Crystallization of megacrysts by carbonatitic metasomatism : evidence from the Muskox kimberlite, Nunavut, Canada
Bibliographic record
Abstract
Low-Cr and high-Cr clinopyroxene, garnet, olivine, and ilmenite megacrysts from the Muskox kimberlite (Nunavut, Canada) have been analyzed for major and trace elements, as well as Sr, Nd and Pb isotopes in an attempt to constrain the debated origin of the kimberlitic megacryst suite. Samples display compositional overlap with respective phases in websterite, while clinopyroxene Sr-Nd-Pb isotope systematics reveal similarities with both websteritic clinopyroxene and metasomatic clinopyroxene in peridotites from the same kimberlite, in addition to whole-rock isotope data for the Muskox and neighboring Jericho kimberlites. All studied lithologies may represent the products of mixing between EM1 mantle, locally restricted relic Proterozoic enriched mantle and HIMU carbonatitic fluid. Equilibrium melts calculated using clinopyroxene trace element data reaffirm a carbonatitic affinity of the metasomatic agent. Thermodynamic modeling using the Deep Earth Water model shows that megacryst mineral compositions cannot be produced through metasomatism of mantle peridotite by H₂O-rich kimberlitic, asthenospheric or eclogitic fluids. The Sr-Nd-Pb isotope systematics argue against a strictly cognate relationship between Muskox megacrysts and the host kimberlite. Our findings rather suggest megacrysts and websterites represent products formed through regional metasomatism by carbonatitic HIMU fluids that predate kimberlitic magmatism.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 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".