Emplacement and Differentiation of the Black Sturgeon Sill, Nipigon, Ontario: A Principal Component Analysis
Notice bibliographique
Résumé
Magmatic emplacement and differentiation processes typically produce compositional or petrographic signatures that are easily recognized and interpreted. However, these signatures can sometimes be indistinct or ambiguous, particularly when the available data sets are limited. Detailed sampling of a continuous drill core through the 250 m thick Black Sturgeon Sill (Nipigon, Ontario) provides an ideal opportunity to rigorously characterize the compositional variance in a natural system using principal component analysis. We identify three significant principal components, or composite variables, that together account for $90% of the total major-oxide variation in our data set and evaluate the petrogenetic significance of each. The first principal component is controlled by the contrast between residually-enriched liquids (which we interpret as evolved interstitial melt; PC1 > 0) and olivine anorthitic plagioclase (which we interpret as entrained crystal cargo; PC1 < 0). The second principal component is controlled by the contrast between 'gabbroic' (rich in plagioclase and augite; PC2 > 0) and 'ferrous' (iron-rich; PC2 < 0) compositions. The third principal component is controlled by the contrast between compositions dominated by felsic (PC3 > 0) and mafic (PC3 < 0) minerals. Compositional groupings, identified using k-means cluster analysis, correspond closely to observed petrographic zonation in the sill and demonstrate that the sill is a composite intrusion constructed from at least three sequential phases of magma injections. The first phase, with PC1$PC2$PC3$0, is a typical olivine diabase. The second phase, with elevated PC2, is dominated by plagioclase and augite, with little or no olivine. The final phase, with PC1 < 0, is the most primitive and was intruded as a slurry of plagioclase and olivine crystals. After substantial (but not complete) crystallization, interstitial melt was redistributed, particularly within the uppermost 40 m of the sill. This produced a heterogeneous upper zone, with PC1 > 0, in which highly evolved liquids collected in decimetre-scale lenses and patches. This study illustrates the value of principal component analysis for interpreting complex petrologic systems. Previous studies have demonstrated the value of principal component analysis for simplifying the representation of complex, multidimensional data sets. In this study, however, the primary benefit is the ease with which the petrogenetic processes responsible for compositional evolution in a particular system can be identified. By using the principal components as indices for the various processes and mapping their stratigraphic variations through the Black Sturgeon Sill, this study illustrates a broader application of principal component analysis that could be applied to many other systems of petrologic interest.
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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) | 0,006 | 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 ».