Origin of vein-graphite derived from metamorphic fluids in Moine (Glenfinnan Group) rocks, NW Scotland
Bibliographic record
Abstract
Synopsis Proterozoic metasediments at Glen Strathfarrar, Inverness-shire, host a deposit of vein-graphite that is unique within the Moinian stratigraphic sequence. Carbon isotopic analysis, Raman microspectroscopy, fluid inclusion studies and volatile gas analysis were used to constrain the origin of the vein-graphite. Carbon isotopic analysis shows that the carbon is heavier than that expected for sedimentary material (δ 13 C value of −14.35‰), suggesting that fractionation has taken place since sedimentation. Graphitization of sedimentary carbon in the Glenfinnan Group pelitic gneiss occurred in response to changes in both temperature and pressure arising from a series of regional metamorphic events. Scavenging of carbon by metamorphic fluids generated during amphibolite-grade metamorphism associated with the youngest, possibly Caledonian, event is the most probable source of the vein-graphite at Glen Strathfarrar. Similarities in gas composition with quartz veins occurring in Dalradian rocks show that carbonaceous sedimentary sequences consistently generate fluids rich in CO 2 and N 2 , making volatile gas analysis a valuable tool in determining the history of metamorphic fluids. The occurrence of crystalline graphite in the pelitic gneiss at Glen Strathfarrar makes it highly likely that the carbon-rich fluids have been generated from within the Glenfinnan Group sediments rather than from Lewisian rocks at depth. Despite the assertion that graphite is uncommon in Moine rocks, the high ammonium content of biotite in these metasediments and the consistently high N 2 values of fluid inclusions within the siliceous schist and quartz veins suggest that, prior to metamorphism, the sediments contained more organic matter than their present composition suggests. Supplementary material: The results of incremental crush analysis of vein samples from localities within the Moine, Dalradian and Old Red Sandstone are available at http://www.geolsoc.org.uk/SUP18499 .
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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 | 0.001 | 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".