Paleomagnetic consequence of thermal evolution of the North American Passive Margin: The Jurassic APWP controversy
Bibliographic record
Abstract
• New hypothesis for North American paleomagnetic Jurassic data discord. • Updated and refined Triassic-Jurassic APWP for the North American craton. • Reassessment of eastern vs. southwestern Jurassic paleomagnetic data. • Post-rifting thermal flexure deviated eastern group results on NA passive margin. • Three phases revealed for NA passive margin evolution during Jurassic. This study revisits the long-standing controversy in selecting Jurassic paleomagnetic data to define the North American (NA) craton APWP. Data from igneous rocks in the eastern part of NA and select global data rotated into NA coordinates define a high-latitude path. In contrast, the data from mostly sedimentary rocks in the NA Southwest interior (southwestern group) describe a lower-latitude path. Analysis suggests that previous explanations, such as inclination error in the southwestern group, cannot fully explain the disparity, and raises concerns that some magnetization of the eastern group may be partially secondary or younger, and others do not average secular variation. We present a new hypothesis that attributes the discrepancy to the post-tilt magnetization of the eastern NA continental margin caused by thermally induced non-uniform relative vertical movements during the post breakup evolution of northeast NA. This is tested by comparing mid-Jurassic paleomagnetic data of the eastern group with the coeval directions calculated from an updated late Triassic-Early Cretaceous reference NA APWP, presented here defined using a select and refined set of paleomagnetic poles mostly from southwestern region. One resolution is that a) after the breakup of NA from Africa (∼190 Ma), the thermally uplifted oceanside of the margin started to subside, while the more in-land regions experienced uplift due to landward lateral heat propagation in the lithosphere; b) during ∼190–140 Ma, the differential vertical motion tilted the edge of the margin eastward, about a horizontal axis with ∼53.5° azimuth. This eastward tilting peaked at ∼175–165 Ma and gradually decreased until ∼145–140 Ma. During this phase, the eastern group igneous rocks were emplaced and magnetized in this tilted framework; c) after ∼140–110 Ma, subsidence dominated the entire region. However, higher subsidence rates in more in-land parts tilted the marginal part along with their magnetizations acquired in the eastward-tilted position back (westward) to their current attitudes.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.003 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".