THE EAST PACIFIC RISE CRUSTAL THICKNESS, MOHO TRANSITION ZONE CHARACTER AND OFF-AXIS MAGMA LENS MELT CONTENT FROM 9°37.5âN TO 9°57âN: RESULTS FROM THREE-DIMENSIONAL MULTICHANNEL SEISMIC DATA ANALYSIS
Bibliographic record
Abstract
This thesis discusses the results from the first multi-source and multi-streamer three-dimensional multichannel seismic experiment conducted over a mid-ocean ridge environment. Prestack time migration was applied to the dataset resulting in the most detailed reflection images of a spreading center and its flanks to date. The key products from this work are maps of crustal velocities, crustal thickness, and Moho transition zone (MTZ) reflection character for a section of the fast-spreading East Pacific Rise (EPR) from 9°37.5’N to 9°57’N, excluding the area from 9°40’N to 9°42’N where no data were collected. Moho reflections were imaged within ~92% of the study area. The derived average crustal thickness and average crustal velocity for the investigated ~880 km2 area are 5920±320 m and 6320±290 m/s, respectively. The average crustal thickness varies little from Pacific to Cocos plate suggesting mostly uniform crustal production in the last ~180 Ka.\nDetailed analysis of the crustal thickness and MTZ reflection character shows that the third-order segmentation is governed by melt extraction processes within the uppermost mantle while the fourth-order ridge segmentation arises from mid- to upper-crustal processes. This analysis also suggests that both the mechanism of lower-crustal accretion and the volume of melt delivered to the crust vary along the investigated section of the EPR. More efficient mantle melt extraction is inferred at latitudes from 9°42’N to 9°51.5’N, with greater proportion of the lower crust accreted from the AML than for the rest of the study area. Larger volume of melt is delivered to the crust from 9°37.5’N to 9°40’N than to the investigated crust further north. At some locations, the Moho reflections are for the first time unambiguously imaged below the AML away from any ridge discontinuity suggesting that the Moho is formed at zero age at least at some sections of the spreading centers. The first study of the melt content of mid-crustal off-axis magma lenses (OAML), done using amplitude variation with offset technique calibrated for a magmatic plumbing system, shows that these magma bodies contain 0 to 20% melt. This suggests that OAMLs likely contribute little to the overall crustal formation.
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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 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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) | 0.001 | 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".