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Formation of Bushveld anorthosite by reactive porous flow

Maier Wolfgang D., Barnes Sarah-Jane, Muir D., Savard Dany, Lahaye Yann et Smith W. D.. (2021). Formation of Bushveld anorthosite by reactive porous flow. Contributions to Mineralogy and Petrology, 176, (3), p. 1-12.

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URL officielle: http://dx.doi.org/doi:10.1007/s00410-020-01760-7

Résumé

Bushveld anorthosites commonly contain the so-called “mottles” comprising irregular, typically centimetric domains of oikocrystic pyroxene or olivine enclosing small, embayed plagioclase grains. The mottles were traditionally interpreted to result from solidification of trapped intercumulus liquid or via in situ crystallisation at the top of the crystal mush. Here, we present microtextural and compositional data of a mottle to place further constraints on the formation of anorthosite layers. Element maps generated by scanning electron microscopy reveal that plagioclase within and around the mottle has markedly elevated An contents (up to An95) relative to the host anorthosite and is strongly reversely zoned. Other unusual features, some of which were reported previously, include a halo of sub-vertically oriented, acicular phlogopite around the mottle, elevated contents of disseminated sulfides, and relatively evolved yet Ni-rich olivine (Fo71–75, 3000 ppm Ni). These features are interpreted to result from reactive porous flow of hot, acidic fluid enriched in nickel and sulfur through proto norite. The fluids dissolved mafic minerals and leached alkalis from the outer rims of plagioclase grains. Reconnaissance studies suggest that reversed zoning of plagioclase is a common feature in Bushveld norite and anorthosite. This implies that reactive porous flow could have been far more pervasive than currently realised and that Bushveld anorthosite layers formed through recrystallisation of norites.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:176
Numéro:3
Pages:p. 1-12
Version évaluée par les pairs:Oui
Date:2021
Sujets:Sciences naturelles et génie > Génie
Sciences naturelles et génie > Sciences appliquées
Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:Bushveld complex, layered intrusions, anorthosite, reactive porous flow, Complexe Bushveld, intrusions stratifiées, anorthosite, écoulement poreux réactif
Déposé le:18 févr. 2021 21:21
Dernière modification:18 févr. 2021 21:21
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Creative Commons LicenseSauf indication contraire, les documents archivés dans Constellation sont rendus disponibles selon les termes de la licence Creative Commons "Paternité, pas d'utilisation commerciale, pas de modification" 2.5 Canada.

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