Trace elements concentrations in apatites from the Sept-Îles intrusive suite – implications for the genesis of nelsonites
Bibliographic record
Abstract
Cumulates of apatite and Fe-Ti oxides are form during the later stages of crystallization in many layered intrusions. In some cases they occur as layers or lenses of nelsonite composed of about one third of apatite and two thirds of Fe-Ti oxides. Associated with nelsonite are troctolite or diorite enriched in oxides. Two different models have been proposed for the origin of these rocks. Both models suggest that a Fe-Prich silicate liquid formed after considerable crystal fractionation of the mafic parental liquid. In the first model, Fe-Ti-oxide and apatite crystallize from this magma and accumulate on the crystal pile to form nelsonite. In the second model the silicate liquid splits into; a) an Fe-Ti-P liquid from which nelsonite forms and b) a SiO2-rich liquid. \n \nWe have investigated the whole rock and mineral compositions of nelsonites and associated rocks from the Sept- Îles Intrusive Suite, Quebec. In addition, we have determined the trace element concentrations of apatite in these rocks. Mass balance calculations show that apatite is the principle host for REE, Ca, U, Th and Sr in these rocks. To test the crystal accumulation model these trace elements were inverted to estimate the trace element composition of the magma at the time of apatite saturation. Mantle normalized trace element patterns of the estimated liquids are similar in shape to mantle normalized patterns from dykes believed to be feeders to the intrusion at this stratigraphic level. Apatite would not have been on the liquidus of magmas of the dyke compositions. A simulation (using PELE) was carried out in order to model crystallization of a magma derived from the dykes. The model mineral compositions and the trace element patterns including those of apatite match the observed compositions for Sept-Îles nelsonites and associated rocks. Thus we favour the crystal accumulation model for the formation of nelsonite and associated rocks.
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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 | 0.000 |
| 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".