THE NEOPROTEROZOIC GOIÁS MAGMATIC ARC, CENTRAL BRAZIL: A REVIEW AND NEW Sm-Nd ISOTOPIC DATA

Abstract

In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goiás Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenópolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvânia area yielded a Sm-Nd whole-rock isochron age of 863 ± 97 Ma and e Nd (T) of +4.1. T DM model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole-rock isochron age of 762 ± 77 Ma and e Nd (T) of +2.9. T DM values are between 0.96 and 1.10 Ga. In the northern section of the Goiás Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 ± 120 Ma and initial e Nd value of ca. +2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaean terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustals, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the São Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia supercontinent.