Abstract: Geochemistry and regional correlation of Middle Ordovician arc-related volcanic rocks from the Popelogan Inlier (Dunnage Zone), northern New Brunswick
Bibliographic record
Abstract
The Popelogan Inlier consists largely of mafic volcanic rocks of the Goulette Brook Formation, which underlies a thin unit of black chert (Popelogan Formation) containing early Caradocian (N. gracilis zone) graptolites. Four suites of mafic rocks are present, namely ( 1) picritic lapilli tutT, (2) basaltic to andesitic lapilli tuff, (3) low-Cr basalt, and (4) andesitic basalt. Suites (I) and (2) are volumetrically dominant. Suites ( 1) through (4) display incremental increases in absolute traceelement abundances, though all, except the andesitic basalt, are characterized by low HFSE contents. All samples display negative Nb and Ti and positive Th anomalies on traceelement spidergrams, typical of subduction-related basalt, and all plot within volcanic arc fields on tectonic discrimination diagrams. LREE abundances, sloping REE profiles (LaN/YbN = 2.7 to 7.6), and high Zr/Y (2.9-7.7) are typical of calcalkaline basalt and andesite. Trace-element systematics suggest derivation from a mantle source that was enriched in HFSE compared to normal MORB, prior to introduction of Th and LILE via metasomatizing fluids from the subducting slab. Primitive picritic tuff (high MgO, Cr; Mg# 62-81) must have been emplaced following rapid ascent, with minimal fractionation or crustal assimilation. Other chemical variations among the respective suites can be explained by different degrees of partial melting of a common mantle source, followed by variable amounts of fractionation. Volcanic rocks of the Goulette Brook Formation can be stratigraphically correlated with chemically similar arc-related basalts of Arenig-Llanvirn age in northern Maine and Newfoundland. In these areas, calc-alkaline arc volcanic rocks like those of the Goulette Brook Formation are transitional between older primitive arc tholeiite and younger back-arc basalt, and were probably generated during arc rifting. Arc volcanism occurred over an east-dipping subduction zone at the eastern margin of Japetus, and typically involved thinned, peri-Gondwanan continental crust. In New Brunswick, ensialic back-arc volcanism of the Miramichi terrane followed and accompanied rifting of the Popelogan arc. Chemical signatures in the Goulette Brook volcanic rocks similarly reflect the influence of continental crust and/or subcontinental lithosphere in enrichment of the mantle wedge.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".