U-Pb dating of the Musquodoboit Batholith, southern Nova Scotia: evidence for a protracted magmatic-hydrothermal eventin a Devonian intrusion
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Bibliographic record
Abstract
The first high-temperature geochronometric data are presented for the peraluminous, multiple phase Musquodoboit Batholith, the second largest intrusion in the Meguma terrane of Nova Scotia. Previous geochronology includes 40Ar/39Ar mica (i.e., muscovite and biotite, 363 to 370 Ma) and Rb-Sr whole-rock (266 Ma) and mineral (biotite, 370 Ma) ages. These earlier ages contrast with new data for zircon and monazite which together define an age of 378 ± 1 Ma for the high-temperature crystallization (i.e., ca. >650– 800°C) and, therefore, provide a more reliable time for emplacement and solidification of the batholith. Integration of the new data with previous work is reconciled in the context of a protracted cooling history for the intrusion that reflects the depth of emplacement (i.e., 10–12 km) and potentially high geothermal gradient due to the radioelement-rich nature of parts of the complex. This study suggests that absolute dating of large intrusive bodies emplaced at moderate crustal levels (i.e., ≥3– 4 kbars) should employ high-temperature geochronometers rather than the commonly used 40Ar/39Ar mica technique, which is limited due to the relatively lower blocking temperatures of ≤350°C. RÉSUMÉ Les premières données géochronométriques à haute température visent le batholite hyperalumineux à phases multiples de Musquodoboit, deuxième intrusion en importance dans le terrane de Meguma, en Nouvelle-Écosse. Les données géochronologiques antérieures comprennent des datations 40Ar/39Ar de mica (c.-à-d. muscovite et biotite, de 363 à 370 Ma), une datation Rb-Sr de roche totale (266 Ma) et une datation minérale (biotite, 370 Ma). Ces âges plus précoces contrastent avec les nouvelles données du zircon et de la monazite, qui confèrent ensemble un âge de 378 ± 1 Ma par cristallisation à haute température (c.-à-d. à environ > 650 à 800 °C) et qui fournissent par conséquent une datation plus fiable de la mise en place et de la solidification du batholite. L'intégration des nouvelles données concordent avec les travaux antérieurs compte tenu du refroidissement passé prolongé de l'intrusion correspondant à la profondeur de l'enfouissement (c.-à-d. 10 à 12 kilomètres) et du gradient géothermique potentiellement élevé en raison de la nature riche en radioéléments de certaines parties du complexe. Cette étude permet de supposer qu'il faut employer des géochronomètres à température élevée plutôt que la technique couramment utilisée de la datation 40Ar/39Ar au mica, qui est limitée par des températures de fermeture relativement plus faibles de ≥ 350 °C, pour réaliser une datation absolue des masses intrusives importantes enfouies à des niveaux crustaux moyens (c.-à-d. ≥ 3– 4 kilobars). [Traduit par la redaction.]
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it