Pattern of Sm-Nd TDM distribution in granulites and granitoids from an exposed section of middle to lower crust in se Brazil: Vertical and lateral zoning

Crustal accretion ages, as estimated through Sm-Nd TDM, can reveal limits between provinces or terranes and have been used in a continent scale to map the age structure of the Precambrian basement in North and South America (Nelson and DePaolo, 1985; Cordani and Sato, 1999). In favorable situations, Sm-Nd TDM observed in a given terrane varies within a limited range, and can thus be used to contrast it with neighboring terranes in terms of average crustal accretion ages. This may remain valid even for intrusive bodies inferred to derive from deep portions of the crust or mantle, showing the accretion ages to reflect a signature from the whole segment of continental lithosphere. Lithological and geochemical vertical zoning, however, is a feature of the continental crust, and the various magmatic, sedimentary and tectonic processes that are responsible for this differentiation can potentially produce important differences in Sm-Nd TDM among different levels of a given crust section. The present work investigates the vertical and lateral variation of Sm-Nd TDM in a tilted section of lower to middle crust exposed in an allochtonous terrane emplaced during the late Neoproterozoic at the SW border of the Sao Francisco Craton in SE Brazil. A significant spread of depleted-model ages is observed and correlated with portions of the terrane inferred to correspond to different paleodepths, implying vertical as well as lateral zoning of crustal accretion ages (au)