Earth's new tectonic regime at the dawn of the Paleoproterozoic: Hf isotope evidence for efficient crustal growth and reworking in the São Francisco craton, Brazil

Abstract

Abstract A zircon Hf isotope data set from Archean and Paleoproterozoic magmatic and metasedimentary rocks of the southern São Francisco craton (Brazil) is interpreted as evidence of accretionary and collisional plate tectonics since at least the Archean-Proterozoic boundary. During the Phanerozoic, accretionary and collisional orogenies are considered the end members of different plate tectonic settings, both involving preexisting stable continental lithosphere and consumption of oceanic crust. However, mechanisms for the formation of continental crust during the Archean and Paleoproterozoic are still debated, with the addition of magmatic rocks to the crust being explained by different geodynamic models. Hf isotopes can be used to quantify the proportion of magmatic addition into the crust: positive εHf values are usually interpreted as indications of magmatic input from the mantle, whereas crust-derived rocks show more negative εHf. We show that the crust of the amalgamated Paleoproterozoic tectonostratigraphic terranes that make up the southern São Francisco craton were generated from different proportions of mantle and crustal isotopic reservoirs. Plate tectonic processes are implied by a consistent sequence of events involving (1) the generation of juvenile subduction-related magmatic arc rocks, followed by (2) collisional orogenesis and remelting of older crust, and (3) post-collisional bimodal magmatism.