The Character of South Pole-Aitken Basin: Patterns of Surface and Subsurface Composition

摘要

Using Moon Mineralogy Mapper data, we characterize surface diversity across the enormous South Pole-Aitken Basin (SPA) by evaluating the abundance and composition of pyroxenes, which are overwhelmingly the most abundant mafic mineral in the region. Although SPA exhibits significant complexity due to billions of years of geologic processes subsequent to formation, the basin has retained regular patterns of compositional heterogeneity across its structure. Four distinct, roughly concentric zones are defined: (1) a central SPA compositional anomaly, which exhibits a pervasive elevated Ca,Fe-rich pyroxene abundance; (2) a Mg-pyroxene annulus, which is dominated by abundant Mg-rich pyroxenes; (3) a heterogeneous annulus, which exhibits localized pyroxene-rich areas spatially mixed with feldspathic materials; and (4) the SPA exterior, which is primarily feldspathic. Pyroxene compositions in the heterogeneous annulus are similar to those in the Mg-pyroxene annulus, and Mg-rich pyroxenes also underlie the more Ca,Fe-rich pyroxene surface material across the SPA compositional anomaly. The establishment of these four distinct compositional zones across SPA constrains basin evolution models and serves to guide potential sample return (and other science) targets.