Fluid flow patterns in fast spreading East Pacific Rise crust exposed at Hess Deep
Bibliographic record
Abstract
Tectonic exposures of a volcanic sequence and sheeted dike complex over a 4‐km‐wide region at Hess Deep (equatorial Pacific) reveal significant spatial heterogeneity (10–103 m) in the extent and nature of hydrothermal alteration in young, fast spreading East Pacific Rise crust. The volcanic sequence is fairly uniformly altered, with only minor oxidation and alteration to clay minerals. Sheeted dikes in the eastern part of the field area are highly fractured with narrow intervals of intact dikes that dip up to 60°. Their alteration characteristics show a simple depth trend such that with increasing depth the dominant secondary mafic mineral changes from chlorite to amphibole, clinopyroxene replacement increases (<20% to >40%), whole rock δ18O values decreases (4.4–5.5‰ to 3.5–4.5‰), and calculated peak metamorphic temperatures increase (∼250°C to 450°–700°C). Within the deepest dikes, localized zones up to 400‐m‐wide are chlorite‐rich and have low‐δ18O (2.9–4.1‰) and low peak metamorphic temperatures (∼345°C). These alteration patterns likely formed within broad recharge zones whereby the low‐δ18O zones developed in the regions with the highest fluid flux. In the west, massive, slightly rotated sheeted dikes near the volcanic‐sheeted dike transition are δ18O and Cu depleted and display higher peak temperatures (≥345°C) than elsewhere in the shallow dikes. These characteristics are consistent with formation within a high temperature, hydrothermal discharge zone. We propose that the spreading history of a fast spreading ridge segment can create significant spatial heterogeneity in fluid flow and alteration patterns within sheeted dike complexes, similar to those preserved in many ophiolites.
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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".