Mineralogical, petrological and geochemical aspects of alkaline and alkaline-carbonatite associations from Brazil

A general description of Mesozoic and Tertiary (Fortaleza) Brazilian alkaline and alkaline-carbonatite districts is presented with reference to mineralogy, petrology, geochemistry and geochronology. It mainly refers to scientific results obtained during the last decade by an Italo-Brazilian research team. ne occurrences are distributed across Brazilian territory from the southern (Piratini, Rio Grande do Sul State) to the northeastern (Fortaleza, Cearل State) regions and are mainly concentrated along the borders of the Paranل Basin generally coinciding with important tectonic lineaments. st noteworthy characteristics of these alkaline and alkaline-carbonatite suites are: (i) prevalence of intrusive forms; (ii) abundance of cumulate assemblages (minor dunites, frequent clinopyroxenites and members of the ijolite series) and (iii) abundance of evolved rock-types. ata demonstrate that crystal fractionation was the main process responsible for magma evolution of all Brazilian alkaline rocks. thesis is proposed for the genesis of carbonatite liquids by immiscibility processes. cidence of REE and trace elements for different major groups of lithotypes, belonging both to carbonatite-bearing and carbonatite-free districts, are documented. preliminary Nd isotopic data are indicative of a mantle origin for the least evolved magmas of all the studied occurrences. source material and melting models for the generation of the Brazilian alkaline magma types are also discussed.