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Minerals 2018, 8(4), 144; https://doi.org/10.3390/min8040144

The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth?

1
School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa
2
Department of Geology & Geophysics, Louisiana State University, E235 Howe Russell Kniffen, Baton Rouge, LA 70803, USA
*
Author to whom correspondence should be addressed.
Received: 21 February 2018 / Revised: 26 March 2018 / Accepted: 28 March 2018 / Published: 3 April 2018
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Abstract

The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as “cyclic unit”, typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with detailed petrographic and textural analyses of the Merensky Unit to determine whether it is a “cyclic unit” sensu stricto. The study indicates that the bulk of the platinum-bearing chromitite-feldspathic orthopyroxenite developed through heterogeneous nucleation and in situ growth during multiple replenishment events. The overlying leuconorite developed above a gradational boundary, reflecting mixing following replenishment by a relatively more evolved magma. The bulk of this unit also formed in situ. The uppermost poikilitic anorthosite formed above a distinct boundary through a subsequent injection of a plagioclase-saturated magma, which crystallised in situ. Processes of gravitational settling and local remobilisation of crystals cannot be discounted from contributing to the development of the unit. The final textures throughout the unit developed through pervasive textural equilibration, with extensive fluid-mediated textural equilibration forming the megacrystic feldspathic orthopyroxenite. The evidence for at least five replenishment events indicates that the Merensky Unit is not a cyclic unit; therefore, the genetic term, “Merensky Cyclic Unit”, is misleading and its use should be carefully considered in future work. View Full-Text
Keywords: Bushveld Igneous Complex; Merensky Reef; crystal size distribution; in situ crystallization; gravitational settling; cyclic layering Bushveld Igneous Complex; Merensky Reef; crystal size distribution; in situ crystallization; gravitational settling; cyclic layering
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Hunt, E.J.; Latypov, R.; Horváth, P. The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth? Minerals 2018, 8, 144.

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