A precise age for the Utopia Granite, southwestern New Brunswick, Canada
Bibliographic record
Abstract
The Utopia Granite is part of the Saint George Plutonic Suite, a gabbroic to granitic assemblage of plutons of Late Silurian – Late Devonian age in southwestern New Brunswick. New U-Pb (ID-TIMS) analyses of five fractions of strongly air-abraded zircon grains define a discordant array which suggests that all five fractions have suffered at least some minor degree of post-crystallization Pb-loss and yielded an imprecise upper intercept age of 426.3 ± 5.9 Ma. Fifteen zircon grains analyzed by LA-ICP-MS yielded overlapping concordant analyses, from which a weighted average of the 206Pb/238U ages, excluding one younger age, is 428.3 ± 1.0 Ma (MSWD = 0.66, probability of fit = 0.81), which we interpret as the best estimate for the crystallization age of the Utopia Granite. This age suggests that the Utopia Granite may be the oldest component of the Saint George batholith, and 5–8 million years older than plutons of the contiguous coastal Maine magmatic province to the southwest.
 
 RÉSUMÉ
 
 Le granite Utopia fait partie de la suite plutonique de Saint-George, un assemblage gabbroïque à granitique de plutons du Silurien tardif et de la fin du Dévonien, dans le sud-ouest du Nouveau-Brunswick. De nouvelles analyses U-Pb (ID-TIMS) de cinq fractions de grains de zircon fortement altérés par l’air indiqueraient un assemblage discordant qui porte à croire que les cinq fractions ont subi au moins en partie une perte de plomb après la cristallisation. Les analyses ont permis d’établir de manière imprécise un âge géologique de 426,3 ± 5.9 Ma. Quinze grains de zircon analysés à l’aide des méthode LA-ICP-MS ont produit des résultats concordants qui se recoupaient, dont on a tiré une moyenne pondérée des âges 206Pb/238U de 428,3 ± 1,0 Ma, exception faite d’un âge plus jeune (déviation pondérée de la régression par moindres carrés = 0,66, probabilité de congruence = 0,81). Nous croyons qu’il s’agit là de la meilleure estimation qui soit de la période de cristallisation du granite Utopia. Ces analyses de datation suggèrent que le granite Utopia pourrait être la partie la plus ancienne du batholithe Saint-George, et de 5 à 8 millions d’années plus ancienne que les plutons de la province magmatique de la zone côtière contigüe du Maine, au sud-ouest.[Traduit par la redaction]
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How this classification was reachedexpand
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 | 0.000 |
| 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) | 0.006 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".