Itabuna

Itabuna comprises a complex of syenite, diorite, monzodiorite and granite, with associated dykes, of approximately 18x40 km, intruding a broad range of Precambrian granulite facies rocks, but is overlapped on its eastern margin by Mesozoic sediments. Syenites, the most abundant rock type, include a range of pyroxene-, amphibole- and biotite-bearing types, the feldspars varying between perthite, microcline and sodic plagioclase. The pyroxenes vary from Ti-augite to aegirine-augite. The amphiboles are principally arfvedsonite but hornblende and katophorite also occur; the biotite is Ti-rich. The diorites and monzodiorites consist of oligoclase, perthite, Ti-biotite, hornblende and accessories. Granites are relatively minor and it is not clear from descriptions if they are peralkaline. A varied suite of dykes occur within the complex and cutting the surrounding granulites and include alkali basalts, (?)nephelinites, phonolites, trachytes and syenitic aplites. The trachytes contain biotite and a sodic amphibole. The so-called nephelinites comprise poikilitic kaersutite, nepheline, plagioclase, carbonate and opaques. The chemistry of the rocks, most of which are nepheline-normative and miaskitic, is described and discussed by Oliveira et al. (1980).