Abstract

The Tugela Rand layered intrusion is a metamorphosed, stratiform body located within the Nappe Zone of the mid-Proterozoic Natal mobile belt, South Africa. The intrusion comprises three macrorhythmic units (zones I, II, III), each consisting of the sequence dunite-websterite-gabbronorite. Possible overturning is evidenced by a downward decrease in the proportion of ultramafic to mafic rocks from zone I to zone III, a downward trend of iron enrichment from En87 to En76, and inverted erosion scours within the cumulates. The intrusion has undergone both granulite- and amphibolite-facies metamorphism. The former is attributed to recrystallization in the presence of residual magmatic heat and the latter to regional metamorphism after or during further cooling of the intrusion. Overturning of the intrusion may have occurred during late-stage horizontal tectonics, when the Nappe Zone was transported northward over the southern boundary of the Kaapvaal craton. Overturned sequences have not previously been identified within the Nappe Zone.

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