Spectral and photogeologic mapping of Schrِdinger Basin and implications for post-South Pole-Aitken impact deep subsurface stratigraphy

Schrödinger Basin provides a window into the stratigraphy of the lunar crust adjacent to the South Pole-Aitken Basin region that we have probed with Lunar Reconnaissance Orbiter, Moon Mineralogy Mapper (M3), and crater-scaling relationships. The composition of materials that make up the basin wall, impact melt, and peak ring provide a cross-section of the lunar crust, which reveals products of the lunar magma ocean, subsequent magmatism, and reworking of those components into a megaregolith. Large hectometer- to kilometer-size areas of anorthite-rich material (anorthosite), low-Ca pyroxene material (a noritic unit), and olivine-rich material (troctolite or dunite) are exposed, with a few areas of intermediate composition. The Schrödinger impact excavated ∼20 km into an orthopyroxene + plagioclase (noritic) lunar crust, which is exposed in the basin walls, rim, and proximal ejecta, and dominates the composition of materials that make up the basin floor. Substantially later in lunar history, two spatially and chronologically isolated volcanic eruptions occurred on the basin floor. Two large craters east of Schrödinger excavated a compositionally gabbroic subsurface unit that was not tapped by Schrödinger. This indicates a compositional crustal facies change, which may be from SPA ejecta, but could reflect heterogeneity in the original lunar crust.