Immiscible shoshonitic and Fe-P-oxide melts preserved in unconsolidated tephra at El Laco volcano, Chile
Bibliographic record
Abstract
Abstract The origins of apparently magmatic Fe-P-O deposits like those of the El Laco volcanic complex, Chile, with masses on the order of 1 Gt remain contentious. Previous attention has been focused largely on the high–tonnage massive magnetite bodies that form the economic mineral deposits. Extensive occurrences of unconsolidated granular Fe–P–oxide materials or their apparent metamorphic equivalents have received relatively little attention. Here we report textures and compositions of unconsolidated Fe–P–oxide materials from Laco Sur, El Laco. Unconsolidated tephra at El Laco is dominated by hematite along with subsidiary Fe–phosphates, monazite, and silica. A porous hematite bomb contains menisci of two coexisting materials. One is hydrous shoshonitic glass with perlitic texture, and the other comprises fine-grained intergrowths of Fe–P–REE (rare earth element) oxides having the bulk composition of the eutectic in the system FePO4–Fe2O3 with minor S, Cl, and other components. We show by experiment that very similar compositions would have coexisted as immiscible silicate and oxide liquids at 900 °C and 1 GPa in the presence of carbonic vapor, magnetite, and quartz; both will also form anhydrous liquids at 1080 °C and 101 kPa. We infer the former existence of a phosphatic Fe-oxide magma rich in volatiles that underwent explosive degassing and consequent rapid compositional undercooling to produce the observed assemblage of Fe-oxide tephra containing small amounts of Fe–P–REE phosphates and silicate glass.
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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".