Exhumation of Eocene high-pressure metamorphic rock by coaxial flattening below a Miocene Cycladic-style detachment
Bibliographic record
Abstract
Structures that accommodate extension during orogenic relaxation significantly modify the crustal architecture of mountain belts. Discerning the tectonic significance of superimposed structures relating to extensional overprint of initially compressional features is therefore critical to the reconstruction of an orogen, and is easiest where the large-scale mechanical interactions between different crustal domains are exposed. In the Aegean region of Greece, low-angle detachment faults of early Miocene age were partially responsible for exhuming Eocene high-pressure, low-temperature (HP-LT) metamorphic rocks of the Cycladic Blueschist Unit (CBU). Extension in the Cyclades commonly occurred along multiple detachment branches at the kilometer scale, either due to arrest of older detachment planes by late Miocene plutonism, or because strain partitioning along multiple, simultaneously active structures was rheologically favourable. We document a third plausible mechanism whereby crustal attenuation is accomplished via distributed coaxial strain in the footwall of a major detachment, described previously in the Cyclades primarily for deep crustal fabrics contemporaneous with peak HP-LT conditions. This style of deformation is recorded below the basal contact of the CBU on the island of Evia, which delineates the boundary of a major tectonic window exposing an underthrust external carbonate platform known as the Basal Unit (locally Almyropotamos Unit). New structural observations, complemented by white mica 40Ar/39Ar and zircon (U-Th)/He ages, suggest that the upper structural levels of the Basal Unit accommodated flattening strain that coincided with Oligo-Miocene extension likely related to the overlying North Cycladic Detachment System. Vertical shortening, with extension in both other principal directions, is evinced by symmetric chocolate-tablet foliation boudinage and conjugate shear bands in the Basal Unit, alongside coeval type-3 refold structures in the overlying CBU. Pseudosection modelling results from Evia further corroborate a late greenschist-facies (320 ± 40 °C, 7 ± 1 kbar) paragenesis for the fabric associated with this extension that post-dates HP-LT metamorphism. Our observations indicate extrusion of the CBU and underlying Basal Unit was accomplished at least in part by coaxial vertical shortening, in contrast to the predominantly non-coaxial strain observed in the footwalls of other major Cycladic detachments.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".