An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples

Abstract

Abstract-Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1-2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine-grained (grain size <0.3 mm), a "paired samples t-test" can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.

Complex burial histories of Apollo 12 basaltic soil grains derived from cosmogenic noble gases: Implications for local regolith evolution and future in situ investigations

“…(2014, 2018) and Alexander et al. (2014, 2016). Olivine, pigeonite, and ilmenite type basalts are based on the scheme of Neal and Taylor (1992) and Neal et al.…”

“…One aliquot of each mechanically broken particle was used for petrology and bulk chemistry analysis, the methods and findings of which are reported by Alexander (2015), Alexander et al. (2016), and Snape et al. (2014).…”

“…This work uses the bulk chemistries determined by Alexander (2015), Alexander et al. (2016), and Snape et al. (2014) in order to determine the sample‐specific concentrations of target elements for spallation‐derived noble gas species (of He, Ne, and Ar).…”

“… b Defined originally as feldspathic (Snape et al., 2014), but later revised to evolved pigeonite (Alexander et al., 2016). …”

“…The petrology and bulk chemical analyses of Alexander (2015), Alexander et al. (2016), and Snape et al. (2014) show that the 10 basalt samples have a variety of textures and chemistries and can mostly be classified into recognized Apollo 12 basalt groups.…”