The origin of compositional variations in kimberlites based on comparative petrology and geochemistry of samples from four cratons
Bibliographic record
Abstract
Abstract The term ‘kimberlite’ describes rocks that span a large mineralogical variety including enrichments in mica, carbonates, perovskite, spinel and/or ilmenite. The origin of these compositional variations is addressed here by comparing the petrography, mineral chemistry and bulk-rock as well as groundmass geochemistry of seven representative kimberlite samples (from Wesselton in South Africa; Karowe in Botswana; Diavik and Gahcho Kué in Canada; Majuagaa in Greenland, and Letšeng in Lesotho). These samples exhibit a broad range of mineral and bulk geochemistry covering the whole kimberlite spectrum. Bulk-groundmass compositions are variously enriched in Si, K, Ti, CO 2 and H 2 O depending on the dominant groundmass mineralogy – e.g., high K in mica-rich samples. Interaction with mica and ilmenite-bearing lithospheric mantle appears to be the driving factor of K (± Al) and Ti enrichment, respectively. Degassing controls CO 2 , and higher SiO 2 in the melt derived from assimilation of lithospheric pyroxenes leads to a decrease in CO 2 solubility. Serpentinization by deuteric and/or crustal fluids governs H 2 O concentrations, generally exceeding the H 2 O solubility in kimberlitic melts at upper crustal conditions. Even where the groundmass composition closely approximates predicted kimberlitic melts such as at Majuagaa, the low contents of Na require substantial loss of alkalis via fluids during ascent and emplacement. Thus, compositional variations in erupted kimberlites reflect the combination of asthenospheric source variability, lithospheric assimilation, crystallization, degassing and interaction with deuteric and crustal fluids.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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 teacher head, 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".