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<p>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<sub>i</sub> 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 δ<sup>18</sup>O 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<sub>i</sub> characteristics, perhaps suggesting a source more influenced by interaction with metasomatized mantle lithosphere.</p>

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

  • 期刊论文

  • 发表日期：

    2025年5月9日

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  • Izaac Cabral-Neto,
  • D. Graham Pearson,
  • Excelso Ruberti,
  • Yan Luo,
  • Richard A. Stern,
  • Rogério G. Azzone,
  • Matthew F. Hardman,
  • Vidyã V. Almeida,
  • Francisco V. Silveira

摘要

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 εHfi 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 εHfi characteristics, perhaps suggesting a source more influenced by interaction with metasomatized mantle lithosphere.