Preservation of primordial signatures of water in highly-shocked ancient lunar rocks
Bibliographic record
Abstract
Spurred by the discovery of water in lunar volcanic glasses about a decade ago, the accessory mineral apatite became the primary target to investigate the abundance and source of lunar water. This is due to its ability to contain significant amounts of OH in its structure, along with the widespread presence of apatite in lunar rocks. There is a general understanding that crustal cumulate rocks of the lunar magnesian (Mg) suite are better candidates for recording the original isotopic compositions of volatile elements in their parental melts compared to eruptive rocks, such as mare basalts. Consequently, water-bearing minerals in Mg-suite rocks are thought to be ideal candidates for discerning the primary hydrogen isotopic composition of water in the lunar interior. Mg-suite rocks and most other Apollo samples that were collected at the lunar surface display variable degrees of shock-deformation. In this study, we have investigated seven Apollo 17 Mg-suite samples that include troctolite, gabbro and norite lithologies, in order to understand if shock processes affected the water abundances and/or H isotopic composition of apatite. The measured water contents in apatite grains range from 31 to 964 ppm, with associated δD values varying between −535 ± 134‰ and +147 ± 194‰ (2σ). Considering the full dataset, there appears to be no correlation between H2O and δD of apatite and the level of shock each apatite grain has experienced. However, the lowest δD was recorded by individual, water-poor (<∼100 ppm H2O) apatite grains that are either directly in contact with an impact melt or in its proximity. Therefore, the low-δD signature of apatite could be a result of interactions with D-poor regolith (solar wind derived H), facilitated by shock-induced nanostructures that could have provided pathways for migration of volatiles. In contrast, in relatively water-rich apatites (>∼100 ppm H2O), regardless of the complexity of the shock-induced nanostructures, there appears to be no evidence of water-loss or alteration in their δD. The weighted average δD value of 24 such water-rich apatites is −192 ± 71‰, and, of all 36 analyzed spots is −209 ± 47‰, indistinguishable from that of other KREEPy lunar lithologies or the Earth's deep mantle. Despite experiencing variable degrees of shock-deformation at a later stage in lunar history, water-rich apatite in some of the earliest-formed lunar crustal material appears to retain the original isotopic signature of H in the Moon.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".