Recycling of the Archaean continental crust: the case study of the Gaviao,State of Bahia, NE Brazil

The Gaviao block, located to the west of the Sao Francisco Craton (State of Bahia, NE Brazil), is the oldest crustal block so far recognised in South America-3.42 Ga. In its southern part, the Gaviao block has been divided in to three domains on the basis of Pb-207/Pb-206 dating on single zircons and monazites combined with Sr and Nd isotopic data and major and trace elemen t geochemical modelling. These are: (1) an Archaean juvenile domain which c onsists of grey gneisses (Bernada massif) which evidence mantle extraction around 3.3 Ga; (2) an Archaean domain (3.24-3.16 Ga) either recycled, or ju venile with crustal contamination, consisting of trondhjemitic grey gneisse s (Aracatu massif) and K-rich calc-alkaline granitic gneisses (Mariana and Serra do Eixo massifs), (3) a Paleoproterozoic recycled domain consisting m ainly of the Umburanas granites, which yielded inherited zircons ages rangi ng from 3.1 to 2.8 Ga, whereas the monazite age is ca 2.0 Ga. The Aracatu a nd Mariana massifs are cut by granites at ca 2.0 Ga the same age of the Ser ra da Franga massif. The Gaviao block is a type example of Archaean contine ntal crust (3.2 Ga) that has been recycled through partial melting events m ainly in Paleoproterozoic times during the Transamazonian orogeny (2.0-2.1 Ga). Brasiliano cooling ages are recorded by the Rb-Sr system of biotite-wh ole rock pairs ca 500 Ma.(C) 1998 Elsevier Science Ltd. All rights reserved .