New U-Pb SHRIMP-II zircon intrusion ages of the Cana Brava and Barro Alto layered complexes, central Brazil: constraints on the genesis and evolution of the Tonian Goias Stratiform Complex

Abstract

The Cana Brava, Niquelândia and Barro Alto complexes (Goiás, central Brazil) are three of the largest mafic-ultramafic layered complexes in the world and their origin has been a matter of debate for several decades. One hypothesis suggests that Niquelândia and Barro Alto were both formed by two distinct igneous events at 1.3 Ga and at 790Ma and were later overlapped during tectonic exhumation at 650 Ma; according to this reconstruction Cana Brava belongs to the youngest intrusion at 790 Ma. A second hypothesis suggests that the three complexes formed during the same event. Here we provide new U-Pb SHRIMP-II zircon ages for the Cana Brava and Barro Alto complexes, constraining their intrusion age to the Neoproterozoic (between 770 and 800 Ma), coeval with Niquelândia. A review of new and literature ages indicate that these complexes formed during a single igneous event andwere notmodified by regional metamorphism.We propose that the complexes represent fragments of the larger Tonian Goiás Stratiform Complex, which was likely part of a back-arc environment connected to the formation of the GoiásMagmatic Arc at about 790Ma, later disrupted and accreted to the São Francisco craton

The Influence of the Magmatic to Postmagmatic Evolution of the Parent Rock on the Co Deportment in Lateritic Systems: The Example of the Santa Fé Ni-Co Deposit (Brazil)

“…The Tonian Goiás Stratiform Complex is located in the northeastern sector of the Goiás State and is considered one of the biggest mafic to ultramafic complexes worldwide. The emplacement of the Tonian Goiás Stratiform Complex is believed to be Mesoproterozoic to Neoproterozoic in age (800-770 Ma; Pimentel et al, 2000;Giovanardi et al, 2017), although its geodynamic setting is still a matter of debate. Many authors (e.g., Pimentel et al, 2004Pimentel et al, , 2006Giovanardi et al, 2017) suggested that continental rift and back-arc extension in continental crust settings are the most appropriate geodynamic scenarios for the Tonian Goiás Stratiform Complex emplacement.…”

Isotopic constraints on contamination processes in the Tonian Goiás Stratiform Complex

“…4 samples from Cana Brava, 3 from Barro Alto and 3 from Niquelândia were selected for analyses in zircons of the Lu-Hf and U-Pb isotope systematics. Some of these samples were already investigated for U-Pb analysis (Correia et al, 2007(Correia et al, , 2012Giovanardi et al, 2015Giovanardi et al, , 2017b. When possible, Lu-Hf analyses were carried out onto the same crystals and domains analyzed for U-Pb.…”

“…2). U-Pb SHRIMP ages from the three samples were discussed in Giovanardi et al (2017b). Samples CB1175 and CB1382 are hydrous granoblastic gabbros with foliation parallel to the complex direction derived by the alignment of pyroxenes and plagioclases.…”

“…While the LS is formed by ultramafics and gabbros showing increasing crustal contamination along the stratigraphy (Correia et al, 1997(Correia et al, , 2012Rivalenti et al, 2008;Giovanardi et al, 2017a), the US consists of anorthosites and olivine-gabbros and is considered uncontaminated (Rivalenti et al, 2008;Correia et al, 2012). This difference between the two units has generated two opposite models of formation: the two-intrusions model, where the LS and US are considered separated intrusions of Neoproterozoic and Mesoproterozoic ages, respectively (Pimentel et al, 2004(Pimentel et al, , 2006Ferreira Filho et al, 2010;Della Giustina et al, 2011) and the one-intrusion model, in which the US crystallized from an anorthositic melt segregated from the precipitation of the LS ultramafics (Rivalenti et al, 2008;Correia et al, 2012;Giovanardi et al, 2017b).…”

“…Therefore, new Lu-Hf isotopic analyses of zircons were carried out to constrain the contamination of LS and US in the three fragments of the TGSC. Analyses were also performed on previously SHRIMP U-Pb dated zircons from Giovanardi et al (2017b) and Correia et al (2007Correia et al ( , 2012.…”