Relacoes tectonicas das rochas alcalinas mesozoicas da regiao meridional da plataforma sul-americana

The tectonic setting of Upper Jurassic to Eocene alkaline rocks south of the 15oS parallel, in Brazil, Bolivia, Paraguay and Uruguay is reviewed and its proposed relationships with plate tectonics are discussed. More than one hundred occurrences of intrusive and extrusive rocks are recognized, which are tentatively grouped in twelve alkaline provinces, disposed around the borders of the Parana Basin, the continental border near the Santos Basin and the cratonic interior of Bolivia. Silica saturated to supersaturated felsic alkaline rocks are frequently found in provinces located far from the Parana Basin. The importance of the control of arches. flexures, rifts and deep faults over the magmatic phenomena is stressed.