Bibliographic record
Abstract
Carbonated mantle is widely considered a significant source for many alkaline magmas, yet carbonate minerals are rarely preserved in mantle samples due to their tendency to volatilize under typical magmatic and surface conditions. Here, we report the first occurrence of mantle-equilibrated (“primary”) carbonate within spinel peridotite xenoliths from the Pacific Coast Ranges in North America. The xenoliths are hosted in a 19 Ma basanite dyke near the boundary between the Intermontane and Coast Belts of the Canadian Cordillera (Mt. Preston, British Columbia). Magnesian calcite (Ca ratio ~0.90) occurs in all samples as: i) intergranular grains in textural equilibrium with surrounding minerals (granoblastic texture, 0.4 mm grains; < 2 vol%), ii) inclusions within mantle silicates; and as iii) intergranular or fracture-filling veins. Sulphides (pentlandite and chalcopyrite), also occur in equilibrium with the carbonate. Geothermometry on carbonate-bearing mantle xenoliths record paleo-equilibrium temperatures of ~815 to 1120 °C, corresponding to depths of ~32 to 55 km on a model geotherm for warm, thin Cordilleran-style lithosphere. Bulk-rock C–O isotopes of the xenolith suite vary as δ13C = -3 to -6, and δ18O = 10 to 12. Collectively, the textural, geochemical and isotopic evidence suggest that a carbonate melt with associated monosulphide solution metasomatized and enriched previously depleted mantle lithosphere. The metasomatic fluids sourced from the subduction of oceanic crust beneath North America during Coast Plutonic Belt magmatism when Mt. Preston was in an arc to back arc position. The host basanite dyke contains magmatic groundmass calcite (δ18O = 14±, δ13C = -4±, 87Sr/86Sr = 0.7040±) indicating a high intrinsic PCO2 that inhibited thermal decomposition of mantle carbonate within the xenoliths during ascent.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.004 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
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".