U–Pb baddeleyite crystallization age for a Corson diabase intrusion: possible Midcontinent Rift magmatism in eastern South Dakota
Bibliographic record
Abstract
The largely buried basement of the northern Great Plains includes suture zones and terrane boundaries that represent a significant part of the growth of Laurentia in the Proterozoic. Basement exposures in this region east of the Black Hills are rare. In southeastern South Dakota, southwestern Minnesota, northeastern Nebraska, and northwestern Iowa, small outcrops of the Proterozoic Sioux Quartzite occur. In southeastern South Dakota, Corson diabase sills or dykes have intruded the quartzite. U–Pb ID–TIMS baddeleyite data from a Corson diabase sample yield an upper intercept date of 1149.4 ± 7.3 Ma, suggesting the diabase is related temporally to the Midcontinent Rift (MCR). The similarity in age of this diabase to the Inspiration sill, Pigeon River, Kipling, and Abitibi dykes suggests that early Midcontinent Rift development was not localized within the Nipigon Embayment, but extended along a roughly east–northeast zone from the Abitibi dykes to the Corson diabase. The presence of the Corson intrusions 250 km west of the MCR is hypothesized to represent a failed rift arm within the Superior craton. The greater strength of the Superior craton relative to lithosphere south of the Spirit Lake tectonic zone resulted in a shift of the southwestern rift arm in southern Minnesota along the Belle Plaine fault southeastward to the Iowa border. Alternatively, the apparent northeast trend of known occurrences of the Corson diabase is also consistent with a mantle plume centre explanation for early Midcontinent rifting.
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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) | 0.002 | 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".