A comparison of Eastern North America and Coastal New England magma suites: implications for subcontinental mantle evolution and the broad-terrane hypothesis
Bibliographic record
Abstract
New England and Maritime Canada host two major suites of Mesozoic diabase dykes. The oldest is the Coastal New England dykes that were emplaced between 225 and 230 Ma. These rocks are dominantly alkaline with trace element and isotopic compositions indicative of a high-238U/204Pb mantle (HIMU) source. The oldest of the ~200 Ma Mesozoic rift magmas is represented by the Talcott basalt of the Hartford basin and its feeder dykes. External to the basin is the compositionally equivalent Higganum dyke. The extension of the Higganum, the Onway dyke in New Hampshire, is identical in major and trace element and isotopic compositions indicating that the dyke system represented a feeder to flows of flood basalt proportions. The Talcott system rocks have some trace element similarities with arc basalts and have been interpreted as representing melts of a subduction zone modified mantle beneath the Laurentian- Gondwanan suture. Incompatible trace element ratios and Ba, Th, and U values are, however, unlike arc basalts and are more indicative of crustal contamination of the primary magma. The coastal New England magmas have oceanic island basalt signatures that are generally thought to represent plume-tail magmatism, which is antithetic to a plume-head origin for the younger eastern North America magmas. However, coastal New England rocks have the same trace element signatures as the alkaline rocks of the Loihi seamount, which represent the pre-shield stage to the voluminous tholeiitic magmatism in Hawaii.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".