A Rare Glimpse of Paleoproterozoic Sub‐Arc Mantle: The Ussuit Peridotite, West Greenland
Bibliographic record
Abstract
Abstract Mantle residues beneath Archean cratonic nuclei have been extensively studied, whereas less attention has been given to the mantle lithosphere beneath Proterozoic mobile belts that link these nuclei. Rare mantle tectonites within tectonic mélanges of Paleoproterozoic mobile belts provide information important to understanding the broader processes involved in the construction of the cratonic mantle lithosphere. Here we present mineral compositions, bulk‐rock major, trace, and platinum group elements, Re‐Os isotopes, and olivine oxygen isotopes from a Paleoproterozoic mantle tectonite in West Greenland–the Ussuit peridotite. The Ussuit peridotite was emplaced in the crust during the Nagssugtoqidian orogeny between 1,870 Ma and 1,775 Ma and preserves primary melt depleted characteristics that reflect >30% melting, for example, Al2O3 < 0.4 wt.%, Ti < 10 ppm, Lu/Yb > 0.25, and Mg #s up to 93. Cryptic signatures of hydrous melting, for example, spinel Cr #’s >65, Os/Ir ratios between 0.3 and 6, and supramantle olivine δ18O values, suggest that the high degree of melt depletion was partly inherited from a forearc or sub‐arc melting environment. Re‐Os isotopic systematics show melt depletion occurred at ∼2 Ga overlapping the juvenile oceanic arc crust that hosts the peridotites. This age coincides with a peak in the global production of juvenile cratonic lithosphere. Furthermore, the global Paleoproterozoic cratonic mantle has strong geochemical similarities with the Ussuit peridotites. It is suggested that subduction zone peridotites form key components of the Paleoproterozoic cratonic lithospheric mantle, creating a viscous, buoyant mantle lithosphere that contributed to the long‐term stability of the greater cratonic masses.
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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 | 0.000 | 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".