Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p43a..03k&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P43A-03
Other
[5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
One of the most prominent regional concentrations of noritic material on the Moon is in the South Pole-Aitken (SPA) basin. In addition to the overall noritic signature of much of the basin interior, prominent exposures of spectrally immature noritic materials are associated with large craters in SPA and are readily observed along the crater walls, within central peaks or in fresh craters on the floors of these larger craters. Because the mafic mineralogy of norite is overwhelmingly dominated by orthopyroxene, it is possible to use spectral properties of norites to estimate the Mg’ (Mg’=Mg/(Mg+Fe) of the pyroxenes in the rocks. We here use global-mode data from the Moon Mineralogy Mapper to characterize the composition of norites throughout SPA. We identify broad compositional trends in SPA and assess whether they are spatially significant, classifying each site as dominated by high- (Mg’>75), medium- (Mg’50-75), or low- (Mg’<50) magnesium pyroxene. Initial results for the eastern portion of SPA suggest that the majority of compositions are of moderate-iron content (~Mg’50-75). However, Dryden and Chaffee S craters, both located in the interior of the Apollo Basin, exhibit absorption bands typical of pyroxenes with significantly higher-Mg content. These results support the hypothesis of Petro et al., [2010] that the Apollo Basin tapped a different composition material than other smaller impacts into the SPA melt sheet. The 480 km diameter, pre-Nectarian Apollo basin is located on the edge of SPA, and sits above some of the thinnest crust on the Moon [Ishihara et al., 2009; Petro et al., 2010]. The most noritic portions of Dryden crater are exposed along the eastern wall of Dryden crater, closest to the inner ring of Apollo, and Chaffee S also lies near the inner ring [Klima et al., 2010]. There are several hypotheses being considered to explain the more magnesian character of these low-Ca pyroxenes. Given the thin nature of the crust at Apollo, and the positioning of the high-Mg detections on the inner ring of the basin, Apollo may have excavated deeper primary crustal (or mantle) material than is exposed elsewhere in SPA. Alternatively. If SPA is covered by a differentiated melt sheet, the Apollo basin may have excavated material from a more magnesian cumulate pile at its base. Finally, it is possible that Apollo impacted a local Mg-rich intrusion, emplaced after the SPA-forming impact.
Head James W.
Isaacson Peter
Klima Rachel L.
Petro Noah E.
Pieters Carlé M.
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