Juvenile, mantle-derived complexes are relatively rare in the late Neoproterozoic Brasiliano orogenic belts of western Gondwana, which consist primarily of reworked older crust. The Vila Nova belt in the São Gabriel block of the southern Mantiqueira province, southern Brazil, consists of granodioritic to tonalitic gneisses (Cambaí group) and deformed basaltic to rhyolitic volcanic rocks and sedimentary rocks (Vacacaí supergroup). U-Pb zircon data show that plutonic and volcanic rocks of both groups formed between 750 and 700 Ma. Sm-Nd model ages range from 1000 to 800 Ma with positive ϵNd(t) values, identifying the Vila Nova belt as a juvenile terrane. We postulate that 1000–800 Ma oceanic crust was subducted eastward below a Transamazonian (2100 Ma) craton; this process formed supracrustal rocks of the Vacacaí supergroup and plutons and supracrustal rocks of the Cambaí group and caused associated deformation. This juvenile terrane represents another tectonic marker for defining the earlier stages of western Gondwana assembly.