CONICET | Buscador de Institutos y Recursos Humanos

In this study we present U?Pb and Hf isotope data combined with O isotopes in zircon from Neoarcheangranitoids and gneisses of the southern São Francisco craton in Brazil. The basement rocks record threedistinct magmatic events: Rio das Velhas I (2920?2850 Ma), Rio das Velhas II (2800?2760 Ma) and Mamona(2750?2680 Ma).The three sampledmetamorphic complexes (Bação, Bonfimand Belo Horizonte) have distinct εHf vs. time arrays,indicating that they grew as separate terranes. Paleoarchean crust is identified as a sourcewhich has been incorporatedinto younger magmatic rocks via melting and mixingwith younger juvenilematerial, assimilation and/orsource contamination processes. The continental crust in the southern São Francisco craton underwent a changein magmatic composition from medium- to high-K granitoids in the latest stages, indicating a progressive HFSEenrichment of the sources that underwent anatexis in the different stages and possibly shallowing of themeltingdepth. Oxygen isotope data shows a secular trend towards high δ18O (upto 7.79?) indicating the involvement ofmetasediments in the petrogenesis of the high potassium granitoids during the Mamona event. In addition, lowδ18O values (down to 2.50?) throughout the Meso- and Neoarchean emphasize the importance of meteoriticfluids in intra-crustal magmatism.We used hafnium isotope modelling from a compilation of detrital zircon compositions to constrain crustalgrowth rates and geodynamics from 3.50 to 2.65 Ga. The modelling points to a change in geodynamic processin the southern São Francisco craton at 2.9 Ga, from a regime dominated by net crustal growth in thePaleoarchean to a Neoarchean regime marked by crustal reworking. The reworking processes account for thewide variety of granitoid magmatism and are attributed to the onset of continental collision