Formation of Igneous Layering in Granodiorite by Gravity Flow: a Field, Microstructure and Geochemical Study of the Tuolumne Intrusive Suite at Sawmill Canyon, California
Notice bibliographique
Résumé
Layered granites and granodiorites occur in many plutons. They occur, together with non-layered granodiorites, at the margin of the Tuolumne Intrusive Suite, one of the largest late Cretaceous intrusions in the Sierra Nevada. Results from field observations, quantitative microstructural analysis and whole-rock compositions from the non-layered Kuna Crest, Half Dome and Cathedral Peak granodiorites and layered granodiorites from the Sawmill Canyon area are compared to determine which processes contributed to the formation of the layering. The non-layered granodiorites have foliated but homogeneous microstructures, which are attributed to the orientation of crystals with high aspect ratios when the magma flowed before solidification; their compositions are consistent with magma mixing and fractional crystallization. The microstructure in the layered granodiorite is heterogeneous, and shows normal gradation of the dense, primocryst minerals magnetite, hornblende and titanite at the base, and inverse size gradation with large crystals of the less dense primocryst phases plagioclase and biotite at the top, and a systematic change in the preferred orientation of minerals from base to top. Macroscopic structures in the layers indicate erosion and the action of traction currents when the layers formed, and the sinking of the dense minerals and rise of interstitial melt immediately afterwards. The layered rocks have similar grain size and mineral compositions to the non-layered granodiorites, and thus could be derived from the same magmas as the Kuna Crest, Half Dome and Cathedral Peak non-layered granodiorites. The major and trace element variations in the layered rocks are very different from those in the non-layered rocks and indicate a strong segregation of crystals during formation of the layers. However, the separation process did not fractionate the main rare earth element-bearing phases from one another. The macrostructure and microstructural features in the layers resemble those from hyper-concentrated sediment gravity flows. The layering is interpreted to have formed from gravity flows of melt and crystals initiated by syn-magmatic tectonic deformation and seismic shaking. Two types of layering are identified; one, called normal layering, represents material derived from a single granodiorite magma and deposited from a relatively low-energy gravity flow, whereas the other, called melanocratic layering, incorporated mafic minerals eroded from the substrate, had the felsic tops of layers eroded off by subsequent flows, incorporated crystals from more than one magma source and formed from gravity flows that had higher energy.
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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) | 0,000 | 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 ».