PROVENANCE OF A POLYDEFORMED METASEDIMENTARY SUCCESSION ON THE CANADIAN SHIELD: INSIGHTS FROM NEW U-PB, HF, AND O ISOTOPE ANALYSIS OF DETRITAL ZIRCON FROM THE PALEOPROTEROZOIC MURMAC BAY GROUP
Bibliographic record
Abstract
The proximity and positions of the cratons that make up the Canadian Shield prior to and during the Rhyacian Period (2.30-2.05 Ga) are poorly known. The position of the Rae craton relative to the now proximal Slave, Hearne, and other microcontinents, such as the Buffalo Head-Chichaga domains, during this time period is not well defined. This is due in part to their boundaries having been overprinted by younger orogenic events. Sedimentary successions deposited near craton margins provide an opportunity to test hypotheses regarding nearest cratonic neighbors during deposition by reconstructing their sedimentary provenance using detrital zircon isotopic data. The polydeformed nature of the Murmac Bay Group, a metasedimentary succession deposited near the southwestern margin of the Rae craton in northern Saskatchewan, Canada, presents challenges in determining detailed stratigraphic relationships in the upper succession, which lacks distinct marker beds. Presented here is the first integrated detrital zircon U-Pb geochronology, Lu-Hf, and O isotope analysis of detrital zircon from these rocks in order to elucidate provenance, basin tectonic setting, and characterize crustal growth in the source regions. Previous U-Pb geochronology suggests the lower succession was deposited <2.32 Ga and the upper succession between <2.17 Ga and >1.93 Ga. New U-Pb detrital zircon ages for the upper succession define a new maximum depositional age constraint at <2.00 Ga. Analysis of published U-Pb detrital zircon age spectra suggest the tectonic setting for the upper Murmac Bay Group paleobasin was in the foreland of the Taltson orogeny. Integrating the U-Pb data with new Lu-Hf and O isotope data shows that the most probable source rocks, in addition to Rae crustal rocks, were granites that are currently buried under Phanerozoic cover in the Buffalo Head-Chinchaga domains of northern Alberta. Unique U-Pb age peaks that would point to the Hearne craton as a sediment source were not identified. Hafnium model ages calculated from the upper Murmac Bay Group identify two periods of regional crustal growth at 2.83 Ga and 2.70 Ga, agreeing with Sm-Nd model ages from the western Churchill province.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".