Erratic behavior of platinum-group elements along an olivine–Cr-spinel cotectic in sulfide-undersaturated basaltic magma: roles of Cr-spinel and alloys
Bibliographic record
Abstract
The behavior of platinum-group elements (PGE) in sulfide-undersaturated primitive magmas may be controlled by crystallization of either Cr-spinel, platinum-group minerals (PGM) or olivine. Evaluation of the PGM-hosted PGE portion is challenging because PGM in volcanic rocks are small and rare. We report on the sizes and compositions of PGM associated with Cr-spinel, the PGE content of Cr-spinel and olivine, and the bulk rock PGE content from sulfide undersaturated arc volcanics of the Tumrok range (Eastern Kamchatka). Platinum-iron and Ir-Os alloys (< 30 to > 3000 nm in size) form inclusions in Cr-spinel. Their presence and composition are mostly independent of Cr-spinel chemistry. Bulk rock PGE contents are erratic and PGE concentrations in Cr-spinel are exceptionally variable (up to 2 orders of magnitude). Whereas PGM inclusions in Cr-spinel and PGE in solid solution in Cr-spinel significantly contribute to the bulk rock PGE budget, a considerable portion of the PGE must be present associated with minerals other than Cr-spinel. The variable PGE content of the rocks is attributed to a combination of: (a) disequilibrium kinetic effects at the Cr-spinel-melt boundary layer, strongly affecting PGE partitioning into Cr-spinel and crystallization of PGM in the layer; (b) the presence of some sufficiently large PGM to cause nugget effects; and (c) melt degassing.
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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 | 0.000 |
| 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) | 0.001 | 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".