Lu-Hf age and Source of Mantle-Derived Rocks from the Saglek-Hebron Complex (Northern Labrador)
Bibliographic record
Abstract
Ancient mantle-derived rocks allow us to gain insights into the geochemical evolution of Earth's early mantle. We present a 176Lu-176Hf study of the Saglek-Hebron Complex (northern Labrador, Canada), which contains some of the oldest mafic and ultramafic rocks on the planet. Low-Fe ultramafic and basaltic metavolcanic rocks yield an isochron of 3934 ± 127 Ma with a suprachondritic initial epsHf=+8.9 ± 2.7. This value implies a highly incompatible-element depleted source for these rocks, which was more depleted than the Depleted Mantle estimates at the same age. Decoupled Sm-Nd and Lu-Hf systematics can be explained by ancient source depletion during a magma ocean in the garnet stability field. High-Fe ultramafic rocks yield an isochron corresponding to an age of 3405 ± 503 Ma. Mafic intrusions were age-dated at 3875 ± 454 Ma and at 2716 ± 370 Ma. The Saglek-Hebron Complex has recorded mantle-derived magmatism for over 1 billion years.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".