Strain localization along a detachment system: Deformation of natural dolomitic and calcitic mylonites (Mt. Hymittos, Attica, Greece)
Bibliographic record
Abstract
Carbonate rocks can be thick, mineralogically-homogeneous packages, which accomodate strain in orogenic belts. Despite its contribution to rock strength, the deformation of dolomite as a major rock forming mineral is understudied in comparison to calcite, quartz, and feldspar. We use field, petrographic, and electron back scatter diffraction (EBSD) analyses of dolomitic and calcitic marbles to investigate the response of these rocks to different degrees of strain under greenschist facies. Mt. Hymittos, Attica, Greece, preserves a pair of Miocene top-SSW ductile-then-brittle low-angle normal faults dividing a tripartite tectonostratigraphy. The bedrock of the massif comprises sub-greenschist facies phyllites and marbles in the uppermost hanging wall unit, and high-pressure greenschist facies schists and marbles of the Cycladic Blueschist Unit in the lower two packages. Ductile mylonites in the footwalls of both detachments grade into brittle-ductile mylonites and finally into cataclastic fault cores. The dolomitic and calcitic marbles of the lower units deformed under greenschist facies conditions and their fabrics reflect the relative differences in strengths between these two minerals. In the middle tectonostratigraphic unit, dolomitic rocks are brittlely deformed and calcitic marbles are mylonitic to ultramylonitic with recrystallized grain sizes ranging from 55 to 8 μm. Within the lower package, dolomitic and calcitic rocks are both mylonitic to ultramylonitic with previous P-T data suggesting metamorphism at ~470 °C and 0.8 GPa. EBSD analysis of six dolomitic marbles of the lower unit reveals a progressive fabric evolution from mylonites to ultramylonites reflecting the magnitude of strain and decreasing temperature of deformation. In mylonitic domains, average grain diameters range from 70 to 25 μm. The mylonitic dolomite exhibits low-angle grain boundaries, internal misorientation zones and textures suggestive of subgrain-rotation recrystallization. This mylonitic fabric is crosscut by ultramylonite bands of dolomite with grain diameters of 15 to 5 μm, which overlaps with the dominant grain size of the subgrains formed within the mylonitic domains. In samples closer to the fault core, the ultramylonite fabric is predominant though boudinaged veins, and relict mylonite zones with coarser grains may still be observed. Uniformly ultramylonitic dolomitic marbles exhibit grain diameters of 40 to 5 μm; the majority of grain diameters are less than 15 μm. The ultramylonite bands have low degrees of internal misorientation and an absence of low-angle grain boundaries that, along with correlated misorientation diagrams, suggest the ultramylonitic dolomite grains are randomly oriented and deforming via grain-boundary sliding. Interstitial calcite grains within these samples may reflect creep-cavitation processes interpreted to have occurred syn-kinematically with grain-boundary sliding. The change from subgrain-rotation recrystallization to grain-boundary sliding is interpreted to reflect the interplay of grain-size sensitive and insensitive processes. Following grain size reduction, subsequent deformation was dominantly accommodated by grain boundary sliding. The dolomitic marbles of the lower unit deformed on the retrograde path from the high-pressure, mid-temperature portion of the greenschist facies. The position of the dolomitic ultramylonites immediately below the cataclastic detachment fault suggest these ultramylonites were deforming very close to the brittle-ductile transition suggesting ductile deformation at lower temperatures than might be predicted by deformation experiments.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 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".