High-pressure (HP), granulite-facies thrusting in a thick-skinned thrust system in the eastern Grenville Province, central Labrador
Notice bibliographique
Résumé
In the eastern Grenville Province of central Labrador, the Grenvillian Grand Lake thrust system (GLTS) comprises part of a thick-skinned thrust system separating the allochthonous and parautochthonous Grenvillian terranes. North-northwest directed thrusting on the GLTS during the Grenvillian orogeny carried the Labradorian (1710-1600 Ma) rocks of the Cape Caribou River Allochthon (CCRA) and the overlying Mealy Mountains terrane (MMT), onto a footwall composed of similar aged granitoid gneisses of the Groswater Bay and Lake Melville Terranes (GBT and LMT). The CCRA is principally composed of an AMCG suite, with the GLTS comprising a basal shear zone about 1km thick characterized by mylonite and straight gneisses developed under granulite- and upper amphibolite-facies conditions. Lithologies in the GLTS include highly strained dioritic to granitic orthogneiss (straight gneiss) comprising alternating mafic and felsic layers consisting of a mineralogy composed of garnet, clinopyroxene, amphibole, plagioclase, quartz and minor orthopyroxene which locally defines the stretching lineation. The footwall rocks of the GBT and LMT were metamorphosed under upper amphibolite facies conditions during Labradorian orogenesis. -- Field studies and published U-Pb data indicate that the extent of mylonitization and recrystallization induced by thrusting along the GLTS diminish rapidly upward into the allochthon and downward into the footwall rocks. U-Pb metamorphic ages within the CCRA and footwall rocks are Labradorian (1710-1600 Ma), whereas U-Pb metamorphic ages from the recrystallized rocks of the GLTS define two Grenvillian populations at 1040 and ~1010 Ma, which are correlated with the Ottawan and Rigolet orogenies respectively. -- Detailed analysis of appropriate, low variance mineral assemblages within the GLTS and adjacent footwall and hangingwall rocks was carried out to determine the P-T conditions of thrusting during the Grenvillian orogenesis using the TWEEQU software. Resultant P-T estimates associated with Grenvillian thrusting in the GLTS yield a consistent grouping of ~875 ± 50°C and 14 kbar using garnet-clinopyroxene and garnet-amphibole thermobarometry on the porphyroblastic assemblage, and 700 ± 50°C and 6-9 kbar using garnet-amphibole thermobarometry on the matrix assemblage, consistent with textural and mineralogical evidence of decompression. On the basis of core-rim P-T vectors in single grains it is concluded that non-synchronous closure of the geobarometric and geothermometric reactions occurred in some samples, and thus the highest P-T estimates are 'apparent peak' estimates that underestimate the true peak conditions. Although unquantified, the degree of underestimation of peak conditions is considered to be small on the basis of independent petrological considerations. -- Detailed petrography has revealed a wide range of fabrics elements that are related to thrusting, but a precise link between the P-T estimates and the available U-Pb database is not currently possible. A tentative tectonic model for this part of the Grenville orogen involves formation of a crustal-scale orogenic wedge by thrust imbrication during the Ottawan orogeny (~1040 Ma), with development of high-pressure (HP) granulites (~875 °C and ~14 kbar) at the base of the wedge. The HP granulites were uplifted up a crustal-scale ramp and exhumed during both Ottawan (~1040 Ma) and Rigolet times (~1010-1000 Ma). Recrystallization in the GLTS during the Rigolet orogeny took place below the closure temperature for the Fe-Mg exchange geothermometers employed and must have been principally driven by ingress of H₂O and dynamic recrystallization. It is inferred that rapid uplift, exhumation and cooling of the orogenic wedge were facilitated by normal faulting at the top of the wedge, which brought the Mealy Mountains terrane, virtually unmetamorphosed during the Grenvillian orogenesis, into tectonic contact with the CCRA with the HP granulite-facies GLTS shear zone at its base. -- This study points out the importance of integration of metamorphic petrology with geochronology in tectonic studies and emphasizes the significance of deformation as a mechanism to induce recrystallization and resetting of geothermobarometers and U-Pb systematics in dry metamorphic rocks.
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 | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,001 | 0,003 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,003 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 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 ».