Whole-rock Fe isotope compositions as mantle source and process tracers across the Hawaiian archipelago
Bibliographic record
Abstract
We present a geographically extensive Hawaiian Fe isotope dataset, with the primary goal of testing the use of stable Fe isotopes to identify mantle heterogeneities in the source of Hawaiian volcanoes, including whether the isotopically distinct Hawaiian geochemical groups (Loa, Kea, and Enriched Loa) exhibit distinct Fe isotope compositions. Hawai‘i is an excellent natural laboratory for assessing newer isotopic systems as it is well-studied and thoroughly geochemically characterized. We analyzed 43 carefully selected shield-stage tholeiitic basalt samples from 14 subaerial and submarine volcanoes that represent the past ∼ 5 Ma of volcanic activity along the Hawaiian chain. These samples have previously been thoroughly characterized for their major and trace element concentrations, and Pb, Sr, Nd, Hf, and Tl isotope compositions. Their compositions span the entire range of Kea, Loa and Enriched Loa Hawaiian geochemical groups. Iron isotope results reported to IRMM-14 vary from a δ 56 Fe (±2SD) of 0.00 (±0.06 ‰) to 0.21 (±0.02 ‰). The data adjusted for olivine fractionation show a similar range, and the mean δ 56 Fe of the new data (0.10 ± 0.10 ‰) overlaps with the average MORB value (∼0.10 ‰). This work provides the first comprehensive, large-scale overview of Fe isotope compositions in shield-stage tholeiitic basalt across the Hawaiian archipelago. Important observations include: 1) there is no statistical difference in δ 56 Fe values between Loa, Kea, and Enriched Loa geochemical groups; 2) δ 56 Fe and lithophile radiogenic isotope ratios (Pb, Sr, Nd, Hf) show no correlations; and 3) δ 56 Fe and ε 205 Tl (used to track the presence of recycled pelagic sediments in Hawaiian basalts) are not correlated. Hawaiian δ 56 Fe values are slightly lower than those from other enriched oceanic islands (EM-I, EM-II, HIMU), including Pitcairn, Azores, and Samoa, which is a feature also observed in Iceland. On a broader scale, these observations suggest that the mantle heterogeneities contributing to the unique radiogenic isotopic signatures in Hawaiian lavas, which are interpreted as being linked to the Pacific Large Low Shear Velocity Province, do not exhibit distinct or heavy Fe isotope compositions. Alternatively, if the deep mantle reservoirs sampled by the Hawaiian plume have distinct Fe isotope compositions, these signatures are not preserved during the ascent through the mantle, melting, and eruption at the surface.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".