Geochemistry and field relations of greenstones in the Moretown and Cram Hill formations, Montpelier Quadrangle, Vermont
Bibliographic record
Abstract
Greenstones and other metaigneous rocks are abundant within parts of the metasedimentary Moretown and Cram Hill Formations' Ordovician-age rocks that are part of a north-south trending Taconian thrust slice running the length of Vermont and into adjacent parts of New England and Quebec. This research focuses on greenstone samples taken throughout the Montpelier Quadrangle in central Vermont, and in particular on two strip maps through Cram Hill and Moretown rocks just east of the Richardson Memorial Contact (RMC), a boundary separating pre-Silurian from Silurian rocks. Greenstones occur within the steeply dipping metasedimentary lithologies as discontinuous, usually concordant bodies 10 cm to 7 m thick. Epidote-chlorite-albite-quartz-calcite-actinolite mineralogy is consistent with greenschist facies metamorphism, and some remnant igneous textures remain. Geochemistry indicates the greenstones were tholeiitic basalts. Major and trace element plots suggest that the greenstones are related by fractional crystallization, particularly of olivine. On tectonic discrimination diagrams, these greenstones plot broadly as mid-ocean ridge basalt (MORB). Two geochemical groups are clearly distinguished by Rare Earth Element (REE) data and discernible in other trace element plots. The depleted REE group shows MORB or backarc basin basalt (BABB) affinities and is associated with the Cram Hill Formation. Greenstone samples from the Moretown Formation have slightly enriched LREE patterns and other trace element characteristics consistent with BABB. Differences in these geochemical groups indicate that they must have formed in different environments, either spatially or temporally. Findings from both groups are strongly similar to some rocks in Vermont and Massachusetts that have been interpreted as BABB (Kim and Jacobi, 1996; Kim et al. 2003), and to known BABB from the Sea of Japan (Allan and Gorton, 1992). This reinforces the interpretation of the Montpelier greenstones as backarc basin basalt.
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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 | 0.001 |
| 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".