A failed search for concordancy across multiple isotopic systems in lunar impactites: Implications for testing the Late Heavy Bombardment hypothesis

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dc.citation.articleNumber118943en_US
dc.citation.journalTitleEarth and Planetary Science Lettersen_US
dc.citation.volumeNumber646en_US
dc.contributor.authorHarrison, T. Marken_US
dc.contributor.authorZhang, Bidongen_US
dc.contributor.authorParisi, Andrew F.en_US
dc.contributor.authorBell, Elizabeth A.en_US
dc.date.accessioned2024-10-08T13:28:37Zen_US
dc.date.available2024-10-08T13:28:37Zen_US
dc.date.issued2024en_US
dc.description.abstractInvestigations of Apollo-returned samples radically altered our understanding of lunar history which has important implications for terrestrial habitability and Solar System evolution. Radiometric dating of those samples inspired the hypothesis that Moon experienced a Late Heavy Bombardment (LHB) at ∼3.9 Ga. The LHB concept has come under several recent challenges, including the concern that 40Ar/39Ar step-heating dates of Apollo impactites had been misinterpreted. Ultraviolet laser ablation (UVLAMP) 40Ar/39Ar dates – with their capacity for much higher spatial resolution and thus potential to avoid dating near-ubiquitous clasts in impact melt rocks – should in principle provide more interpretable results. Here we compare new ion microprobe 207Pb/206Pb accessory mineral dates for two Apollo 17 impactites for which UVLAMP 40Ar/39Ar dates had been previously obtained. Our results are consistent with a single accessory phase growth event for each sample, though the two samples yielded statistically different mean ages of ca. 3.974±0.013 and 3.928±0.003 Ga. Both can reasonably be interpreted as dating an impact event, but the 207Pb/206Pb dates are older than the associated 40Ar/39Ar dates by several hundred million years. We interpret that the age differences result from subsequent thermal disturbances. The discordancy between impact ages inferred from lunar impactites using two different radiometric systems suggests caution in acceptance of the LHB hypothesis without the benefit of both larger lunar datasets and more multichronometric studies. Even with such information, our capacity to know the lunar bombardment history is likely limited by compositional and thermal effects which appear to restrict growth of impact-produced accessory minerals to a small fraction of the lunar surface. Using currently available datasets, the LHB hypothesis may be effectively untestable.en_US
dc.identifier.citationHarrison, T. M., Zhang, B., Parisi, A. F., & Bell, E. A. (2024). A failed search for concordancy across multiple isotopic systems in lunar impactites: Implications for testing the Late Heavy Bombardment hypothesis. Earth and Planetary Science Letters, 646, 118943. https://doi.org/10.1016/j.epsl.2024.118943en_US
dc.identifier.digital1-s2-0-S0012821X24003765-mainen_US
dc.identifier.doihttps://doi.org/10.1016/j.epsl.2024.118943en_US
dc.identifier.urihttps://hdl.handle.net/1911/117931en_US
dc.language.isoengen_US
dc.publisherElsevieren_US
dc.rightsExcept where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial (CC BY-NC) license. Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.rights.urihttps://creativecommons.org/licenses/by-nc/4.0/en_US
dc.titleA failed search for concordancy across multiple isotopic systems in lunar impactites: Implications for testing the Late Heavy Bombardment hypothesisen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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