Eventos igneos na Peninsula Fildes (Ilha Rei George) e no Pontal Fort (ilha greenwich), Islas Shetland do Sul – Antartica

Abstract

King George Island is located at the northeastern and Greenwich Island at the southwestern portions of the South Shetland Islands. 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 Peninsula are contemporaneous; (b) the intrusive rocks represent more evolved terms; (c) these rocks were originated from one single magmatic source and have undergone similar evolution processes and; (d) considering the available ages, these rocks were emplaced during Early Eocene.