Isotopic signatures of Paleoproterozoic granitoids from the southern Sao Francisco Craton and implications for the evolution of the Transamazonian Orogeny

The southern Sao Francisco Craton: northeastern Brazil, consists of an Archean block surrounded by a Paleoproterozoic bell related to the Transamazonian Orogeny (ca. 2.0 Ga). A calc-alkaline plutonic are developed within the belt and the granitoid plutons comprise two distinct groups. One group displays Archean T-DM ages (3.07-2.62 Ga), epsilon(Nd(t)) values between -11.0 and -3.8 and high initial Sr-87/Sr-86 values, and it consists mainly of peraluminous granites. TDM ages for the other group are Paleoproterozoic (2.33-2.27 Ga), and epsilon(Nd(t)) values range between -2.8 and +1.3; the plutons are metaluminous tonalites (trondhjemites) to granodiorites, The Transamazonian granitoids can be related to contrasting source-regions, from mantle- to crust-derived ones. A number of them are probably derived from mixing of Paleoproterozoic juvenile material and variable proportions of Archean crust material. Magmatism related to deep faulting, during the compressional stages of the Transamazonian Orogeny, is a plausible model for granitoid generation. The contribution of mantle-derived material to the granitoid sources supports the idea that a significant episode of new crust formation occurred during the Transamazonian Orogeny. (C) 2000 Elsevier Science Ltd. All rights reserved.