Chapter IV: geochronology of the Jequié-Itabuna granulitic belt and of the Contendas-Mirante volcano-sedimentary belt

Voltas, Lagoa do Morro and Serra dos PombosArchean domes; and (iii) the determinations by Nutman, Cordani and Sabaté (in press) on one conglomerate sample from the Areião Formation (upper unit of the volcano-sedimentary sequence).The lack of higber resolution geochronological data as, for example, those produced by the different mono-zircon techniques, imposes restrictions to a finer-scale ordering of the regional geological events.Furthermore, despite the progress in the petrologic understanding of the region, difficu1ties still persist as to the identification of local heterogeneities, which, in turn, leads to uncertainty involving the cogenetic relations between samples used in the linear regressions ando as a resulto the real meaning of the age data obtained.TOE JEQUlÉ-ITABUNA GRANULITIC BELT This granulitic belt is divided here into the -Jequié-Mutuípe-Maracás Domain-and the -At1antic Coast Domain-, JEQUIÉ-MUTUiPE-MARACÁS DOMAIN This domain comprises "Plutonic Rocles equilibrated in Granulite Facies" and "011hoanil Paraderived Roeles MetomOTphosed in Granulite Facies" , .P1utoaic rocks equllibrated in graaulite fades These inc1ude the charno-enderbitic rocks from the Laje-Mutuípe region and the charnockitic rocks from the Maracás region, Chtuno-enderbitic roeles from the Laje-Mutulpe region Until late 1991 it was accepted that the geochronological evolution of tbis region followed the model proposed by Wilson (1987), This model was based on the followiDg data, ~ _rooa -..