A (tectonic) window of opportunity: crustal architecture and low-temperature geochronology of the NE Attica Peninsula, Greece
Bibliographic record
Abstract
Miocene extension and crustal thinning in the Aegean were largely accommodated by a bivergent detachment system. The region contains several metamorphic core complexes that have overprinted Eocene high-pressure, low-temperature (HP-LT) metamorphic rocks of the Cycladic Blueschist Unit (CBU). The Attica Peninsula, along the northern margin, hosts the lateral termination of one of the major detachments, the SW-directed West Cycladic Detachment System (WCDS). Moreover, NE Attica has long been thought to contain a large tectonic window exposing the structurally lowest unit of the Attic Cycladic Belt, the Basal Unit. Our new mapping reveals that NE Attica primarily consists of a NE-dipping tectonic nappe of greenschist-retrogressed, HP-LT units, of probable Late Triassic to Late Cretaceous origins. In the west, Upper Cretaceous low-grade or non-metamorphosed units are juxtaposed above the nappe by a NNE-SSW striking, top-to-SW detachment fault. In the east, a package of HP marbles, evinced by calcite pseudomorphs after aragonite, lie above the nappe along a newly discovered NE-dipping fault, the Marathon Thrust. The common footwall of both structures includes isoclinally folded marbles and schists resulting in an apparent map-scale repetition of units. Schists are variably quartzitic to calcitic and contain intercalations of quartzites, metabasites, marble mylonites and, near the stratigraphic top, blue-grey marble. Axial planes of Dn recumbent isoclinal folds (Fn) develop a pervasive, gently NE-dipping Sn foliation (~320°/30°). Syn-metamorphic Fn axes have the same orientation as a NE-SW mineral and stretching lineation (Ln; from 050° to 100°) that forms along the Sn planar fabric. Ln plunges dominantly towards the NE with some variation from subsequent Dn+1 folding. The cooler Dn+1 event is recorded by SW-vergent folds with NW-SE striking Fn+1 axial planes that form an Sn+1 crenulation cleavage, locally defining the main foliation. NW-SE trending Fn+1 axes are parallel to an Ln+1 intersection lineation. Winged inclusions, flanking folds and domino boudinage of dolomite layers within calcitic marbles indicate top-to-SW sense of shear under ductile to brittle-ductile conditions. White mica 40Ar/39Ar (MAr) dates throughout the footwall are earliest Miocene and zircon (U-Th)/He (ZHe) ages are middle Miocene. A several m-thick fault gouge separates the footwall from low-grade metasandstones, limestones and serpentinite bodies in the detachment hanging wall. A narrow zone (10 m) in the immediate hanging wall contains Na-amphibole-rich schists and metabasic blocks with a different HP-LT record than the footwall. MAr dates from the hanging wall are Permian to middle Cretaceous and ZHe dates are early Eocene to middle Miocene. The geochronology from the footwall suggests coeval deformation with the CBU footwall of Mt. Hymittos and correlates the dominant top-to-SW detachment on NE Attica with the WCDS exposed at Mt. Hymittos and S Attica. Together with regional lithostratigraphic correlation, we propose the dominant nappe of NE Attica is CBU, specifically Lower Cycladic Blueschist Nappe, with Pelagonian Zone in the detachment hanging wall. Our reinterpretation is coherent with the classic Cycladic detachment architecture, and consequently limits the exposure of the Basal Unit to the easternmost marble thrust nappe on NE Attica and the Almyropotamos window on Evia.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".