Low heat flux and large variations of lithospheric thickness in the Canadian Shield
Bibliographic record
Abstract
Ten new heat flux determinations have been made using measurements in 22 mining exploration boreholes located at latitudes higher than 51°N in the Canadian Shield. They provide data in poorly sampled regions near the core of the North American craton where one expects the lithosphere to be thickest. The new heat flux values are all smaller than 34 mW m −2 and are among the lowest recorded so far in the shield. For all the new sites, there is no relationship between heat flux and heat production in surface rocks. In the Canadian Shield, heat flux variations occur at wavelengths <100 km and are mostly of crustal origin. Local averages in two 250 × 250 km windows located on Archean areas at high latitudes on either side of James Bay are 29 mW m −2 and 31 mW m −2 , the lowest values found so far at this scale in the Canadian Shield. S wave traveltime delays derived from tomographic models provide the additional constraints needed to resolve differences of deep lithospheric thermal structure. There is no significant correlation between average surface heat flux and traveltime delays within the Canadian Shield, confirming that variations of the surface heat flux are mostly of crustal origin. Traveltime delays cannot be explained by variations in crustal heat production only and require variations of heat supply to the lithosphere and/or radiogenic heat production in the lithospheric mantle. These variations are associated with changes of lithospheric thickness that may be as large as 80 km. The heat flux at the base of the Superior lithosphere is constrained to be 11 ± 2 mW m −2 .
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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 | 0.002 | 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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".