Texturally controlled oxygen isotope analyses of serpentine phases record the multistage hydration history during abyssal serpentinization
Bibliographic record
Abstract
Serpentinization of ultramafic mantle rocks is one of the main reactions leading to a significant water incorporation into the oceanic lithosphere. The multiphase hydration is yet poorly constrained, in terms of sequence of events, their chemical and isotopic compositions, and the reaction conditions (temperature, fluid composition and the water/rock ratio). We present here the first study on Iberia and Newfoundland passive margins samples (oceanic drill core samples, ODP, from Site 1070 and Site 1277) that closely correlates petrographic observation, in situ oxygen isotopic data and major and trace elements mobility in serpentine phase. The serpentine minerals lizardite and chrysotile are the main hydrous phases formed during the serpentinization reaction. These minerals crystallize in specific textures, depending on the primary minerals being replaced: (i) serpentine in mesh texture after the alteration of olivine, and (ii) serpentine as bastite pseudomorphing pyroxenes. As the textural control is the key to detect multistage fluid uptake during progressive hydration, we used Secondary Ion Mass Spectrometry (SIMS) to achieve a good spatial resolution of ∼20 µm for in situ oxygen isotope measurements. The trace elements analyses were analyzed with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and a spot size of ∼38 µm. Newfoundland samples show less variability in the oxygen isotope composition than Iberia samples and have values higher than the mantle composition, suggesting low temperature of serpentinization (110-200°C). One of the Iberia samples shows similar variability of the oxygen isotope composition but lower values than 𝛿18Omantle (temperature around 140-200°C). The second sample has the highest variability: (i) homogeneous mesh rim texture with 𝛿18O = 4.4 ± 0.8 ‰ (2𝜎), (ii) wide compositional range for mesh centers with 𝛿18O = 4.0 - 7.7 ‰, and (iii) bastite with large isotopic variation from 5.5 to 13.5 ‰. These values suggest a large hydration temperature range from 60-200°C within a single sample. Texturally controlled rare-earth element (REE) analyses of the serpentine minerals reveal inherited, typical melt depletion patterns of the protolith, for both localities. The trace element composition of serpentine in the different textural domains displays typical signatures related to the precursor minerals (olivine vs. pyroxene), particularly in terms of Ni/Cr ratio. Positive anomalies of fluid-mobile elements (e.g. B, Sr, As) confirm hydration of the mantle rocks during oceanic serpentinization.
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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 | 0.000 |
| 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".