Olivine diversity in the Leslie kimberlite, NT, Canada : implications for transport and emplacement processes
Bibliographic record
Abstract
Olivine crystals are ubiquitous in kimberlites and record petrologic events through all stages of ascent and eruption. Well-preserved olivine from the Leslie kimberlite, NT, Canada elucidates the sequence of events attending kimberlite emplacement. The Leslie kimberlite mainly hosts a single phase of extrusive coherent kimberlite. We used spatially distributed samples (n = 76) from drill core to develop a 3D representation of the Leslie kimberlite. Petrographic investigation defined four distinct olivine populations: phenocrysts, macrocrysts, dunite “nodules”, and mantle xenolith-hosted olivine. SEM imagery, and major and trace element geochemistry were used to characterize and quantify chemical zonation including xenocrystic cores, mid-zones, magmatically crystallized rims, high-Mg rinds, and/or monticellite coronas. Core compositions (Fo85.7 to Fo93.8, NiO ~0.36 wt%) and other textural evidence show that cores are mantle-derived olivine xenocrysts. Mid-zones developed on cores show a sharp decrease in Fo content (~Fo90.9) across irregular, convoluted, and embayed contacts indicating disequilibrium and partial dissolution of the olivine xenocrysts combined with diffusion-driven replacement. Magmatically crystallized olivine rims can jacket xenocrystic cores and mid-zones. Rims have uniform and distinctive chemical compositions of ~Fo91.8 ± 0.7 (2σ) and NiO concentrations that decrease (~0.4 wt% to ~0.1 wt%) outward. Rinds, thin outer fringes, have a convoluted inner contact and a sawtooth contact with the groundmass. Rind compositions have high ~Fo97.1, low NiO, and elevated Mn and Ca. Rind textural relationships and compositions suggest a non-magmatic, post-emplacement origin. The four olivine populations and chemical zonation (only cores, mid-zones, and rims) are uniformly and consistently distributed throughout the Leslie kimberlite. Thus, olivine within a single phase of kimberlite predominantly records pre-emplacement processes and illustrates that magma batches become well mixed during ascent and emplacement. In contrast, both late-stage high-Mg rinds and monticellite coronas are non-uniformly distributed throughout the pipe. Utilizing olivine geochemistry, coupled with petrographic observations, we reconstruct a sequence of events of the Leslie kimberlite ascent and eruption. Our results indicate olivine entrainment and ascent (within a single kimberlite phase) may be sufficiently characterized by a few samples. Conversely, syn- and post-emplacement processes recorded by olivine require systematic sampling to capture all potential heterogeneities within a given kimberlite phase.
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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 | 0.001 |
| 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 | 0.002 | 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".