Role of Chamber Replenishment in the Formation of the Merensky Reef and its Footwall Anorthosite
Notice bibliographique
Résumé
Abstract The Merensky Reef of the Bushveld Complex represents a magmatic unconformity that some researchers attribute to chamber replenishment by relatively primitive magma. It is propounded that cumulate rocks in this chamber reacted with replenishing melt, as part of the process that ultimately produced chromitite stringers and reef-style platinum-group element mineralization. This study investigates as to whether chamber replenishment contributed to the formation of the Merensky Reef and its underlying anorthosite at the Rustenburg Platinum Mine in the western lobe of the Bushveld Complex. At this location, the Merensky Reef is a coarse-grained pyroxenite bracketed by millimeter-scale chromitite stringers. This sequence is underlain by a centimeter-scale anorthosite which in turn is underlain by leuconorite. The leuconorite comprises normally zoned cumulus orthopyroxene with poikilitic rims (Mg80-79) and cumulus plagioclase (An80-58), where the latter defines a magmatic fabric indicative of gravitational settling of tabular crystals in a quiescent melt. The contact between leuconorite and anorthosite is marked by an increased abundance of late-stage accessory minerals, and the composition of poikilitic orthopyroxene at this horizon is consistent with trapped liquid shift. Plagioclase crystals in the anorthosite are variably zoned (An79-64) and record a magmatic fabric that strengthens with proximity to the reef. This unit is traversed by sinuous networks of sulfides, pyroxenes, quartz, and very fine-grained chromite that terminate at the contact with the leuconorite. The lower chromitite hosts both amoeboidal and blocky chromite crystals that are enclosed by complexly zoned plagioclase oikocrysts in the lower two-thirds and by orthopyroxene oikocrysts in the upper third. The upper chromitite hosts only blocky crystals, similar to those in the upper portion of the lower chromitite. Microtextural characteristics of the amoeboidal crystals coupled with their propensity to host polymineralic inclusions, suggests that these were initially skeletal crystals that subsequently underwent dissolution-reprecipitation. There is no discernible chemical difference between amoeboidal and blocky crystals; however, accessory mineralogy and chromite chemistry imply that the upper portion of the lower chromitite and the upper chromitite experienced post-cumulus re-equilibration with evolved intercumulus silicate melt. Our observations are consistent with the anorthosite being a restite of partially molten leuconoritic cumulates. This theory is supported by thermodynamic modelling that demonstrates that under certain conditions, replenishing melts can reconstitute noritic cumulates to anorthosite, troctolite, or feldspathic orthopyroxenite restites. The porosity generated during this process was exploited by downward percolating sulfide melt that displaced a proportionate amount of intercumulus silicate melt upward to the level of the nascent reef. Initially, these partial melts were likely relatively volatile-rich, triggering Cr-supersaturation at the cumulate-melt interface, and later became Cr-bearing with the consumption of poikilitic orthopyroxene and very fine-grained chromite.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».