The Martín García Island (MGI, Buenos Aires Province, Argentina) is located in the Río de la Plata estuary, 44 km northeast of Buenos Aires city (Fig. 1). The aim of this work is to determine the chemical features and petrogenesis of the silicic rocks of the MGI. A selection of samples was made in order to analyse them petrographically and geochemically (bulk rock by ICP-MS).