Fluid-driven low-grade metamorphism in polydeformed rocks of Avalonia (Arisaig Group, Nova Scotia, Canada)
Bibliographic record
Abstract
The Lower Silurian—Lower Devonian Arisaig Group (Antigonish Highlands) in the Canadian Appalachians is a sequence of shallow marine strata deposited after the accretion of Avalonia to Baltica during the closure of the Iapetus Ocean. Deformation of the strata is widely attributed to the Devonian Acadian orogeny and produced shallowly plunging regional folds and a cleavage of varying penetrativity. Phyllosilicate minerals from the finest-grained rocks exhibit very low-grade (diagenetic-anchizone) metamorphic conditions. X-ray diffraction study reveals that the sampled rocks contain quartz, K-white mica, chlorite, and feldspars; illite–smectite and chlorite–smectite mixed-layers are common but Na–K mica and kaolinite occur only in some samples. The identification of illite–smectite mixed-layers in diagenetic samples, with Kübler Index >0.50 Δ°2θ and the highly heterogeneous b -cell dimension of the K-white micas are in agreement with the variable chemical composition of dioctahedral micas, which present low illitic substitution and variable phengitic content. The spatial variation in the above crystal-chemical parameters was plotted along a NW–SE composite cross section across the regional folds. No correlation was found between the metamorphic conditions and either the stratigraphic depth or the strain values measured by phyllosilicates orientation analyses, as a function of the penetrativity of the cleavage. However, the metamorphic grade generally increases towards the Hollow Fault, and is highest in samples located within a 1 km corridor from the fault surface. Incipient cleavage is observed in the anchizonal samples located in the vicinity of the Hollow Fault and in some of the diagenetic samples, indicating cleavage development under low temperatures (<200 ºC). These relationships, together with regional syntheses, suggest low-grade metamorphism post-dated regional folding and was coeval with Late Carboniferous dextral movement along the Hollow Fault. Fluid circulation associated with movement along this major fault may be the driving mechanism for the increasing metamorphism towards it.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".