Kimberlite emplacement conditions through experimentally produced reaction rims on ilmenite macrocrysts
Bibliographic record
Abstract
Abstract Kimberlites, the primary hosts of diamond deposits, are enigmatic igneous rocks derived from the mantle and emplaced into ancient cratons. However, the nature of the primary kimberlite melt remains a subject of debate, limiting our understanding of ascent and emplacement processes. This study aims to enhance our understanding of kimberlite crystallization and emplacement by focusing on the mantle-derived oxide minerals entrained within kimberlites during their ascent. These mantle minerals, which are in disequilibrium with the kimberlite magma, develop various reaction textures, including secondary rims. Natural kimberlite samples show ubiquitous reaction rims on ilmenite, with mineral compositions, particularly Ti-bearing phases (i.e., perovskite, titanite, or anatase), varying across different kimberlite lithologies. To investigate the effect of kimberlite crystallization conditions on the stability of ilmenite, textures, and composition of the reaction rims, we conducted experiments in a piston-cylinder apparatus at 1050–1200 °C and 0.5–2.5 GPa using natural ilmenite grains and synthetic kimberlite melts with varying SiO2/CaO ratios. Our experiments revealed that ilmenite dissolution in kimberlitic melts consistently produced rims of perovskite around ilmenite. Titanite appeared only when at least 6 wt% of granodiorite was added to a kimberlite composition, representing assimilation of crustal rock by the kimberlite magma. Additionally, lower water content affecting the degree of melting favored the stability of Ti-bearing phases (perovskite and titanite) to higher temperatures. Our results confirm that reaction rims on ilmenite form during the magmatic stage of kimberlite emplacement at temperatures of 1050–1200 °C and depths corresponding to 15–75 km (0.5–2.5 GPa), in agreement with the previous estimates for kimberlite crystallization temperatures. We demonstrate that the presence of titanite in the rims of ilmenite from some diatreme volcaniclastic kimberlite lithologies is an indicator of crustal assimilation.
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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 | 0.001 |
| 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) | 0.002 | 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".