Origin of megacrysts by carbonate-bearing metasomatism: a case study for the Muskox kimberlite, Slave craton, Canada
Bibliographic record
Abstract
Low-Cr and high-Cr clinopyroxene, garnet, olivine and ilmenite megacrysts from the Muskox kimberlite (Canada) were analysed for major and trace elements, as well as Sr, Nd and Pb isotopes. Samples display compositional overlap with respective phases in websterites, and clinopyroxene isotope systematics reveal similarities to both websteritic and metasomatic clinopyroxene in peridotites from the same kimberlite, in addition to Muskox and Jericho kimberlites. All lithologies may represent the products of mixing between EM1 mantle, relict Proterozoic enriched mantle and HIMU carbonatitic fluid. Equilibrium melts calculated from clinopyroxene trace element data using experimental distribution coefficients for feasible proto-kimberlitic melts yield a range of metasomatic agents. Conclusion on the carbonate-bearing nature of the metasomatism is based on the presence of a HIMU isotopic signature and results obtained from thermodynamic modelling using the Deep Earth Water model. Modelling was carried out with three fluid compositions; asthenospheric, eclogitic and kimberlitic. Our results suggest mineral compositions analogous to megacrysts cannot be produced by metasomatism of mantle peridotite by carbonate-free hydrous fluids. Isotope systematics argue against a strictly cognate relationship between megacrysts and their host kimberlite, instead suggesting that megacrysts and websterites may represent products of regional metasomatism by carbonatitic HIMU fluids shortly predating kimberlite magmatism. Supplementary material: A table containing parameters used in isotopic mixing models is available at https://doi.org/10.6084/m9.figshare.c.5255825
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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 | 0.002 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".