The Tiger Gabbro from northern Victoria Land, Antarctica: the roots of an island arc within the early Palaeozoic margin of Gondwana
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The Tiger Gabbro layered intrusion is one of the few mafic intrusive bodies found along the ancient Antarctic Gondwana margin. Major and trace element data and Sr–Nd isotope compositions for gabbronorites indicate an island arc signature for the Tiger Gabbro parental magma. This is the first evidence for an island arc from plutonic rocks in northern Victoria Land. The interpretation of the Tiger Gabbro as the roots of an Early Cambrian island arc (535 ± 21 Ma, Sm–Nd age), integrated with geochemical and geochronological data from the literature, matches the occurrence of the Glasgow volcanic rocks in the southern Bowers terrane, which possibly represents its effusive counterpart. A scenario for the early Palaeozoic Antarctic Gondwana margin is hence proposed in which the Tiger volcanic arc developed on the Robertson Bay microplate in response to subduction of the palaeo-Pacific plate. The Tiger arc igneous activity was coeval to the Wilson continental arc (represented by the Granite Harbour intrusive rocks), with the two subduction zones merging southwards into one. The migration of the Wilson arc towards the forearc region in turn generated the Middle Cambrian Bowers arc.