Detrital Zircon Geochronology with Applications to North American Tectonics
Bibliographic record
Abstract
Detrital zircons from rocks in the eastern and western portions of the North American Cordillera were used to constrain tectonic models for the orogen. In the eastern Cordillera, regional provenance patterns in latest-Neoproterozoic to Cambrian sandstones were analysed and five detrital zircon facies defined based on statistical intercomparison using multi-dimensional scaling. Detrital zircon facies occur in unique geographical regions reflecting proximity to the major tectonic provinces of Laurentia. Samples from northern regions are dominated by Archean and Paleoproterozoic zircons derived from Archean cratons and orogenic belts that record their assembly. More southerly sample locations show an increase in detrital zircons derived from younger Paleoproterozoic orogenic belts and early Mesoproterozoic intrusive suites. Detrital zircons from Grenville–aged sources are common in the south. The east-west continuity of detrital zircon facies between rocks of the North American and Cassiar/Antler platforms argues against the latter being exotic with respect to North America, supports the back-arc models for Cordilleran orogenesis, and argues against models involving Jurassic or Cretaceous ribbon continent collision. In the western Cordillera we compare detrital zircon populations from the Nanaimo Basin, Vancouver Island, British Columbia, to potential source areas in western North America to test hypothesized northern and southern Cretaceous paleogeographic positions for the basin. Our detrital zircon data suggest that sediment in the Nanaimo Basin derives from the Western Coast Mountains Batholith and the Mojave-Sonoran Region of southwestern North America, supporting a southerly Cretaceous paleogeographic position and confirming previous paleomagnetic estimates. A speculative Cretaceous to Paleogene paleogeographic reconstruction for the southwestern United States and northern Mexico that accommodates the presence, and northward transport, of the westernmost terrane of the Cordillera is presented. It is proposed that the Western Coast Mountains Batholith and the Nanaimo Basin represent the missing segment of the Mesozoic magmatic arc and associated forearc regions, between the Sierra Nevada and Peninsular Ranges Batholiths. This segment was translated northward following capture by the Kula plate. As such, we reconcile the paleomagnetic data for the Baja-BC block with the geology of the southwestern United States. Our model, albeit speculative, is compatible with the large-scale tectonic and magmatic processes that affected western North America in the Late Cretaceous and Paleogene.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".