Petrogenesis of 1.1 Ga carbonatite-kimberlite dykes and sills in the Schreiber greenstone belt, Ontario, Canada
Bibliographic record
Abstract
For the first time, this study presents field relationships, petrographic observations, mineral chemistry, whole rock major and trace element and Sr-Nd and Pb radiogenic isotope geochemistry data for kimberlite, carbonate-rich kimberlite and carbonatite dykes and sills with an estimated age of 1.1 Ga from Ripple Bay, Superior Region, Ontario. An extensive data set was utilized to constrain their petrogenesis and tectonic setting, which has very important implications for the long-standing debate on the co-genetic relationship of kimberlites and carbonatites. Ripple Bay kimberlites, carbonatites, and carbonate-rich kimberlites occur in the same dykes and sills that intrude the Archean Schreiber-Hemlo greenstone Belt. These rocks are divided into three distinct groups based on their carbonate content: 1) kimberlite (carbonate < 20%), 2) carbonate-rich kimberlite (carbonate >20%) and 3) carbonatites (carbonate >80%). Each group also displays a distinctive geochemical affinity. Trace element diagrams of Ripple Bay rocks show distinct negative anomalies of Rb, K, Sr, and Zr-Hf in kimberlites and carbonate-rich kimberlites, whereas carbonatites display negative anomalies in Rb, K, Nb-Ta, Pb, Hf-Zr, and Ti. The REE patterns of Ripple Bay rocks exhibit subparallel trends, with carbonatites displaying the most enriched REE patterns and carbonate-rich kimberlites showing the least enrichment. Ripple Bay rocks have very similar Sr and Nd isotope ratios and major and trace element composition, suggesting a common magma source and petrogenesis. Their geochemical compositions suggest a source that comprises mixtures of MORB-like depleted mantle and an enriched plume source. Ripple Bay rocks do not represent primary magmas because they evolved through fractional crystallization and exhibit crustal contamination. Their geochemistry suggest that the carbonate-rich kimberlites and carbonatites are related by fractional crystallization, whereas their relationship to the kimberlites involves different degrees of partial melting. Their location, geochemical characteristics, field relationships with neighboring rocks, and mineralogy supports their interpretation as 1.1 Ga formations associated with the Mid-continent rift system.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".