V013-0005
The Triple Oxygen Isotopes of a Bulk Sample from the Apollo 17 Double Drive Tube 73002

Wednesday, 9 December 2020
Poster
Karen G Ziegler1, Zachary D Sharp2, Erick Jason Cano2, Steven Simon1, Charles K Shearer1 and The ANGSA Science Team, (1)Institute of Meteoritics, University of New Mexico, Albuquerque, NM, United States, (2)Dept. of Earth and Space Sciences, University of New Mexico, Albuquerque, NM, United States
Abstract:
The oxygen isotope composition of surface samples from the moon has long been of interest. Near-identical Earth and Moon have been a challenging constraint for lunar formation models.

The recent release of sealed Apollo 17 double drive tube 73001/73002 (ANGSA program) has allowed the analyses of pristine samples by high-precision laser fluorination. Initial analyses were made on rind-scrapings collected from the surface of the upper 1 cm of Station 3 core sample 73002. Future isotopic/petrologic analyses will be made on sieved samples and lithic fragments. One objective of this study is whether effects of solar wind on lunar surface material exist. Loose bulk samples (n=10) and fragments (n=2) (2 - 4 mg each) were analyzed by laser-assisted fluorination and mass spectrometry.

Results show that the average Δ’17O values (Δ'17O = δ'17O - 0.528 × δ'18O) of our lunar material and that of bulk silicate Earth (measured in 10 San Carlos olivine standards) are essentially indistinguishable with Δ'17Olunar = -0.056‰ vs. Δ'17OBSE = -0.053‰. The difference, however, is the Δ'17O variability: Δ'17OBSE 1σ s.d. is 0.0056‰ (-0.061 to -0.046‰), whereas Δ'17Olunar 1σ s.d. is 0.0103‰ (-0.075 to -0.041‰) – nearly twice as large. This difference indicates that even in this 1 cm interval we clearly have oxygen isotopic variability that is most likely due to mineralogical / lithological variations. Once we have petrologically characterized size fractions, we can assess a possible correlation between that and Δ'17O values (as also seen by Cano et al., Nature Geoscience 13, 270–274, 2020).

We will obtain better vertical resolution with samples from individual depth intervals within the 1 cm section, as well as from depth intervals along the entire length of the 73001/73002 core. “Stratigraphic” Δ'17O profiles will show whether or not isotopic changes exist as we move away from the immediate lunar surface. The question of solar wind effects, however, can be answered from our initial results: NO. Solar wind, captured by NASA’s Genesis mission, has Δ’17O-values of ~ -30‰ (McKeegan et al., Science 332, 1528–1532, 2011), and, hence, any small contribution to lunar soils would be easily detectable. However, low solar wind input could be offset by sputtering, which raises the δ18O values (Epstein & Taylor, Proc. LSC 2, 1421-1441, 1971).

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