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Journal of Petrology Volume 43 Number 2 Pages 271-290 2002
© Oxford University Press 2002
High fO2 Metasomatism During Whiteschist Metamorphism, Zambezi Belt, Northern Zimbabwe
CRUSTAL GEODYNAMICS GROUP, SCHOOL OF GEOGRAPHY AND GEOSCIENCES, UNIVERSITY OF ST. ANDREWS, ST. ANDREWS KY16 9AL, UK
The Kadunguri Whiteschists are a group of talc- and kyanite-bearing lithologies that occur in the Chewore Inliers from the Zambezi Belt of northern Zimbabwe. They crop out on the southern margin of the Chewore Ophiolite Terrane, a Mesoproterozoic ophiolite and island arc, as a 5 km x 1·5 km, southeasterly dipping, semi-continuous block, and contain the second known natural occurrence of yoderite. Major element analyses define the whiteschists within the relatively simple MFASH system. Major and trace element analyses indicate that the whiteschists originate from the metasomatic alteration of alkalic ocean-island-type metabasalts similar to those in the underlying Ophiolite Terrane. Synmetamorphic or metasomatic mineral parageneses indicate peak PT conditions of between 13 and 15 kbar at 550600°C, and the highly oxidizing nature of all reactions indicates the presence of a high fO2 metasomatic fluid. The peak PT conditions require that this synmetamorphic, exotic metasomatic fluid was available at depths near 55 km. The age of high-pressure metamorphism is constrained within the Pan African tectonothermal cycle at 550520 Ma. Tectonometamorphism in the Zambezi Belt is related to a period of extensive crustal thickening possibly related to amalgamation of Gondwanaland.
KEY WORDS: Congo Craton; high pressure; Kalahari Craton; metasomatism; whiteschist; Zambezi Belt
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