Siliceous dolomites in the Horsethief Creek aureole, S.E. British Columbia: fluid infiltration and mineral reactions
Bibliographic record
Abstract
Potassic siliceous dolomites in the Horsethief Creek aureole, S.E. British Columbia, Canada record peak contact-metamorphic conditions of ≈2.2 kbars and 650 °C in the inner aureole. The protolithic dolostones have varying but small amounts of disseminated quartz (≤ 5 volume percent) and K-feldspar (≤15 volume percent) but have interbedded numerous chert nodules and layers. Subvertical joints and veins cut across layering. Six isograds can be identified: phlogopite; tremolite+K-feldspar; diopside; diopside+phlogopite; diopside+dolomite; and at highest grade forsterite. The prevalence of isobarically divariant mineral assemblages, paucity of high XCO2 mineral assemblages, widespread development of hydrous minerals often in high abundance (up to 65 volume percent) and a ≈7 per mill (0/00) depletion (from ≈23 0/00 to ≈16 0/00) in δ18O are all evidence for substantial syn-metamorphic fluid flow. The almost complete de-dolomization of the inner and middle aureole suggests that metamorphism was not isochemical and that silicametasomatism took place. Heterogeneity in the distribution of index minerals and the potassic phases reflect varying bulk composition as well as variable fluid infiltration. Infiltration-driven near-isothermal reactions are documented in the rocks in form of numerous samples showing a texture interpreted to record prograde reaction of diopside to tremolite. A petrographic break is observed at the tremolite+K-feldspar isograd. While rocks up-grade of this isograd are dominated by isobarically divariant assemblages, rocks down-grade are characterized by isobarically univariant assemblages. This break may record a sudden change in infiltration character. The proposed model of contact metamorphism in the impure siliceous dolomites of the Horsethief Creek aureole is: 1) Intrusion of the Horsethief pluton triggered metamorphic reactions in the siliceous dolomites and the underlying pelitic rocks. 2) Buoyant fluids evolving in the metapelites at temperatures >530 °C rose along subvertical joints in and across the different lithologies and infiltrated the dolostone. 3) Infiltration of silica-bearing aqueous fluids triggered pervasive reaction in the siliceous dolomites. Rocks in the outer aureole did not experience significant infiltration because temperatures were too low to trigger the dehydration reaction in the underlying metapelites. Plutonic fluids may only have played a minor role, and bedding parallel flow likely was also only minor.
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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 | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".