MINERAL EQUILIBRIA IN QUARTZ LEUCOAMPHIBOLITES (QUARTZ - GARNET - PLAGIOCLASE - HORNBLENDE CALC-SILICATES) FROM SOUTHEASTERN BRITISH COLUMBIA, CANADA
Bibliographic record
Abstract
Pods and lenses of leucoamphibolite a few meters in maximum dimension contain quartz (Qtz) ‐ plagioclase (Pl) ‐ hornblende (Hbl) ‐ garnet (Grt) ‐ epidote (Ep), with or without biotite (Bt). They occur within Late Precambrian clastic metasedimentary rocks of the Esplanade Range of southeastern British Columbia, and range in metamorphic grade from upper biotite zone to kyanite (Ky) zone (defined in pelitic rocks). Mineral equilibria using the database of Berman provide estimates of metamorphic pressure (P), temperature (T), and fluid compositions. These estimates can be compared to those from coexisting pelitic rocks to provide a check on consistency. Grt‐Bt Mg‐Fe exchange geothermometry suggests temperatures ranging from 530 to 580°C at 7 kbar. The lack of kyanite in leucoamphibolites suggests a maximum P of about 7‐8 kbar. Pl‐Qtz‐Ep‐Grt assemblages without calcite suggest H2O-rich fluid compositions [generally X(H2O) > 0.8]. For a(H2O) = 1.0, Grt‐Ep‐Pl‐Qtz‐ H2O equilibria produce calculated temperatures near 565 °C at 7 kbar. Although there is considerable overlap, estimates of P and T from the leucoamphibolites do not agree very well with estimates from nearby pelites. On the basis of natural occurrences, ot her investigators have suggested a miscibility gap and near-constant activity of anorthite over the range An 40‐90. Electron-microprobe spot analyses in our study indicate that plagioclase compositions near ~An 40 and ~An90 occur within single grains and within single samples. Other samples have compositions concentrated near either An 40 or An90 or compositions with An≤40. These results are consistent with petrological studies reported by other researchers.
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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 | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".