Detrital zircon geochronology of the Paleoproterozoic Nonacho Basin (Northwest Territories, Canada): A record of post-collisional collapse amid supercontinent aggregation
Bibliographic record
Abstract
• New maximum depositional age for the Nonacho Group of 1887 ± 10 Ma. • Erosional record of Taltson and Thelon orogens preserved in the Nonacho Basin. • Correlations with other Rae craton Paleoproterozoic supracrustal rocks. • Model of basin evolution in response to craton amalgamation. The study of Paleoproterozoic sedimentary basins is critical to inform aspects of craton development during some of Earth’s earliest supercontinent cycles. The ∼ 1.9 Ga Nonacho Basin is located at the ancestral core of the Canadian Shield near the sutured margins of the Archean Slave and Rae cratons, making it ideal for a detrital zircon study examining evidence of orogenic unroofing during the ca. 1.9 Ga assembly of the supercontinent Nuna. Detrital zircon U–Pb geochronology with chemical-abrasion laser-ablation inductively-coupled plasma mass spectrometry is used to investigate the provenance and maximum depositional ages of the Nonacho Group throughout its alluvial, fluvial and marine deposition. Detritus preserved in the lower stratigraphy (Hjalmar formation) was largely derived locally from the ∼ 2.7–2.3 Ga Nonacho basement complex. The overlying strata (Tronka Chua, Chief Nataway, Newshethdezza, Thekulthili, and Taltson formations) display distinctive age peaks matching the ∼ 2.0–1.9 Ga Thelon and Taltson orogens, together with contributions from varied source areas of the Rae craton. A maximum depositional age at 1887 ± 10 Ma for the Tronka Chua formation indicates that much of the sediment was deposited post ∼ 1.89 Ga, similarly to correlative supracrustal panels of the central Rae craton. This new depositional constraint, together with records of Taltson- and Thelon-derived detritus, corroborate a model whereby the Nonacho Basin evolved in a regime of crustal extension driven by thermal subsidence in the aftermath of the Slave and Rae craton collision, punctuated by crustal flexure as a distant response to the Snowbird orogeny. The Nonacho Group acted as a sink for sediment unroofed from nearby orogenic topography until crustal flexure originating from the Rae-Hearne craton boundary triggered alternate sources, providing an example of how multistage convergence during supercontinent amalgamation controls sediment provenance.
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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 | 0.002 |
| 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) | 0.003 | 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".