Age and mantle source characteristics of kimberlite-derived zircons from Brazil revealed by U–Pb, Hf and O isotopes

We report new U–Pb, Hf and O isotope data for zircon megacrysts from three kimberlites and diamondiferous areas in Brazil: Juína and Paranatinga kimberlite fields (Amazonian craton) and the Alto Paranaíba Igneous Province (APIP, São Francisco craton). A total of 253 mantle-derived zircon grains from kimberlites, diamondiferous streams, and diamond mines were analysed. Our U–Pb age data indicates four main age peaks for zircon that suggest kimberlite magmatism: ca. 78 and 86 Ma in APIP, 92 Ma in Juína, and 122 Ma in Paranatinga. Zircon Hf isotope signatures vary systematically with location: Juína and Paranatinga εHf_i values are + 4.2 to + 9.3; APIP range from − 11.0 to 0.0. There is minimal variability in zircon oxygen isotopes, most falling within 2SD (standard deviation) of the range for typical mantle zircons (5.3 ± 0.6‰). Zircons from Juína and Paranatinga have lower δ¹⁸O values (+ 5.12 to + 5.07‰) than those from APIP (+ 5.38‰). The contrasting Hf and O isotope compositions between zircons from the Amazonian and São Francisco cratons indicate parental magma origins that have experienced variable interaction with lithosphere after separating from a convecting mantle source. The Hf isotopic data indicate that zircon megacrysts from the Juína and Paranatinga kimberlite fields have signatures consistent with mildly depleted global kimberlites, pointing to either a more depleted (higher time-integrated Lu/Hf) mantle source, or that the parental melt interacted with mantle lithosphere with highly positive εHf characteristics. In contrast, APIP zircons display “enriched” low εHf_i characteristics, perhaps suggesting a source more influenced by interaction with metasomatized mantle lithosphere.