Geochemical character of serpentinites associated with high‐ to ultrahigh‐pressure metamorphic rocks in the Alps, Cuba, and the Himalayas: Recycling of elements in subduction zones
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Bibliographic record
Abstract
Serpentinites associated with eclogitic rocks were examined from three areas: the Alps, Cuba, and the Himalayas. Most serpentinites have low Al/Si and high concentrations of Ir‐type platinum group elements (PGE) in bulk rock compositions, indicating that they are hydrated mantle peridotites. A few samples contain high Al/Si and low concentrations of Ir‐type PGE, suggesting that they are ultramafic cumulates. Among the hydrated mantle peridotites, we identified two groups, primarily on the basis of Al/Si and Mg/Si ratios: forearc mantle serpentinites and hydrated abyssal peridotites. Forearc serpentinites occur in the Himalayas and along a major deformation zone in Cuba. All serpentinites in the Alps and most serpentinites in Cuba are hydrated abyssal peridotites. Himalayan serpentinites have low Al/Si and high Mg/Si ratios in bulk rock compositions, and high Cr in spinel; they were serpentinized by fluids released from the subducted Indian continent and enriched in fluid‐mobile elements, and show high 87 Sr/ 86 Sr, up to 0.730, similar to the values of rocks of the subducted margin of the Indian continent. Although Himalayan serpentinites have a similar refractory geochemical signature as the Mariana forearc serpentinites, the former contain markedly high concentrations of fluid‐mobile elements and high 87 Sr/ 86 Sr compared to the latter that were hydrated by subducted Pacific Ocean crust. The data indicate that the enrichment of fluid‐mobile elements in forearc serpentinites depends on the composition of subducted slabs. Alpine serpentinites and most Cuban serpentinites show moderate Al/Si similar to abyssal peridotites. Hydration of peridotites near the seafloor is supported by micro‐Raman spectra of earlier formed lizardite, high δ 34 S (+11 to +17‰) of sulphides, and elevated 87 Sr/ 86 Sr, ranging from 0.7037 to 0.7095. The data support the contribution of S and Sr from seawater and sediments. These serpentinites are not highly enriched in fluid‐mobile elements because serpentinization occurred at a high water/rock ratio. Alkali elements are conspicuously unenriched in all serpentinites. This lack of alkali enrichment is explained by slab retention of alkalis. This is also consistent with the observation of relatively low alkali concentrations in volcanic front magmas, since partial melting related to the volcanic fronts is triggered by dehydration of serpentinites.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.000 | 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 it