Implications of metallic iron for diamonds and nitrogen in the sublithospheric mantle
Bibliographic record
Abstract
Recently published experimental data suggest that the Earth’s mantle below ∼250 km is saturated in metallic Fe, reaching a concentration of ∼1 wt.% Fe0 throughout the lower mantle and buffering oxygen fugacity by Fe0↔Fe2+ reactions. Metallic Fe in the mantle bears important implications for N, which behaves as a moderately siderophile element. Here, we propose that the trapping of N in (Fe, Ni) metal and Fe-carbides during diamond growth may account for the characteristically low N content of diamonds from the sublithospheric mantle. This model may also explain the origin of especially valuable, large, anhedral, flawless Type II (N-free) diamonds, like the Cullinan, that comprise a minor part of world diamond production. Partition coefficients of N (DN) between diamond and metallic Fe within DN = 0.0005–0.013 have been demonstrated in high-pressure experiments for diamond synthesis and in a natural sample of a N-poor lower mantle diamond with inclusions of Fe-nitrocarbide. More N is incorporated into diamond if it grows in the lithosphere, where there is no ambient Fe0 to trap N. As a broader implication, the recognition of Fe0 in the mantle and its affinity for N suggests metallic Fe should be a major host of mantle N. Retention of primordial mantle N in metallic Fe could explain the high N/36Ar and low 15N/14N ratios of the mantle compared with the atmosphere.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".