Synkinematic growth of tourmaline on brittle-ductile normal faults, Despotiko Island, Aegean Sea, Greece
Bibliographic record
Abstract
Synkinematic tourmaline and quartz growth on slickensides of brittle–ductile normal fault planes was studied by electron-microprobe analysis and X-ray crystallographic methods. The faults show top-to-the-southwest sense of shear and cross-cut mylonitic gneisses of the Cycladic Blueschist Unit on Despotiko Island, located southwest of Antiparos, in the Cyclades, Greece. The black tourmaline crystals, up to 180 μm in length and 50 μm in diameter, form slickenside fibers on these fault planes and therefore have grown during fault slip. They record a chemical variation from X (Na 0.66 Ca 0.20 □ 0.14 ) Y (Fe 2+ 1.17 Mg 0.92 Al 0.78 Ti 4+ 0.12 Mn 2+ 0.01 ) Z (Al 5.00 Mg 1.00 ) (BO 3 ) 3 T (Si 5.95 Al 0.05 )O 18 V (OH) 3 W [(OH) 0.88 F 0.12 ] to X (□ 0.50 Na 0.48 Ca 0.02 ) Y (Fe 2+ 1.75 Al 1.31 Mn 2+ 0.02 Ti 4+ 0.01 ) Z (Al 5.49 Mg 0.51 ) (BO 3 ) 3 T (Si 5.98 Al 0.02 )O 18 V (OH) 3 W (OH). The tourmaline compositions belong to the foitite – schorl – dravite series. On the basis of X □− X Mg , X □−Ca, Ca– X Mg relationships and significant chemical differences between analogous and antilogous poles, these tourmalines most likely grew at low- to medium-grade metamorphic conditions, corresponding to crystallization temperatures between 300 and 400 ± 50°C. This is consistent with the low amounts of [4] Al and F in these tourmalines, the observation of almost completely chloritized biotite near the slickensides, and the deformation microstructures of quartz in the fault. Together with structural measurements in the field, these data suggest that the tourmaline slickenside fibers crystallized during a late stage of overall NE–SW-oriented extensional exhumation, bringing the rocks from lower-greenschist facies conditions to the brittle–ductile transition zone.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".