U-Pb zircon evidence for an extensive early Archean craton in Zimbabwe: a reassessment of the timing of craton formation

Horstwood, M.S.A., Nesbitt, R.W., Noble, S.R. and Wilson, J.F. (1999) U-Pb zircon evidence for an extensive early Archean craton in Zimbabwe: a reassessment of the timing of craton formation. Geology, 27 (8), 707-710. (doi:10.1130/0091-7613(1999)027<0707:UPZEFA>2.3.CO;2).

Abstract

U-Pb single-zircon analyses provide direct evidence for an enlarged early Archean craton forming the core to the present Zimbabwe craton. Virtually identical dates from the south-central Tokwe segment (3455 ± 2 Ma) and Midlands (3456 ± 6 Ma) parts of the craton strongly suggest their synchronous formation, during an event that formed a single early cratonic nucleus which we propose to call the “Sebakwe protocraton.” This is considered to underlie most of the current Zimbabwe craton. Parts of the craton are at least 3565 ± 21 Ma, a rock age reported here that represents the oldest rock dated from Zimbabwe. A ca. 3350 Ma relatively undeformed and unmetamorphosed intrusive granitic phase constrains the timing of the high-grade metamorphism and the stabilization of the protocraton. Comparison with published Re-Os data for the Zimbabwe craton strongly indicates a depleted subcontinental lithospheric mantle underlying the entire Sebakwe protocraton. Subsequent intrusive and volcanic activity from 3.0 to 2.6 Ga represents a second major period of magma genesis and crustal formation within which the predominant rocks of the exposed Zimbabwe craton were generated.

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