| Summary: | Bertrab Nunatak is located in the Vahsel Bay area, Weddell Sea, Antarctica. It is composed of a granitic body, «Granito Bertrab», cut by acid aplite/rhyolite and quartz veins) and basic dyke-swarms. Granito Bertrab is a coarse-grained, granophyric quartz-feldspar biotite granite with minor normative corundum (1%) that indicates peraluminous affinities. Melanocratic calc-alkaline dykes, with labradorite-andesine and amphibole megacrysts, have a lamprophyric character. One of these is cut by a leucocratic dike, that represents the final stage in the magmatic activity. Petrological evidence indicates that there is a temporally, spatially and genetically intimate association bewteen the granite and the dykes. K-Ar data on samples of the granite give an age of 996 ± 40 Ma, and the Rb-Sr isochron age recalculated using the published data of Eastin and Faure give an age of 971 ± 8 Ma using five samples, and 992 ± 12 Ma when the aplitic member is not included. These results are in good agreement with the K-Ar age and mean that the Granito Bertrab was emplaced in the late Mesoproterozoic. Fil: Acevedo, Rogelio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Linares, Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Alberdi Valin, Maria Luz. Universidad de Oviedo; España Fil: Ostera, Hector Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Martín Izard, Agustín. Universidad de Oviedo; España
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