Boron isotopes trace an increase in subduction-driven recycling of fluid-mobile elements in the Neoarchean
Bibliographic record
Abstract
The deep recycling of surface material into Earth’s mantle is an integral process governing global water and fluid-mobile element cycles. This recycling is largely predicated on subduction operating efficiently, which may not apply for the first two billion years of Earth’s history. Tracing the initiation and evolution of the modern deep fluid-mobile element cycle requires determining when the mantle first became modified by subducted surface-derived materials on a global scale. The B isotope system provides a unique geochemical parameter to test for early signatures of such recycling, given that B is enriched and isotopically fractionated at Earth’s surface, depleted in the mantle, and mobilized by fluids and fluid-rock interaction. In this study, B isotopes of granitoids from seven Archean cratons are analyzed to trace the early signatures of recycling of surface-altered materials. When filtered for alteration and (post-)magmatic B modification, the B isotope compositions of the sample set show substantial variation. The range exhibited by sanukitoids (−8.9 ‰ to −1.6 ‰, mean: −4.7 ‰, n = 5) overlaps with other granitoids (−15.8 ‰ to +8.0 ‰, mean: −8.6 ‰, n = 30), but the average B isotope composition of sanukitoids is higher than other granitoids. The granitoids reveal a temporal diversification towards, on average, higher 11 B/ 10 B values from the Neoarchean onward. The heavier B isotope values reflect the recycling of surface-derived B into the melt source along a geotherm that was cold enough to prevent total loss of B through dehydration reactions, consistent with a cold-subduction geotherm. The B data thus indicate that the subduction-driven recycling of surface-derived materials into the mantle became more prevalent since the Neoarchean, marking this era as the likely starting point for the modern deep fluid-mobile element and water cycle.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 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".