Chromian minerals and talc veins in the metasandstones of the Ochi nappe, southern Evia, Greece: The role of fluids in retrograde metamorphism during exhumation
Bibliographic record
Abstract
Unusual minerals were formed during the retrograde metamorphism of high-pressure metamorphic rocks in the Ochi nappe, southern Evia, Greece, specifically widespread sub-mm-scale talc veins and chromian varieties of chlorite, phengite, biotite and allanite. Albite-quartz-calcite and calcite-quartz schists are cut by common 10–200 μm wide veins of talc, rimmed by Cr-chlorite with <0.6 apfu Cr. Hydraulic fracturing by fluids derived from dehydration of subducted chromite-rich serpentinite in the Ochi nappe created fractures in the schists where talc precipitated. Mineral chemistry and textures are related to regional metamorphic and tectonic phases, which included Eocene blueschist metamorphism followed by Oligocene syn-orogenic wedge extrusion. The overprint resulted in retrograde growth of albite porphyroblasts, emplacement of talc veins, and formation of phengite with <0.08 apfu Cr and later biotite with <0.3 apfu Cr. Late Oligocene shearing flattened many pre-existing minerals. Neogene exhumation within the North Cycladic detachment system produced decompression fractures that nucleated precipitation of allanite (some with <0.4 apfu Cr and > 0.8 apfu REE), apatite, titanite and zircon, reflecting the availability of halogen-rich fluids. The evolution of the retrograde metamorphic minerals assemblages can thus be tracked, with pervasive CrMg infiltration in the Oligocene, and more focussed Miocene metasomatism by halogen-rich fluids. [199 words].
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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 | 0.001 |
| Science and technology studies | 0.000 | 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".