Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

Abstract

[1] Using high-spectral and -spatial resolution Moon Mineralogy Mapper data, we investigate compositional variations across the central peak structures of four impact craters within the South Pole-Aitken Basin (SPA). Two distinct causes of spectral diversity are observed. Spectral variations across the central peaks of Bhabha, Finsen, and Lyman are dominated by soil development, including the effects of space weathering and mixing with local materials. For these craters, the central peak structure is homogeneous in composition, although small compositional differences between the craters are observed. This group of craters is located within the estimated transient cavity of SPA, and their central uplifts exhibit similar mafic abundances. Therefore, it is plausible that they have all uplifted material associated with melts of the lower crust or upper mantle produced during the SPA impact. Compositional differences observed between the peaks of these craters reflect heterogeneities in the SPA subsurface, although the origin of this heterogeneity is uncertain. In contrast to these craters, Leeuwenhoek exhibits compositional heterogeneity across its central peak structure. The peak is areally dominated by feldspathic materials, interspersed with several smaller exposures exhibiting a mafic spectral signature. Leeuwenhoek is the largest crater included in the study and is located in a region of complex stratigraphy involving both crustal (feldspathic) and SPA (mafic melt and ejecta) materials. The compositional diversity observed in Leeuwenhoek's central peak indicates that kilometer-scale heterogeneities persist to depths of more than 10 km in this region.

Evidence of impact melt sheet differentiation of the lunar South Pole‐Aitken basin

“…Vaughan and Head [] suggested that the stratigraphy of the SPA impact melt was differentiated into norite, LCP‐rich pyroxenite, and dunite layers from top to bottom. They suggested that the modeled stratigraphy is consistent with the rock types of central peaks observed in previous studies [ Tompkins and Pieters , ; Nakamura et al , ; Moriarty et al , ; Yamamoto et al , ]. However, the rock type of the top layer of their estimated stratigraphy (norite, which is plagioclase‐rich lithology containing LCP) and that of our observation (HCP‐rich pyroxenite based on average FeO abundance) are inconsistent.…”

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

“…In general, SPA materials are enriched in mafic minerals relative to the highlands feldspathic crust (e.g., Lawrence et al, ; Pieters et al, ). Across the basin, the most common nonmare mafic component appears to be Mg‐rich, low‐Ca pyroxenes (Mg‐Px) (Cahill et al, ; Klima, Pieters, et al, ; Moriarty et al, ; Nakamura et al, ; Pieters et al, ; Tompkins & Pieters, ). The pervasive nature of these Mg‐pyroxene‐rich materials across the basin suggests that they are a result of SPA formation, either as impact melt (e.g., Nakamura et al, ; Vaughan & Head, ) or excavated materials from the lower crust and/or upper mantle (Blewett et al, ; Klima, Dyar, & Pieters, ; Lucey et al, ; Moriarty & Pieters, ; Ohtake et al, ; Pieters et al, ).…”

The nature and origin of Mafic Mound in the South Pole‐Aitken Basin

“…Our analyses focus on the properties of this structure. Central peaks of large complex craters within SPA typically exhibit significant low-Ca pyroxene (LCP) ( Figure S2d), although some variation in pyroxene abundance and composition is observed [Tompkins and Pieters, 1999;Pieters et al, 2001;Cahill et al, 2009;Nakamura et al, 2009;Klima et al, 2011b;Moriarty et al, 2013]. Several asymmetric slopes emanate radially from the central depression: gradual, elongated slopes to the north and west and sharper slopes to the south and east.…”