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A comparison of trace element concentrations in chromite from komatiites, picrites, and layered intrusions: implications for the formation of massive chromite layers

Barnes, Sarah-Jane, Mansur, Eduardo T., Maier, Wolfgang D. ORCID: https://orcid.org/0000-0002-8654-6658 and Prevec, Stephen A. 2022. A comparison of trace element concentrations in chromite from komatiites, picrites, and layered intrusions: implications for the formation of massive chromite layers. Canadian Journal of Earth Sciences 60 (2) 10.1139/cjes-2022-0064

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Abstract

By examining the minor and trace element contents of chromites from three intrusions—the Bushveld Complex (South Africa), the Stillwater Complex (USA), and the Great Dyke (Zimbabwe)—and comparing these chromite compositions with those of magmas from which they could have formed (komatiites and picrites) we conclude that (i) the variations in Ti, V, Sc, and Ga contents across stratigraphy and across individual layers do not support the model of magma mixing leading to chromite-only crystallization, (ii) the chromites from the lowest levels of the intrusions could have crystallized from komatiite liquids that were contaminated with continental crust, (iii) the Great Dyke chromites have the highest Cr# and lowest incompatible element contents and formed from a liquid closest to komatiite, (iv) all of the chromites, except those of the Dunite Succession of the Great Dyke have equilibrated with a liquid that also had crystallized pyroxene, (v) the Great Dyke and Stillwater chromites show a narrower range in composition than the Bushveld chromites, and (vi) Chromites from the western limb of the Bushveld Complex contain much higher V contents than all the other chromites. This requires either, that the oxygen fugacity (fO2) was lower in the western Bushveld or that the chromites equilibrated with a V-rich magma. We favor a model where chromite and silicate minerals crystallized in cotectic proportions (∼2:98). The chromite, silicates, and transporting liquid are emplaced into the magma chamber. During emplacement the chromite and silicate separated due to viscous particle flow to form a massive chromite layer overlain by silicates.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Earth and Environmental Sciences
Publisher: Canadian Science Publishing
ISSN: 0008-4077
Date of First Compliant Deposit: 2 February 2023
Date of Acceptance: 24 October 2022
Last Modified: 07 May 2023 02:39
URI: https://orca.cardiff.ac.uk/id/eprint/156472

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