Reconstructing the Paleoproterozoic Heart of Nuna, from Fennoscandia to Northeastern Laurentia
Bibliographic record
Abstract
Abstract Accurate palaeogeographical reconstructions of past supercontinents are necessary to test models of supercontinent cyclicity, secular variation in plate tectonics and mantle geodynamics. However, numerous factors limit our ability to reconstruct past supercontinents as is evident in the ongoing debates regarding the construction phase and geometry of Earth's most recent supercontinent, late Paleozoic to early Mesozoic Pangaea. An important factor in these debates, and a focus of our study is how best to palinspastically restore, in section and in plan-view, the orogenic belts along which supercontinents were stitched together. We utilize the orogenic belts spanning Baffin Island, Greenland and Fennoscandia that are inferred to record the assembly of the Paleoproterozoic supercontinent Columbia to test the accepted reconstruction of the Nuna core of Columbia. We show that as reconstructed in the Nuna model, each of Baffin Island, Greenland (with some complications) and Fennoscandia are characterized by an older cratonic backstop that gives way to younger accretionary complexes toward the inferred oceanic domain that lay to the south and which is inferred to have closed by subduction beneath northeastern Laurentia–Fennoscandia during Columbia assembly. This southward transition from cratonic backstop to accretionary orogen is a hallmark of upper plates in modern convergent plate margins and is consistent with the construction of the Columbia supercontinent, including its Nuna core, through plate tectonic processes, and provides a broad validation of the Nuna reconstruction and hence for Columbia as a whole. Map view curvature of the cratonic backstops is restricted to long wavelength, open bends consistent with the Archean crust having been characterized by significant lithospheric strength. The more accretionary southern portions of Nuna are, however, characterized by sinuous orogens that developed by oroclinal bending of formerly more linear belts, significantly complicating their palinspastic restoration and rendering detailed correlation of juvenile orogenic belts across Nuna problematic.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".