Reconstructing the nature of the metamorphic basement in the Cyclades, Greece, by the isotopic signature of hydrothermal minerals
Bibliographic record
Abstract
In complex continental back-arc settings, such as the Cycladic realm of southeast Greece, polymetallic mineralization can provide information about past tectonic events and help to reconstruct the architecture of the metamorphic basement. In the Cyclades archipelago, slab rollback generated Miocene crustal extension and the formation of metamorphic core complexes, where hydrothermal systems occurring in the upper crust track one of the latest events in the geodynamic evolution. Lead isotope ratios of galena (PbS) and Sr isotope ratios of barite (BaSO4) of the polymetallic ore deposits, which are exposed on most of the islands, reveal two distinct sources of lead and strontium in the underlying basement of the core complexes. A clear division exists between 206Pb/204Pb≤18.84 and 87Sr/86Sr≥0.711 in the north-central Cyclades and 206Pb/204Pb≥18.84 and 87Sr/86Sr≤0.711 in the west Cyclades. This regional pattern corresponds with the exposures of the high-pressure/low-temperature Upper and Lower Cycladic Blueschist nappes on the islands, respectively. Moreover, the pattern follows the surface trace of the proposed synorogenic Trans-Cycladic Thrust, a subduction-related structure that imbricated the high-pressure units. In addition, the isotopic composition of the hydrothermal minerals indicate that the structurally lower Cycladic Basement has a stronger influence on the metal sources of deposits occurring in the hanging wall of the Trans-Cycladic Thrust than in the footwall. Observations featuring the isotopic signature of hydrothermal minerals are complemented by a compilation of new and published isotopic and geochemical whole-rock data of the basement rock types. This allows us to further interpret the geodynamic significance of the apparent heterogeneities in the exposed rocks of the metamorphic core complexes and correlate the scattered exposures of the metamorphic basement. Furthermore, regional patterns in the isotopic and geochemical signature of the basement lithologies help to reconstruct the nature of the continental margin prior to Cretaceous-Eocene subduction.
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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 | 0.000 |
| 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".