The oceanic crustal structure at the extinct, slow to ultraslow Labrador Sea spreading center
Bibliographic record
Abstract
Abstract Two seismic refraction lines were acquired along and across the extinct Labrador Sea spreading center during the Seismic Investigations off Greenland, Newfoundland and Labrador 2009 cruise. We derived two P wave velocity models using both forward modeling (RAYINVR) and traveltime tomography inversion (Tomo2D) with good ray coverage down to the mantle. Slow‐spreading Paleocene oceanic crust has a thickness of 5 km, while the Eocene crust created by ultraslow spreading is as thin as 3.5 km. The upper crustal velocity is affected by fracturation due to a dominant tectonic extension during the waning stage of spreading, with a velocity drop of 0.5 to 1 km/s when compared to Paleocene upper crustal velocities (5.2–6.0 km/s). The overall crustal structure is similar to active ultraslow‐spreading centers like the Mohns Ridge or the South West Indian Ridge with lower crustal velocities of 6.0–7.0 km/s. An oceanic core complex is imaged on a 50 km long segment of the ridge perpendicular line with serpentinized peridotites (7.3–7.9 km/s) found 1.5 km below the basement. The second, ridge‐parallel line also shows extremely thin crust in the extinct axial valley, where 8 km/s mantle velocity is imaged just 1.5 km below the basement. This thin crust is interpreted as crust formed by ultraslow spreading, which was thinned by tectonic extension.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".