Origin of framesite revisited: Possible implications for the formation of CLIPPIR diamonds
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Bibliographic record
Abstract
Framesites are polycrystalline diamonds of enigmatic origin, that differ in numerous respects from mono-crystalline diamond varieties. Their textures suggest rapid crystallization, while the low N-aggregation state of some stones and zoning in some garnet inclusions point to a short mantle residence time and formation broadly coeval with the host kimberlite . This differs from the much older (Archean to Proterozoic) ages of peridotitic and most eclogitic diamonds. In contrast to the rarity (~2%) of websteritic inclusions in mono-crystalline diamonds, a high proportion (> 70%) of garnet inclusions in framesites were previously assigned to a websteritic paragenesis . However, websteritic and megacryst garnets show a marked compositional overlap, making a simple chemical distinction between these two parageneses inconclusive. We highlight several lines of evidence linking framesites and the megacryst suite to a common paragenesis. Crystallization of megacrysts, like that of framesites, was broadly coeval with eruption of the host kimberlite, and some megacryst nodules are characterized by quench textures. Megacrysts are grouped into relatively Cr-rich and Cr-poor sub-populations that may occur within a single hand specimen. Likewise, relatively Cr-rich and Cr-poor garnet inclusions are reported in framesites, occasionally even within the same diamond host. Framesites from individual localities are characterized by closely similar, highly diagnostic C-isotopic signatures, with a majority enriched in 12 C (modal δ 13 C o / oo of −18 to −19) relative to peridotitic and eclogitic diamonds. However, each locality invariably has a sub-population with C-isotopic signatures closer to typical mantle values (−5). Like framesites, large exceptional (CLIPPIR) Type II diamonds from the Cullinan and Letseng kimberlites are dominated by relatively 12 C-rich isotopic signatures, but also include a subordinate population closer to typical mantle signatures (−5). Several lines of evidence are inconsistent with a sub-lithospheric provenance model for these valuable stones. The remarkable similarity of their C-isotopic signatures to those of framesite diamonds points to a common paragenesis, thus also linking them to the megacryst suite. The large size (> 10 mm) of many of the CLIPPIR Type II stones is consistent with such a linkage, as is the evidence that crystallization of CLIPPIR Type II diamonds was broadly coeval with emplacement of the host kimberlite. We present a magmatic model of CLIPPIR diamond crystallization at the low temperature extreme of the megacryst suite, which formed in a pegmatitic vein network surrounding a pooled magma body within the lithosphere. Late-stage (evolved) megacryst magmas would be Ca- and carbonate rich, providing a chemical environment favourable for the crystallization of breyite under lithospheric P-T conditions.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.003 |
| 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 it