ISOTOPIC SIGNATURES OF PALEOPROTEROZOIC GRANITOIDS OF THE GAVIÃO BLOCK AND IMPLICATIONS FOR THE EVOLUTION OF THE SÃO FRANCISCO CRATON, BAHIA, BRAZIL

Intense granitic plutonism of peraluminous and metaluminous calc-alkaline affinity took place in the northern sector of the São Francisco Craton, during the Paleoproterozoic. Rb-Sr and 207 Pb/ 206 Pb(zircon) radiometric data for the granitoids yield crystallization ages at ca. 2.0 Ga. The calculated 87 Sr/ 86 Sr initial ratios (up to 0.727), T DM model ages (between 2.6 and 3.5 Ga) and the range in the e Nd(t) values (- 5.8 to –13.4) are all compatible with participation of variable proportions of Archean crust material in the magma genesis of such plutons. Tectonically, these granites originated due to the Transamazonian collisional orogeny, which developed within large terranes of the Craton along the edge of the Archean Gavião Block.