U-PB ZIRCON AND BADDELEYITE AGE AND TECTONIC INTERPRETATION OF THE ITABUNA ALKALINE SUITE, SAO-FRANCISCO CRATON, BRAZIL

Several stocks and batholiths comprise the Alkaline Province of Southe rn Bahia in the transition zone between the Sao Francisco Craton and t he Neoproterozoic Aracuai belt. One of these batholiths, the Itabuna s yenitic suite, is located at the northeastern edge of the Itabuna shea r 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. Additi onal whole rock Rb-Sr isochron ages reported for several alkaline bodi es of the province fall in the range 660-570 Ma which may suggest that several pulses formed the Alkaline Province. The 676 +/- 5 Ma age of the Itabuna suite is similar to the age of main metamorphism and defor mation in the Aracuai belt. This similarity in age coupled with the em placement of the alkaline plutonism in the area, controlled by fault z ones, and the tectonic scenario that included deformation in the trans ition craton-fold belt zone (e.g., in the Rio Pardo basin) are all con sistent with a relationship between the origin of the Alkaline Provinc e and the crustal shortening related to the Aracuai collision. (C) 199 7 Published by Elsevier Science Ltd.