Aspectos petrológicos dos diques máficos de Itaju do Colônia e Floresta Azul: sul-sudeste do estado da Bahia, Brasil

Abstract

Research related to mafic dykes contributes to the understanding of the Earth’s dynamic, providing information about the composition and evolution of the mantle, distensive char-acteristics of the crust and, in some cases, associated mineralizations. The mafic dikes of Itaju do Colônia and Floresta Azul are part of the Província Litorânea and are located east of the São Francisco Craton. Field, petrography and geochemistry data indicate that: These mafic bodies are microgabbros with varied thicknesses ranging from centimetric to metric, from greyish-dark to greenish-gray, subvertical to vertical, and oriented NW-SE preferen-tial directions. It is also possible to identify the spheroidal exfoliation process in these rocks. Its main host rocks are mafic and intermediates polydeformed granulites from late archaean to paleoproterozoic. It is possible to identify the ophytic, subophytic, intergranu-lar, coronas and porphyritic textures. Plagioclase crystals have levels of anorthite varying from andesin to labradorite (An45-65), pyroxenes are predominantly augite and, rarely, hy-perstene, hornblende occur in corona texture around augita, opaque minerals and mica (biotite and chlorite) are characteristic of the rocks of these dykes. Sericitization and / or saussuritization and uralitization, occur in plagioclase and pyroxene, respectively. The dikes are chemically classified as subalcine jigs with toleitic tendency and tectonic envi-ronment according to the intraplate basalts. The amount of magnesium between 0.18 and 0.28 indicates basaltic magma evolved. Patterns of rare earth and multielementary charac-terize an enriched source between OIB and EMORB for a generation of these dikes locat-ed in this sector of the São Francisco Craton.