Discovery of ancient and active hydrothermal systems along the ultra‐slow spreading Southwest Indian Ridge 10°–16°E
Bibliographic record
Abstract
We report the discovery of active and fossil hydrothermal systems during R/V Knorr Cruise 162, Legs VII and IX along a 400 km long segment of the ultra‐slow Southwest Indian Ridge (SWIR) between 10 and 16°E, where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date (8.4 mm yr−1 full rate). Eight of forty‐one optical/temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others. Fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias, four deposits ofsepiolite and silica, as well as Mn‐oxide and nontronite cemented breccias. The massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep‐seated normal fault bounding the southern rift valley wall. Silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low‐ to moderate‐temperature ultramafic‐hosted hydrothermal activity. The abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates, and hence the magmatic heat input, along this section of the SWIR are lower than on any other explored segment of the global mid‐ocean ridge system. This observation suggests that high mantle upwelling and magma supply rates are not required to drive mid‐ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra‐slow end of the ridge spreading spectrum. The frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation, with hydrothermal vent sites being preferentially associated with long‐lived faults that provide fluid pathways. Our results suggest the contribution of magma‐starved ridge segments to the global ocean‐lithosphere geochemical budget is potentially much larger than previously thought.
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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 | 0.000 | 0.000 |
| 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".