6533b852fe1ef96bd12ab523

RESEARCH PRODUCT

Age and isotopic evidence for the origin of the Archæan granitoid intrusives of the Johannesburg Dome, South Africa

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Abstract Results of RbSr, PbPb and SmNd whole rock, Rbr biotite and PbPb zircon evaporation analyses are presented for certain granitoid rocks from the Johannesburg Dome. These data indicate that the granodiorite, granite and leucosome from migmatite were emplaced ∼ 3090 Ma ago, were genetically related and were derived primarily from a source between ∼ 3300 and ∼ 3500 Ma old. A portion of the granodiorite and granite might have been derived from a source between ∼ 4000 and ∼ 4300 Ma old. The tonalite was emplaced ∼ 3170 Ma ago and was derived from a source between 3.3 and 3.5 Ga old. RbSr biotite-whole rock ages, ranging between about ∼ 2614 and ∼ 2080 Ma, probably reflect complete resetting during differential uplift, erosion and cooling of the granitoid rocks in the Neoarchaean and Palaeoproterozoic. If so, they apparently were not influenced by the emplacement of the ∼ 2060 Ma Bushveld Igneous Complex or the ∼ 2000 Ma Vredefort event. The granodiorite, granite and leucosome were emplaced coeval with and may be genetically related to compositionally similar plutonic and volcanic rocks in the Barberton area, Vredefort structure and Dominion Group.