U-Pb zircon evidence for an extensive early Archean craton in Zimbabwe: A reassessment of the timing of craton formation, stabilization, and growth

U-Pb single-zircon analyses provide direct evidence for an enlarged early A rchean craton forming the core to the present Zimbabwe craton. Virtually id entical dates from the south-central Tokwe segment (3455 +/- 2 Ma) and Midl ands (3456 +/- 6 Ma) parts of the craton strongly suggest their synchronous formation, during an event that formed a single early cratonic nucleus whi ch we propose to call the "Sebakwe protocraton." This is considered to unde rlie 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 da ted from Zimbabwe. A ca. 3350 Ma relatively undeformed and unmetamorphosed intrusive granitic phase constrains the timing of the high-grade metamorphi sm and the stabilization of the protocraton. Comparison with published Re-O s 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 majo r period of magma genesis and crustal formation within which the predominan t rocks of the exposed Zimbabwe craton were generated.