Morphology and microstructure of chromite crystals from the Merensky Reef (Bushveld Complex, South Africa)
MetadataShow full item record
The Merensky Reef of the Bushveld Complex consists of two chromitite layers separated by coarse-grained melanorite. Microstructural analysis of the chromitite layers using electron backscatter diffraction analysis (EBSD), high-resolution X-ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals: fine-grained idiomorphic and large silicate inclusion-bearing crystals. The lower chromitite layer contains both populations, whereas the upper contains only fine idiomorphic grains. Most of the inclusion-bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre-existing smaller idiomorphic crystals. Two possible mechanisms have been proposed for sintering of chromite crystals: (1) amalgamation of a cluster of grains with the same original crystallographic orientation; and (2) sintering of randomly orientated crystals followed by annealing into a single grain. The EBSD data show no evidence for clusters of similarly oriented grains among the idiomorphic population, nor for earlier presence of idiomorphic subgrains spatially related to inclusions, and therefore are evidence against both of the proposed sintering mechanisms. Electron backscatter diffraction analysis maps show deformation-related misorientations and curved subgrain boundaries within the large, amoeboidal crystals, and absence of such features in the fine-grained population. Microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers, and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation.An alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals, formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during the magma influx that formed the Merensky Reef. The upper chromite layer formed from a subsequent magma influx, and hence lacked a mechanism to form dendritic chromite. This accounts for the difference between the two layers.
The final publication is available at link.springer.com
NOTICE: This is the author’s version of a work in which changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication.
Showing items related by title, author, creator and subject.
Morphology and microstructure of chromite crystals in chromitites from the Merensky Reef (Bushveld Complex, South Africa)Vukmanovic, Zoja; Barnes, S.; Reddy, Steven; Godel, B.; Fiorentini, M. (2013)The Merensky Reef of the Bushveld Complex consists of two chromitite layers separated by coarse-grained melanorite. Microstructural analysis of the chromitite layers using electron backscatter diffraction analysis (EBSD), ...
Zircon recycling and crystallization during formation of chromite- and Ni-arsenide ores in the subcontinental lithospheric mantle (Serranía de Ronda, Spain)González-Jiménez, J.; Marchesi, C.; Griffin, W.; Gervilla, F.; Belousova, E.; Garrido, C.; Romero, R.; Talavera, Cristina; Leisen, M.; O'Reilly, S.; Barra, F.; Martin, L. (2016)© 2017 Elsevier B.V.The ultramafic massifs of the Serranía de Ronda (namely Ronda, Ojén and Carratraca) are portions of Proterozoic (~1.2-1.8Ga) subcontinental lithospheric mantle (SCLM) affected by partial melting and ...
The structure of and origin of nodular chromite from the Troodos ophiolite, Cyprus, revealed using high-resolution X-ray computed tomography and electron backscatter diffractionPrichard, H.; Barnes, S.; Godel, B.; Reddy, Steven; Vukmanovic, Zoja; Halfpenny, Angela; Neary, C.; Fisher, P. (2015)Nodular chromite is a characteristic feature of ophiolitic podiform chromitite and there has been much debate about how it forms. Nodular chromite from the Troodos ophiolite in Cyprus is unusual in that it contains skeletal ...