JUVENILE ACCRETION AT 750-700 MA IN SOUTHERN BRAZIL

Juvenile, mantle-derived complexes are relatively rare in the late Neo proterozoic Brasiliano orogenic belts of western Gondwana, which consi st primarily of reworked older crust, The Vila Nova belt in the Sao Ga briel block of the southern Mantiqueira province, southern Brazil, con sists of granodioritic to tonalitic gneisses (Cambai group) and deform ed basaltic to rhyolitic volcanic rocks and sedimentary rocks (Vacacai supergroup), U-Pb zircon data show that plutonic and volcanic rocks o f both groups formed between 750 and 700 Ma. Sm-Nd model ages range fr om 1000 to 800 Ma with positive epsilon(Nd)(t) values, identifying the Vila Nova belt as a juvenile terrane, We postulate that 1000-800 Ma o ceanic crust was subducted eastward below a Transamazonian (2100 Ma) c raton; this process formed supracrustal rocks of the Vacacai supergrou p and plutons and supracrustal rocks of the Cambai group and caused as sociated deformation, This juvenile terrane represents another tectoni c marker for defining the earlier stages of western Gondwana assembly.