An igneous event at the Fildes Peninsula (King George Island) and around fort point (greenwich island), south shetland islands, Antarctica

• Main Authors: Almeida, Delia Del Pilar Montecinos de, Machado, Adriane, Hansen, Marco Antônio Fontoura, Jr., Farid Chemale, Fensterseifer, Henrique Carlos, Petry, Karla, Lima, Larissa de
• Format: Article in Journal/Newspaper
• Language: Portuguese
• Published: Zeppelini Editorial 2003
• Subjects: Antarctica; magmatism; geochemistry; tectonic environment; Antártica; magmatismo; geoquímica; ambiente tectônico; Fildes; Fildes peninsula; Fort Point; Greenwich; Greenwich Island; King George Island; Nordeste; South Shetland Islands; Antarc*; Antarctica; antartic*; Antártica
• Online Access: http://revistas.ufpr.br/rbg/article/view/10250; https://doi.org/10.5380/rbg.v33i4.10250

King George Island is located at the northeastern and Greenwich Island at the southwestern portions of the South ShetlandIslands. The studied volcanic suits were emplaced as flows and subvolcanics of basaltic-andesitic and andesitic compositions. The intrusive rocks display dioritic to granitic compositions. Geochemical patterns indicate the geochemical similarity of the rocks and that the volcanism preceded the plutonism. Incompatible trace element behavior shows a calc-alkaline affinity and that these rocks were generated in a subduction zone. Large negative Ta, Ti, P and Nb anomalies, typical of an island-arc environment, are also observed. The initial Sr87/Sr86 ratios and the positive eNd suggest derivation from a mantle source with little or no assimilation of continental crust. Pb isotopic ratios attest to the isotopic similarity of all the rocks. Based on petrographic, geochemical and isotopic data, it is concluded that: (a) the volcanic rocks from Fort Point and the Fildes Península are contemporaneous; (b) the intrusive rocks represent more evolved terms; (c) these rocks were originated from one single magmatic source and have undergone similar evolutionprocesses and; (d) considering the available ages, these rocks were emplaced during Early Eocene. As ilhas estudadas fazem parte do arquipélago Shetland do Sul, com a ilha Rei George a nordeste e a ilha Greenwich na parte central do arquipélago. As suítes vulcânicas estudadas se manifestam como derrames e de maneira sub vulcânica, de composições basáltico-andesítica e andesítica. As rochas intrusivas variam de composição diorítica a granítica. Os padrões geoquímicos indicam a similaridade geoquímica de todas as rochas e que o vulcanismo precedeu o plutonismo. O comportamento dos elementos traço incompatíveis mostra a afinidade cálcio-alcalina de todas as rochas e sua geração em zonas de subdução. Anomalias negativas de Ta, Ti, P e Nb, típicas de arcos de ilhas, também são observadas. As razões iniciais Sr87/Sr86 e os valores positivos de eNd sugerem origem mantélica do(s) magma(s), com pouca ou nenhuma assimilação de crosta continental. As razões isotópicas de Pb atestam a similaridade isotópica entre todas as rochas. Com base nos resultados petrográficos, geoquímicos e isotópicos, conclui-se que: (a) as rochas vulcânicas do Pontal Fort e Peninsula Fildes são contemporâneas; (b) as rochas intrusivas representam termos mais evoluídos; (c) estas rochas se originaram a partir de uma única fonte magmática e sofreram processos de evolução similares e; (d) considerando as idades existentes, estas rochas posicionaram-se durante o Eoceno inferior.