Early planetesimal accretion and magmatic records in achondrite meteorites
Bibliographic record
Abstract
Achondrite meteorites record the earliest evidence of volcanic activity in the Solar System.The 182 Hf-182 W records of noncarbonaceous (NC) iron meteorites provide model ages for core formation as early as 0.3 Myr after calcium-aluminium-rich inclusions (CAIs), supporting even earlier accretion times for their parent bodies [1].Stony achondrite meteorites provide evidence of early melting of chondritic [2] or differentiated [3] sources.These planetesimals were predominantly heated by the decay of short-lived radionuclide 26 Al (half-life ~0.7 Myr), which was subsequently enriched in crustal reservoirs during partial melting.Large uncertainties remain for modelling the accretion timescales owing to complex histories of magmatic differentiation and secondary processes (e.g., metamorphism, metasomatism, impact).The oldest known lava is an andesitic meteorite Erg Chech 002, which crystallized within ~2 Myr from CAIs [2, 4, 5].Using its chronological records, we model a best-fit planetesimal with a radius of 20-30 km that formed at ~0.1 Myr after CAIs [6].Angrites are sub-grouped either fine-grained volcanic angrites (formed 3-4 Myr after CAIs) or coarse-grained plutonic angrites (~10 Myr after CAIs).We obtained petrological and thermochronological records using U-Pb dating of mineral separates for an olivine-bearing plutonic angrite NWA 10463 [7] and of phosphates for NWA 10463 and the unique angritic dunite Northwest Africa (NWA) 8535.Phosphate SIMS U-Pb ages range from 4552±5 Myr to 4512±18 Myr (2s).In the absence of evidence of shock effects, such extended heating within the crust supports a relatively larger angrite parent body [8].
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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 | 0.001 |
| 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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".