Brazilian Alkaline Province or Poços de Caldas-Cabo Frio Magmatic Lineament. Petrographic, geochemical, geochronological (U-Pb), and isotopic (Lu-Hf) studies were undertaken of the intrusive bodies. The Tanguá, Rio Bonito and Tinguá intrusions are composed of mostly nepheline syenite cut by phonolite dykes, with isolated outcrops of mafic and intermediate rocks. In contrast, the Soarinho intrusion consists of monzonite, alkali feldspar syenite, alkali feldspar trachyte and quartz syenite. Geochemically Tanguá, Rio Bonito and Tinguá are mainly metaluminous and plot within the ultra potassic and potassic fields, while Soarinho is mainly peraluminous and potassic. The geochemical data indicate an evolution by AFC for the Tanguá and Rio Bonito intrusions. However, magma mixing is suggested for the Soarinho intrusion with mixing between a monzonite magma (36% to 44%) and an alkali feldspar syenite magma (56% to 64%) resulting in an overall quartz syenite composition. Zircon U-Pb Laser Ablation ages show that the nepheline syenites of both the Tanguá and Rio Bonito intrusions are contemporaneous (65 Ma), with a similar age (66 Ma - within error) obtained for nepheline syenites from Tinguá. On the other hand, dating of Soarinho show that it is the youngest (58 Ma) of the studied intrusions, with the ages obtained from the monzonite, alkali feldspar syenite and quartz syenite, indistinguishable (within error). The magma mixing model suggest that at least three magmatic pulses were responsible for the formation of the Soarinho intrusion: the first pulse related to the monzonite and the two subsequent pulses leading to the emplacement of the alkali feldspar syenite and quartz syenite. The εHf values of all the samples from intrusions are negative with average values of -8 for Soarinho, -11 for Tanguá, -14 for Rio Bonito and -12 for Tinguá. This isotopic signature and the geochemistry data of the alkaline rocks point to an enriched mantle source with a negative εHf value. However, assimilation by an older continental crust source can not be ruled out for the formation of the alkaline rocks of this Province