Magmatic evolution of the Late Devonian Mount Douglas leucogranites, southwestern New Brunswick, Canada; an example of extreme fractional crystallization
Bibliographic record
Abstract
The Late Devonian Mount Douglas intrusive suite (MD, ~600 km2) of southwestern New Brunswick, Canada, eastern part of the Saint George Batholith, is a suite of peraluminous leucogranites extended from Red Rock Lake to Mount Douglas. Extreme fractional crystallization associated with formation of this suite is the most important factor affecting the magmatic evolution, producing three compositionally and chronologically different intrusive units, Dmd1, Dmd2, and Dmd3. Petrochemical data show that the subunits of the Mount Douglas Granite have within-plate geochemical character with evidence of hybrid I- and S-type affinity. Very low K/Rb (average 102.7), Nb/Ta (? 6.8), and Zr/Hf (? 37.45) ratios in Dmd3 compared to Dmd1 possibly reflect significant involvement of extreme low T crystal fractionation in the last- stages of magmatic differentiation; The continuous variation trends for many major and trace elements (e.g., Zr vs. TiO2, Zr/Hf vs. K/Rb, F vs. K/Rb, and Pb vs. Ba) suggest that probably Dmd2 and Dmd3 were generated by extensive fractionation of the parental Dmd1 magma. Also, normalized to the least-evolved sample of the MG granites (Dmd1), the Dmd3 unit is the most enriched in Rb, Th, U, Ce, Ta, Pb, Nd, Sm, Dy, Y, Yb, and Lu, and depletion of Cs, Ba, Sr, P, Zr, Eu, and Ti content, reflects their production of the same parental magma by crystal fractionation from Dmd1 to Dmd3. A flat "birdwing shape" REE patterns with the most pronounced negative Eu anomalies and the lowest (La/Yb)N (ranging from 1.7-7.4) ratios of Dmd3 show the highly evolved attributes of Dmd3. Calculation of zircon saturation temperatures supports an interpretation of crystal fractionation from Dmd1 to Dmd3. Estimated average temperatures using the bulk rock Zr composition for Dmd1, Dmd2, and Dmd3 range 747-826°C, 733-817°C, and 729-816°C, respectively. All above data suggest that they might have a single genetic group with different fractionation originated from a homogenous parental magma, in which this fractionation increases from the early unit (Dmd1) to the latest unit (Dmd3); significant mineral occurrences, such as Sn, W, and Mo, seem to be mostly associated with the latest and most highly differentiated Dmd3 intrusive phases.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".