Diamonds in cratonic and orogenic settings : a study of Jericho and Wawa diamonds
Bibliographic record
Abstract
Diamonds can form in a number of different ways. Physical and chemical properties of diamonds classify them as formed below cratons (xenocrystal cratonic) or in a subducting slab followed by rapid exhumation (orogenic). I studied diamonds from a cratonic (Jericho kimberlite, Nunavut) and a synorogenic (calc-alkaline lamprophyres of Wawa, Ontario) setting to reconstruct the process of diamond formation. Diamonds from these two locations have been analysed for their morphology, nitrogen content and aggregation, cathodoluminescence, composition of mineral inclusions, and stable carbon isotopes. In addition, fluorescence and stable nitrogen isotopes were studied in Wawa diamonds. Mineral inclusions in Jericho diamonds were compared with diamondiferous and non-diamondiferous eclogitic Jericho xenoliths with respect to major and trace element compositions. The majority of Jericho diamonds belong to “eclogitic” (90% of the studied samples) and “websteritic” (7%) assemblages. The Jericho diamonds differ from “eclogitic” diamonds worldwide in magnesian compositions of associated minerals and extremely light C isotopic compositions (δ¹³C = -24 to -41‰). We propose that metasomatism triggered by H₂O fluids may have been involved in the diamond formation. The model is supported by the general similarity of mineral compositions in diamondiferous eclogites to those in diamond inclusions and to secondary magnesian garnet and clinopyroxene in recrystallized barren eclogites. The ultimate products of the metasomatism could be “websteritic” diamond assemblages sourced from magnesian eclogites. Wawa diamonds show the following features typical for a cratonic origin: 1) weakly resorbed, octahedral morphology; 2) Low N content; 3) high N aggregation state; 4) the mantle signature of carbon isotopes. Other characteristics of the Wawa diamonds suggest a subduction-related origin, i.e. 1) the presence of peridotitic and eclogitic minerals within single diamonds in a mixed paragenesis also combining shallow and deep phases, 2) the crustal signature of nitrogen isotopes. The most viable model to explain the origin of Wawa diamonds involves early subduction of crustal carbon and nitrogen followed by the carbon-bearing mantle metasomatism and advection of the diamondiferous mantle to the shallow depth of the lamprophyre magmagenesis.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".