Devonian Extension in Northwestern Newfoundland: <sup>40</sup>Ar/<sup>39</sup>Ar and U‐Pb Data from the Ming’s Bight Area, Baie Verte Peninsula
Bibliographic record
Abstract
The Ming’s Bight Group of northwestern Newfoundland, an outlier of Humber Zone continental margin rocks, is entirely surrounded by ophiolitic rocks of the Dunnage Zone. Structures in the Ming’s Bight Group and adjacent units record three main phases of deformation. The earliest structures relate to Silurian sinistral transpression previously documented in the region. Two later phases of extensional deformation produced a series of dextral oblique‐normal shear zones and faults that now separate the Ming’s Bight Group in the footwall from ophiolitic and granitoid rocks in the hangingwall. 40Ar/39Ar and U‐Pb data constrain the times of oblique‐normal shear and cooling. Metagabbro in the Point Rousse Ophiolite Complex, which lies in the hangingwall, preserves disturbed Ordovician hornblende 40Ar/39Ar ages, whereas adjacent shear zones record Devonian ages. Hornblendes in Pacquet Harbour Group amphibolites within extensional shear zones mainly record 40Ar/39Ar ages of 390–380 Ma. Synkinematic titanite and rutile porphyroblasts from an extensional shear zone on the northwestern margin of the Ming’s Bight Group have been dated by the U‐Pb method at 388 and 380 Ma, interpreted as growth and cooling ages, respectively. The titanite and hornblende ages suggest that the main phase of ductile oblique‐normal shear was underway at 405–385 Ma. Ming’s Bight Group schists and pegmatites produced concordant muscovite 40Ar/39Ar ages averaging 362 Ma, interpreted as the time of footwall cooling below 350°C. We suggest that the Ming’s Bight Group is a mid‐Devonian symmetrical core complex formed within a local transtensional regime developed during dextral oblique transcurrent movement along the Baie Verte Line. The timing and tectonic setting of extension do not support recent models for “extensional collapse” in the northern Appalachians.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 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 teacher head, 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".