Detrital zircons from Cambrian rocks of western Laurentia define two episodes of Rodinian rift-related magmatism
Bibliographic record
Abstract
Many aspects of the disassembly of Neoproterozoic supercontinent Rodinia remain poorly constrained. Current models for the breakup along western Laurentia (present coordinates) do not fully reconcile stratigraphic observations regarding the timing and mechanisms of continental rifting. Latest Neoproterozoic to Cambrian stratigraphic units exposed along the North American Cordillera from southwestern Canada to the southwestern United States contain Neoproterozoic and Cambrian zircons interpreted to be sourced from rift-related igneous rocks generated during the fragmentation of Rodinia. Two discrete magmatic episodes distinguished by a ca. 50 Myr period of apparent magmatic quiescence are identified using the detrital record: (1) Tonian and Cryogenian to earliest Ediacaran magmatism (mantle plume events followed by rifting); and (2) latest Ediacaran to late Cambrian magmatism. The detrital zircon record of the first episode supports a 660–650 Ma rift-to-drift transition followed by passive margin sedimentation of the upper Windermere Supergroup. After a period of apparent magmatic quiescence from 630–580 Ma, detrital zircon dates of 580–520 Ma from central-western Laurentia provide evidence for renewed rift magmatism preceding the initiation of the lower Paleozoic passive margin. These new U-Pb dates are used to present a refined model of Rodinia disassembly with improved timing constraints suggesting that its final breakup and the Sauk I transgression occurred ca. 520 Ma, in accordance with recent revisions to the timing of the Sauk transgressions in southwestern Laurentia.
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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 | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".