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
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A zircon Hf isotopes dataset of Archean and Paleoproterozoic magmatic and metasedimentary rocks of southern São Francisco Craton is interpreted as evidence of accretionary and collisional plate tectonics at least since the Archean-Proterozoic boundary. During the Phanerozoic, accretionary and collisional orogenies are considered the end members of different plate tectonic settings, both involving pre-existing 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 ɛHf values are usually interpreted as indications of magmatic input from the mantle, whereas crust-derived rocks show more negative ɛHf. 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 the generation of juvenile subduction-related magmatic arc rocks, followed by collisional orogenesis and re-melting of older crust, and post-collisional bimodal magmatism.