Implications for the North American Lower Crustal 7.xx km/s Layer from an Exhumed Crustal Root, Western Canadian Shield
Bibliographic record
Abstract
Studies of the Thorsby magnetic low, the southern extent of the 2,800 km-long Snowbird Tectonic Zone (STZ) in Alberta, Canada, show pronounced lower crustal seismic reflectivity and preservation of a crustal root. These features may be correlative to the well-exposed central STZ, where two lower crustal tectonic events have been identified at 2.6-2.55 Ga and 1.92-1.89 Ga. High-resolution cross-sections of the central STZ reveal the late-stage interaction of Paleoproterozoic intracontinental thrust and strike-slip shear zones responsible for juxtaposing ca. >20,000 km2 of lower continental crust (0.9-1.5 GPa) with middle continental crust (0.5 GPa) (Mahan and Williams, 2005; Dumond et al., 2013). Exhumed crust within the Athabasca granulite terrane (AGT), in northeastern Saskatchewan, revealed that garnet-producing reactions in felsic to mafic granulites resulted in significant densification during long-term lower crustal residence. These reactions provide a viable mechanism for the preservation of crustal roots long after orogeny (Fischer, 2002). This study utilized surface outcrops of mafic granulite and felsic granulite in northern Saskatchewan to test the hypothesis that they represent an exposed record of crustal root development that is presently imaged in the subsurface of Alberta. A georeferenced map and database was compiled that includes topography, aeromagnetic anomalies, and gravity anomalies coincident with the Upper Deck domain of the Athabasca granulite terrane. These data were coupled to phase equilibria modeling of lower crustal bulk compositions to derive a 2-dimensional density and velocity structure of the hypothesized crustal root. The results informed our understanding of how garnet production in lower continental crust influences the stability and isostatic response of continental crust that was thickened and modified during orogeny.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".