Mantle roots of major Precambrian shear zones inferred from structure of the Great Slave Lake shear zone, northwest Canada
Bibliographic record
Abstract
Preserved, ancient orogens provide important perspective on modern continental convergent zones. Relatively deep levels of these systems are exposed at the surface, and these crystalline rocks promote the recording of seismic signals from great depths. In this study, multi-azimuthal teleseismic observations reveal gently dipping discontinuities and wedge-shaped structures beneath the Great Slave Lake shear zone, Canada, which formed the Paleoproterozoic convergent boundary between the Archean Slave and Rae cratons during assembly of the Nuna supercontinent. This ancient shear zone experienced two distinct tectonic phases. An early convergence phase involved intracontinental underthrusting of the Slave craton beneath the Rae margin with little evidence of subduction. A later phase was characterized by brittle strike-slip faulting. Receiver functions exhibit discontinuities that imply the latter faults to be listric in the crust. A high-velocity layer below the Moho may mark eclogitic residues of melts that formed "calc-alkaline" granitoids within the crust of the shear zone, without invoking subduction-induced melting within the mantle. Uppermost mantle discontinuities and xenolith suites from nearby kimberlite pipes together define lithological and structural geometries interpreted as two phases of wedging by the central Slave craton lithosphere, associated with either Slave craton construction or early Slave-Rae convergence. The new teleseismic data contain no direct or indirect evidence of faulting along near-vertical suturing structures within the crust or the mantle. The observed wedge-shaped cratonic margins imply that lithospheric blocks grew primarily by lateral accretion of similar blocks, with the strongest layer at 100–150 km depths. In the study area, the diamond-bearing Slave lithospheric mantle wedge underlies the entire shear zone at depths where diamonds are stable, and data indicate that the Slave craton's lithospheric mantle was intact and strong at these depths as early as 2.0–1.9 Ga, when this tectonic boundary was active.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".