Geochemistry and petrogenesis of Ordovician arc-related mafic volcanic rocks in the Popelogan Inlier, northern New Brunswick
Bibliographic record
Abstract
The Popelogan Inlier consists mainly of mafic volcanic rocks (lapilli tuffs and massive to amygdaloidal, plagioclase-phyric flows) of the Middle Ordovician Goulette Brook Formation. Pyroclastic rocks include high-MgOCrNi picritic tuffs (type I) containing, in some cases, >20% MgO, and related high-MgO andesitic tuff (type II). High-MgO rocks were generated by 3040% partial melting of an enriched mantle source; type II is descended from type I mainly by fractionation of olivine. Mafic flows comprise basaltic andesites (type III) with low trace-element abundances and strongly fractionated, trace-element-enriched andesites (type IV). Types III and IV represent ~20 and ~10% partial melts, respectively, of a mantle source similar to that of the pyroclastic rocks, based on similar ratios of high field strength elements (HFSE). Unlike types I and II, petrogenesis of mafic flows involved fractionation of plagioclase and possibly amphibole. Volcanic arc signatures include negative Nb and Ti anomalies in all basalt types, along with low abundances of HFSE. Trace-element abundances are inconsistent with prior depletion in the back arc and require involvement of a mantle plume or subcontinental lithosphere. The highly magnesian composition of the picrites demands high melting temperatures and rapid transit through the crust, both of which suggest extension of the arc-bearing plate. Compositionally similar rocks in the South Pacific are associated with unusual tectono-magmatic settings involving ridge subduction, which may have established the necessary extensional environment. It is proposed that subduction of a plume-influenced ridge segment could explain the chemistry of the Goulette Brook volcanic rocks.
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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 | 0.003 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".