U-Pb zircon and baddeleyite age and tectonic interpretation of the Itabuna alkaline suite, Sمo Francisco Craton, Brazil

Several stocks and batholiths comprise the Alkaline Province of Southern Bahia in the transition zone between the São Francisco Craton and the Neoproterozoic Araçuaí belt. One of these batholiths, the Itabuna syenitic suite, is located at the northeastern edge of the Itabuna shear zone and is intrusive into the Paleoproterozoic high grade rocks of the Itabuna belt. Two zircon and baddeleyite fractions from a pyroxene syenite of the Itabuna suite yield a U-Pb age of 676 ± 5 Ma. Additional whole rock Rb-Sr isochron ages reported for several alkaline bodies of the province fall in the range 660–570 Ma which may suggest that several pulses formed the Alkaline Province. 6 ± 5 Ma age of the Itabuna suite is similar to the age of main metamorphism and deformation in the Araçuaí belt. This similarity in age coupled with the emplacement of the alkaline plutonism in the area, controlled by fault zones, and the tectonic scenario that included deformation in the transition craton-fold belt zone (e.g., in the Rio Pardo basin) are all consistent with a relationship between the origin of the Alkaline Province and the crustal shortening related to the Araçuaí collision.