Lu-Hf analyses of zircon from the Makoppa Dome and Amalia-Kraaipan area: 1 implications for evolution of the Kimberley and Pietersburg blocks of the Kaapvaal Craton.
Résumé
Previously dated zircon crystals from the Amalia-Kraaipan granite-greenstone beltsand Makoppa Dome were analysed for their Lu-Hf isotopic characteristics to refine the geological evolution of these areas. Samples from the Makoppa Dome, belongingto the Pietersburg Block, largely fall within the epsilon Hf-age range for granitoids from the eastern part of the block. However, the oldest 3.01-3.03 Ga trondhjemitic gneisses show that reworking of juvenile mafic crust started earlier in the western than the eastern part of the block, suggesting a diachronous tectonic evolution. Thethree granitoids from the Amalia-Kraaipan area fall within the field for Pietersburg andKimberley block granitoids. Contribution from older crustal material is seen in a 3.08Ga schist, likely derived from a volcanic protolith, from the Madibe Belt, in the far eastof the Kimberley Block, with a mantle extraction age of 3.25-3.45 Ga. The datasuggest that the Kimberley Block, like the Pietersburg Block, also contains (minor)ancient crustal components, derived from a depleted mantle source prior to 3.1 Ga.The new data suggest that the Kimberley and Pietersburg blocks underwent a verysimilar Paleo- to Mesoarchean crustal evolution, with a major crust formation event at 3.1-3.0 Ga followed by successive crust reworking until 2.77 Ga. Lavas of theVentersdorp Supergroup, for which zircons from a ca. 2.75 lapilli tuff give Hfi of +2,are the first evidence of a juvenile source, after 300 Myr of crustal reworking.
Domaines
Géochimie
Origine : Fichiers produits par l'(les) auteur(s)
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