Similar V/Sc Systematics in MORB and Arc Basalts: Implications for the Oxygen Fugacities of their Mantle Source Regions
Bibliographic record
Abstract
V/Sc systematics in peridotites, mid-ocean ridge basalts and arc basalts are investigated to constrain the variation of fO 2 in the asthenospheric mantle.V/Sc ratios are used here to ' see through' those processes that can modify barometric fO 2 determinations in mantle rocks and/or magmas: early fractional crystallization, degassing, crustal assimilation and mantle metasomatism.Melting models are combined here with a literature database on peridotites, arc lavas and mid-ocean ridge basalts, along with new, more precise data on peridotites and selected arc lavas.V/Sc ratios in primitive arc lavas from the Cascades magmatic arc are correlated with fluidmobile elements (e.g.Ba and K), indicating that fluids may subtly influence fO 2 during melting.However, for the most part, the average V/Sc-inferred f O 2 s of arc basalts, MORB and peridotites are remarkably similar (À1Á25 to þ0Á5 log units from the FMQ buffer) and disagree with the observation that the barometric f O 2 s of arc lavas are several orders of magnitude higher.These observations suggest that the upper part of the Earth's mantle may be strongly buffered in terms of fO 2 .The higher barometric fO 2 s of arc lavas and some arc-related xenoliths may be due respectively to magmatic differentiation processes and to exposure to large, time-integrated fluid fluxes incurred during the long-term stability of the lithospheric mantle.
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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 | 0.003 | 0.002 |
| Science and technology studies | 0.000 | 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".