THE GEOLOGY OF CAPE-DUBOUZET, NORTHERN ANTARCTIC PENINSULA - CONTINENTAL BASEMENT TO THE TRINITY PENINSULA GROUP

Cape Dubouzet is mainly composed of a volcanic-subvolcanic complex of extrusive rhyolitic breccias, a banded rhyolite and a semi-annular bod y of dacite porphyry rich in xenoliths of metamorphic rocks. Major and REE geochemistry indicate that the volcanic rocks are calc-alkaline a nd that they are genetically related by fractional crystallization of a plagioclase-bearing assemblage from a common magma. Rb-Sr data sugge st that the rhyolitic complex is of Middle-to-Late Jurassic age, and t hat it is intruded by Late Cretaceous stocks of banded diorite and gab bro. All these rocks are partially covered by moraines whose clasts ar e of local provenance. Xenoliths in the dacite porphyry suggest that t he northern tip of the Antarctic Peninsula is underlain by a metamorph ic complex composed of amphibolites, meta-tonalites and pelitic gneiss containing garnet, sillimanite, cordierite, hercynite, and andalucite . Such rocks are not known in the Scotia metamorphic complex, nor in t he Trinity Peninsula Group and its low grade metamorphic derivatives, which also occur as rare xenoliths in the dacite. Previous dating of x enoliths collected from the moraines suggested a late Carboniferous ag e for this amphibolite-grade metamorphism. Both the Jurassic-Cenozoic magmatic are of the Antarctic Peninsula and the accretionary complex r ocks of the Trinity Peninsula Group were thus developed, at least in p art, over pre-existing continental crust.