It’s on the way up! Syn-exhumation paragenesis of glaucophane-phengite-quartz veins
Bibliographic record
Abstract
Subvertical glaucophane + quartz ± phengite veins exposed in the footwall of a major extensional detachment on southern Evia (NW Cyclades, Greece) record mode-I brittle fracturing with variable principal stress orientations. The dense network of veins displays systematic cross-cutting relationships with a prominent youngest vein set spaced 5-10 cm apart transecting all other veins. Interlayered jadeite-rich metabasalt and quartzite host the veins and promote a pronounced rheological control on fracturing, with veins preferentially hosted in metabasalt layers and terminating abruptly as pressure solution seams or shear bands at contacts with the ductily deformed quartzite. Vein-hosted ferromagnesian minerals do not exhibit recrystallization or dissolution-reprecipitation microstructures. Jadeite in the metabasalt forms both i) 'fuzzy' euhedral crystals overgrown by hematite and ii) symplectitic intergrowths with quartz and albite. Vein-hosted glaucophane and phengite grew at fixed angles (normal and oblique) to vein walls. Phengite is compositionally homogeneous with elevated Si content (3.41–3.52 apfu). Glaucophane from all veins shows a homologous concentric compositional zoning with core chemistry intermediate between glaucophane and magnesioriebeckite, glaucophane-rich mantles, and rims of magnesioriebeckite or winchite. Phengite yields consistent single-grain total-fusion 40Ar/39Ar dates with a weighted mean of 22 ± 1 Ma (n: 22), whereas the low-K glaucophane produced equivocal and dispersed dates. Phengite (n: 44, 20) and glaucophane (n: 8, 42) in-situ 87Rb/87Sr isochrons from two samples yield mutually indistinguishable dates of 21 ± 5 Ma and 25 ± 4 Ma, within uncertainty of the 40Ar/39Ar dates. The uniform mineral chemistry, compositional zoning, and geochronology indicate that the veins formed over a short time without major shifts in ambient pressure-temperature conditions. Contrary to the apparent mineralogically-defined high pressure-low temperature paragenesis of the veins, dates obtained from pristine high-Si phengite support crystallization in the latest Oligocene to earliest Miocene, coincident with regional extension and widespread greenschist-facies retrogradation in the Aegean. Abundant hematite and the predominance of Fe3+-rich sodic amphibole and clinopyroxene species implicates a highly oxidizing fluid in the stabilization of these nominally ‘high-pressure’ minerals under conditions widely responsible for producing retrogradational greenschist-facies assemblages throughout the Cyclades.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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 teacher head, 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".