Proterozoic tectonic accretion and growth of western Laurentia: results from Lithoprobe studies in northern Alberta
Bibliographic record
Abstract
The western Canadian Shield of northern Alberta is composed of a series of continental slivers that were accreted to the margin of the Archean Rae hinterland ca. 1.92.0 Ga., preserving a unique record of continental evolution for the interval 2.12.3 Ga. This part of Laurentia owes its preservation to the accretionary style of tectonic assembly south of the Great Slave Lake shear zone, which contrasts with indentationescape processes that dominate the Paleoproterozoic record farther north. The Buffalo Head and Chinchaga domains form the central core of this region, comprising a collage of ca. 23252045 Ma crustal elements formed on an Archean microcontinental edifice, and similar age crust is preserved as basement to the Taltson magmatic zone. The distribution of magmatic ages and inferred collision and subduction zone polarity are used to indicate closure of intervening oceanic basins that led to magmatism and emplacement of continental margin arc and collisional belts that formed from ca. 1998 to1900 Ma. Lithoprobe crustal seismic profiles complement the existing geochronologic and geologic databases for northern Alberta and elucidate the nature of late stages of the accretionary process. Crustal-scale imbrication occurred along shallow eastward-dipping shear zones, resulting in stacking of arc slivers that flanked the western Buffalo Head terrane. The seismic data suggest that strain is concentrated along the margins of these crustal slivers, with sparse evidence for internal penetrative deformation during assembly. Post-collisional mafic magmatism consisted of widespread intrusive sheets, spectacularly imaged as regionally continuous subhorizontal reflections, which are estimated to extend over a region of ca. 120 000 km2. The form of such mid-crustal magmatism, as subhorizontal sheets (versus vertical dykes), is interpreted to represent a style of magma emplacement within a confined block, for which a tectonic free face is unavailable.
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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 | 0.003 | 0.004 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".