Oxygen isotope systematics of the Precambrian basement of Alberta: implications for Paleoproterozoic and Phanerozoic tectonics in northwestern Alberta
Bibliographic record
Abstract
We have conducted a regional survey of the oxygen isotope compositions of drill core samples from the Precambrian basement of the Alberta sedimentary basin. The majority of samples have whole-rock δ18O (SMOW) values between +7 and +11, as is typical of crustal rocks. However, there are also a significant number of samples with δ18O values less than +5. In these samples, high-grade minerals such as pyroxene, amphibole, and biotite commonly show retrograde alteration to chlorite and (or) epidote. The majority of low-δ18O samples are from a 250 x 50 km zone in northwestern Alberta, which we refer to as the Kimiwan isotope anomaly. The anomaly is significant in that the most reasonable explanation for generating such a laterally extensive zone of rocks, with δ18O values below +5, is through high-temperature interaction with surface-derived fluids in an extensional tectonic setting. We propose, therefore, that the low-δ18O samples define a hitherto unrecognized extensional zone in the Alberta basement. Available geochronological data indicate that fluid-rock interaction and associated 18O depletion occurred at ca. 1800 Ma. Oxygen and hydrogen isotope data on mineral separates from this zone indicate that the surface fluids responsible for 18O depletion were of meteoric origin. Seismic reflection profiles acquired during the Lithoprobe Alberta Basement Transect reveal the presence of basement faults spatially associated with the zone of 18O depletion. We propose that these faults were extensional in nature at ca. 1800 Ma. Periodic reactivation of these basement structures during the Phanerozoic played an important role in the development of faults in the overlying sedimentary basin.
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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 | 0.002 | 0.003 |
| 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) | 0.001 | 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".