Impact history of the Apollo 17 landing site revealed by U-Pb SIMS ages
MetadataShow full item record
Secondary ion mass spectrometry (SIMS) U-Pb ages of Ca-phosphates from four texturally distinct breccia samples (72255, 76055, 76015, 76215) collected at the Apollo 17 landing site were obtained in an attempt to identify whether they represent a single or several impact event(s). The determined ages, combined with inferences from petrologic relationships, may indicate two or possibly three different impact events at 3920 ± 3 Ma, 3922 ± 5 Ma, and 3930 ± 5 Ma (all errors 2s). Searching for possible sources of the breccias by calculating the continuous ejecta radii of impact basins and large craters as well as their expected ejecta thicknesses, we conclude that Nectaris, Crisium, Serenitatis, and Imbrium are likely candidates. If the previous interpretation that the micropoikilitic breccias collected at the North Massif represent Serenitatis ejecta is correct, then the average 207Pb/206Pb age of 3930 ± 5 Ma (2s) dates the formation of the Serenitatis basin. The occurrence of zircon in the breccias sampled at the South Massif, which contain Ca-phosphates yielding an age of 3922 ± 5 Ma (2s), may indicate that the breccia originated from within the Procellarum KREEP terrane (PKT) and the Imbrium basin appears to be the only basin that could have sourced them. However, this interpretation implies that all basins suggested to fall stratigraphically between Serenitatis and Imbrium formed within a short (<11 Ma) time interval, highlighting serious contradictions between global stratigraphic constraints, sample interpretation, and chronological data. Alternatively, the slightly older age of the two micropoikilitic breccias may be a result of incomplete resetting of the U-Pb system preserved in some phosphate grains. Based on the currently available data set this possibility cannot be excluded.
Showing items related by title, author, creator and subject.
Complex magmatic and impact history prior to 4.1 Ga recorded in zircon from Apollo 17 South Massif aphanitic breccia 73235Grange, Marion; Nemchin, Alexander; Timms, Nicholas Eric; Pidgeon, Robert; Meyer, C. (2011)Sample 73235 is one of several aphanitic impact melt breccias collected by the Apollo 17 mission at stations 2 and 3 on the slopes of the South Massif. This study presents a detailed investigation of internal structures ...
Phosphate ages in Apollo 14 breccias: Resolving multiple impact events with high precision U-Pb SIMS analysesSnape, J.; Nemchin, Alexander; Grange, Marion; Bellucci, J.; Thiessen, F.; Whitehouse, M. (2016)© 2015 Elsevier Ltd. The U-Pb systems of apatite and merrillite grains within four separate Apollo 14 impact melt breccia samples were analysed by secondary ion mass spectrometry. No systematic difference was identified ...
Grange, Marion; Nemchin, Alexander; Pidgeon, Robert; Timms, Nicholas Eric; Muhling, J.; Kennedy, Allen (2009)Lunar breccia 73217 is composed of plagioclase and pyroxene clasts originating from a single gabbronorite intrusion, mixed with a silica-rich glass interpreted to represent an impact melt. A study of accessory minerals ...