São Francisco–Congo Craton break-up delimited by U–Pb–Hf isotopes and trace-elements of zircon from metasediments of the Araçuaí Belt.

Abstract

Detrital zircon U–Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Araçuaí Belt in southeastern Brazil provide evidence for break-up of the Congo–São Francisco Craton. The U–Pb age spectra of detrital zircons from metasediments of the Rio Doce Group (RDG) range from 900–650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon εHf(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Araçuaí Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Araçuaí Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.