Coexisting pseudobrookite, ilmenite, and titanomagnetite in hornblende andesite of the Coleman Pinnacle flow, Mount Baker, Washington: Evidence for a highly oxidized arc magma
Bibliographic record
Abstract
Pseudobrookite microphenocrysts occur in cognate inclusions in the ~305 ka Coleman Pinnacle hornblende andesite flow from the Mount Baker volcanic field, Washington. Pseudobrookites are associated with hornblende phenocrysts and glomerophyric clusters of orthopyroxene, clinopyroxene, plagioclase, ilmenite, titanomagnetite, apatite, and zircon in a matrix of fresh rhyolitic glass. Grains of pseudobrookite are rimmed by or intergrown with ilmenite. These textures are analogous to those observed between armalcolite and ilmenite in high-Ti lunar basalts. In a unique occurrence, pseudobrookite, and titanomagnetite form a symplectitic intergrowth surrounding a core of ilmenite. Mass balance calculations show that the pseudobrookite + titanomagnetite assemblage is not an isochemical decomposition of ilmenite. In the TiO 2 -FeO-Fe 2 O 3 system (Mg-free), pseudobrookite and titanomagnetite solid solutions do not coexist. However, all three Fe-Ti oxides in the symplectitic assemblage contain significant amounts of Mg. In the TiO 2 -MgO-FeO-FeO 1.5 system at high oxygen fugacities, the Mg-rich pseudobrookite + titanomagnetite assemblage is stable relative to the conjugate pair of Mg-bearing ilmenite solid solutions. At lower f O2 , Fe 2+ increases, Mg/(Mg+Fe 2+ ) (Mg no.) decreases and the conjugate ilmenite pair becomes the stable assemblage at Mg no. < ~0.6. The compositions of coexisting ilmenite + titanomagnetite pairs in the Coleman Pinnacle andesite yield T = 900-1000 °C and f O2 = NNO + 1.5 to + 1.75, one of the highest redox states on record for arc magmas. The calculated fO2 range is consistent with the composition of the ilmenite in equilibrium with pseudobrookite ± rutile and with Fe 3+ -rich cores in hornblende phenocrysts.
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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 | 0.001 | 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".