Congo-São Francisco craton in Paleoproterozoic-Mesoproterozoic supercontinent Nuna
Bibliographic record
Abstract
The location of the Congo-São Francisco (CSF) craton, one of the largest cratons in Proterozoic paleogeography, has been poorly constrained for the supercontinent Nuna interval (ca. 1800–1300 Ma). Initial models of Nuna suggested that the CSF craton was part of the Atlantica continent, together with Amazonia, West Africa, and perhaps Río de la Plata, as a separate continental block from other Nuna constituents. In other Nuna models the CSF craton has been placed adjacent to Baltica and Siberia, the core of Nuna, based mainly on ages of mafic magmatism and sparse paleomagnetic data. Through a geochemical, geochronological and paleomagnetic study of the WNW-trending Virei mafic dykes, which extend outward from the Mesoproterozoic Kunene Igneous Complex in southwest Angola, we provide a U-Pb baddeleyite age of 1385 ± 5 Ma, geochemical signatures, and a robust Mesoproterozoic paleomagnetic pole to test the CSF craton’s placement within Nuna. Including our new pole with quality-filtered poles from the other cratons during the Nuna interval, we propose a refined Nuna model with (1) southwest Congo / west Siberia cratonic connection at 1700–1500 Ma, (2) proximity of Amazonia and West Africa cratons, and (3) connection of southwest Congo craton with northwest West Africa at 1380 Ma. Our proposed 1500–1380 Ma reconstructions are further supported by matching large igneous province (LIP) records from these crustal blocks. The new 1385 Ma Virei pole, when considered relative to an earlier CSF pole at ca. 1500 Ma, requires substantial azimuthal rotation (∼85°) of CSF in the intervening time interval. To accommodate both the matching LIP records and paleomagnetic data from CSF and neighboring cratons in Nuna, we propose an interval of transform motion near the supercontinent’s periphery prior to more widespread mid-Mesoproterozoic supercontinental breakup.
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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 | 0.001 |
| 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) | 0.002 | 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".