U-Pb geochronology and Sr-Nd isotopes of Galileia and Urucum Neoproterozoic granitoids suites in south-eastern Brazil.

U-Pb zircon and monazite dating and whole-rock Sr-Nd isotopes have been app lied on Neoproterozoic granitoids from the Atlantic sheer belt, south-easte rn Brazil. U-Pb zircon results on the Galileia metaluminous and Urucum pera luminous suites indicate crystallisation ages of 594 +/- 6 Ma and 582 +/- 2 Ma respectively. Whole-rock Rb-Sr and Sm-Nd analyses on representative sam ples from both suites demonstrate that they mainly derive from melting of o lder crustal rocks. The occurrence of an old isotopic memory in the zircons from the Urucum granitoids around 2.2 Ga, in agreement with Nd model ages, suggests a Palaeoproterozoic age for the crustal protolith of these two su ites, probably associated with the Transamazonico event. Owing to these new dating results and previous regional geochronological data, it can be prop osed that the metaluminous magmatism ended around 590 Ma and that the colli sional peraluminous magmatism associated with the Brasiliano orogeny occurr ed between 584 and 570 Ma. (C) 2000 Academie des sciences/ Editions scienti fiques et medicales Elsevier SAS.