The Pan-African/Brasiliano Orogeny in South America comprises a series of late Neoproterozoic to Cambrian mobile belts that formed during the assembly of West Gondwana (e.g., Trompette, 1994). The belts are broadly coeval in their development, and tectonic aspects. Nevertheless, they are not completely simultaneous; hence structural and tectonic interferences related to either thrusting or transpression exist where they intersect each other. One well-exposed case of tectonic interaction is in southeastern Brazil where the Ribeira belt transects the Brasília belt, in the southern margin of the São Francisco Craton. The interaction between these two mobile belts during the Brasiliano Orogeny generated a complex array of structures (e.g., Ribeiro et al., 1995; Ebert and Hasui, 1998; Hackspacher and Godoy, 1999; Campos Neto and Caby, 1999; Heilbron and Machado, 2003; Valeriano et al., 2004). It is generally accepted that the final collision of the Ribeira belt was later than that of the southern Brasília belt (Hasui et al., 1990; Trouw et al., 2000; Campos Neto and Figueiredo, 1995). However, to what degree the transpressional regime of the Ribeira belt overprinted the Brasília belt rocks remains weakly constrained.
Accurate and precise radiometric ages are necessary to reconstruct the Brasiliano Orogeny and to better understand the regional geologic framework and major structural features of each belt. In order to correlate geologic, structural and geochronologic features of the interference zone, we present new U-Pb monazite and 40Ar/39Ar mica data from selected granitoids, pegmatites, paragneisses and schists that crop out in the intersection between the Brasília belt and central part of the Ribeira belt. These data provide the first detailed age constraints on the late stage of metamorphism, uplift and cooling of the southern Brasília belt, and reveal the thermal and structural overprint of the Ribeira belt collision that led to assembly of West Gondwana.