Structural Analysis of a Potential Peri-Gondwana Detachment: George River Suite-Bras d’Or Gneiss Contact Relations in the Creignish Hills, Cape Breton, Nova Scotia
Bibliographic record
Abstract
Late Neoproterozoic ductile shear zones that juxtapose low-grade over high-grade assemblages are characteristic features of parts of the peri-Gondwanan terranes of the Canadian Appalachians.One such ductile shear zone, in the Creignish Hills of Cape Breton Island, Nova Scotia, brings low-grade platformal metasedimentary rocks of the George River Suite into contact with underlying high-grade rocks of the Bras d'Or Gneiss.The low-grade assemblage includes quartzite, marble, schist and phyllite with interlayered felsic volcanogenic units and mafic flows, whereas the high-grade unit comprises low-pressure, high-temperature gneisses and migmatites, including pelitic paragneisses of likely volcanogenic origin.The contact between the two assemblages is defined by a broad mylonite zone that envelopes the high-grade rocks in the form of a WNW-plunging antiform.The structural dome is in fault contact with Carboniferous strata to the east and south, and is unconformably overlain to the north.Kinematic indicators within the mylonites, including asymmetric porphyroclasts, fractured veins, S-C fabrics and folded mylonitic foliation, suggest a broadly top-to-the-southeast (dextral) sense of shear, while the presence of gneissic granitoid sheets that are broadly concordant but locally cross-cut and are folded about the mylonitic foliation, suggest that mylonitization was accompanied by partial melting and syntectonic intrusion.Monazite from the gneisses and zircon from the granitoid sheets have yielded near-identical U-Pb crystallization ages of ca.550 Ma.Juxtaposition of low-grade over high-grade assemblages in several peri-Gondwanan basement blocks in central Cape Breton Island suggests that the folded ductile shear zone exposed in the Creignish Hills is part of a regional low-angle detachment.Similar ductile shear zones with easterly components of shear and low-angle pre-Carboniferous orientations also place low-grade over high-grade rocks in southern New Brunswick and the Cobequid Highlands of mainland Nova Scotia.Dated at ca. 565-540 Ma and ca.605 Ma, respectively, they suggest repeated late Neoproterozoic detachment within the peri-Gondwanan arc.In the Cobequid Highlands, detachment was synchronous with arc magmatism and has been attributed to pull-apart basin development in response to oblique subduction.In southern New Brunswick and Cape Breton Island, detachment broadly coincides with the termination of arc magmatism and may reflect diachronous ridge-trench collision.
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".