Imbrium Age for Zircons in Apollo 17 South Massif Impact Melt Breccia 73155
Bibliographic record
Abstract
Abstract The Apollo 17 poikilitic impact melt breccias were initially interpreted to be directly related to the Serenitatis basin formation. Here we present petrological, geochemical, and U‐Pb geochronological investigations of the poikilitic impact melt of Apollo 73155,69 which was sampled from the South Massif of the Taurus‐Littrow valley. Nanoscale secondary ion mass spectrometry analyses of well‐preserved poikilitic zircons from sample 73155,69 yield a uniform 207Pb/206Pb age population with a weighted mean age of 3921 ± 14 Ma. The zircons have distinctly high concentrations of Y (3279−6347 ppm) and Th (254−302 ppm) compared with other Apollo 17 zircons. These characteristics, together with their textures, are remarkably similar to those of zircons from high‐Th melt breccias from Apollo 12 samples and lunar meteorite Sayh al Uhaymir 169 attributed to the formation of the high‐Th deposits of the Imbrium basin. We therefore propose an Imbrium provenance for melt component in 73155,69. Our results provide new evidence for components of Imbrium‐type ejecta occurring among the South Massif breccias. Consequently, the Apollo 17 poikilitic impact melt breccias may not represent Serenitatis ejecta.
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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 | 0.000 | 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) | 0.002 | 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".