Géochronologie U-Pb et géochimie isotopique Sr-Nd des granitoïdes néoprotérozoïques des suites Galiléia et Urucum, vallée du Rio Doce, Sud-Est du Brésil = U-Pb geochronology and Sr-Nd isotopes of Galiléia and Urucum Neoproterozoic granitoids suites in south-eastern Brazil
Résumé
Kesnact S Tb geocinonology and St-Nd isotopes of Ganicia and Grachnn Ncoproterozoic granitoids suites in south-eastern Brazil. U-Pb zircon and monazite dating and whole-rock Sr-Nd isotopes have been applied on Neoproterozoic granitoids from the Atlantic shear belt, south-eastern Brazil. U-Pb zircon results on the Galiléia metaluminous and Urucum peraluminous suites indicate crystallisation ages of 594 ± 6 Ma and 582 ± 2 Ma respectively. Whole-rock Rb-Sr and Sm-Nd analyses on representative samples from both suites demonstrate that they mainly derive from melting of older 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 suites, probably associated with the Transamazônico event. Owing to these new dating results and previous regional geochronological data, it can lie proposed that the metaluminous magmatism ended around 590 Ma and that the collisional peraluminous magmatism associated with the Brasiliano progeny occurred between 584 and 570 Ma.
Mots clés
granitoids
upper Proterozoic
Brazil
dating
U/Pb
zircon
monazite
Sr-87/Sr-86
Nd-144/Nd-143
isotope geochemistry
whole rock
anatexis
petrogenesis
protoliths
lower Proterozoic
peraluminous composition
tectonic setting
plutonic rocks
igneous rocks
Proterozoic
Precambrian
South America
nesosilicates
silicates
phosphates