Bibliographic record
Abstract
Archean cratons are comprised of thick, stable continental lithosphere that has persisted for billions of years owing to their isopycnicity (i.e. near neutral buoyancy) and higher viscosity than the surrounding mantle. These regions host diamonds at depths greater than 150 km due to the relatively cold temperatures found in the depth range where pressure is high enough for diamonds to be stable. Because of this, understanding the deep structure of cratonic lithosphere is important for regional diamond exploration. In this thesis previously collected magnetotelluric (MT) data were used to produce a 3-D resistivity model of the Slave craton's lithosphere. The resolution of this resistivity model was rigorously tested. Important features of the model and their implications include: (1) A region of low resistivity (< 10 Ωm) at a depth of 100 km beneath the Lac de Gras kimberlite field in the central Slave craton, which was interpreted as a layer of high density saline fluids that were emplaced from a Mesozoic subduction event. Phlogopite and grain boundary sulphides also remain as possible interpretations for the cause of the low resistivity (< 10 Ωm). However, none of these proposed interpretations are without their flaws. Fluids in the mantle would be positively buoyant and reactive suggesting that it would be difficult to retain fluids from the Mesozoic over long time periods. Large quantities of phlogopite would be required (> 20% volume fraction) to produce the low resistivity observed (< 10 Ωm), which is not strongly supported by observations in xenoliths and there is little experimental work on grain boundary sulphides in the mantle. This region of low resistivity was previously observed at depths of 80 - 120 km by Jones et al. (2003). Previous interpretations of this conductor invoked graphite films as an explanation, but it is unlikely that graphite films are stable at these depths. The spatial correlation between the low resistivity layer and the Lac de Gras kimberlite field could be the result of kimberlite magmas following zones of weakness in the lithosphere as a result of the metasomatism caused by the slab-derived fluids. (2) The resistivity model also showed that beneath the entire Slave craton the lithosphere-asthenosphere boundary (LAB) is at a depth of at least 200 km. Determining the depth to the LAB is important as this can determine the size of the diamond stability field within the lithosphere, which is used in regional diamond targeting. (3) The upper mantle resistivity can be interpreted as requiring a low water content on the order of 10 - 150 ppm by weight in the depth range 100 -170 km. Below these depths the lithosphere appears to be dry (< 5 ppm). The dry base of the lithosphere may act as a resistant boundary preventing the cratonic root from being eroded by the underlying asthenosphere.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| 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".