Petrogenesis and metamorphism of mafic rocks, Atlantis Massif, IODP Expedition 357: implications of two episodes of magmatism
Bibliographic record
Abstract
The petrogenesis and metamorphism of International Ocean Discovery Program (IODP) Expedition 357 (Atlantis Massif, Mid-Atlantic Ridge) mafic rocks is the focus of this paper. At least two phases of magmatism are identified. Later Phase I metamorphosed mafic intrusive rocks (MMIs) are moderately to extremely chloritized, recording loss on ignition (LOI) of 3.33–9.99 wt%, and latest Phase II basalts are exceptionally fresh, with LOI of 0.09–1.03 wt%. Phase I MMIs have Fe-chromite identical to Atlantis Massif serpentinites that have undergone melt-impregnation and Phase II basalt Cr-spinels are analogous to those of Atlantis Massif peridotites that have not undergone secondary melt-impregnation. Whole-rock Cr/Y relations of the Phase II basalt record melt fractions ( F ) of c . 16–25% and melt–liquid equilibria established for Phase II basalt olivine yield crystallization temperatures of 1173–1219°C similar to mid-ocean ridge basalt ( c . 1125–1290°C). Trivariant plots of Na 2 O–CaO–MgO and XRD analysis confirm extreme chloritization of the Phase I MMIs. Phase I MMI spinel is predominantly Fe-chromite that formed under amphibolite-facies conditions ( c . 500°C). Subsequent to peridotite exhumation, serpentinization and Phase I magmatism, an episode (or episodes) of asthenospheric upwelling resulted in contact metamorphism caused by Phase II magmatism.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".