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

Moriarty, D. P.; Pieters, C. M.

doi:10.1002/2017je005364

Cited by 96 publications

(159 citation statements)

References 49 publications

(120 reference statements)

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“…The location of the WCK between the inner depression and inner ring of Crisium suggests that this material is a mixture of feldspathic target material, proximal ejecta, and impact melt/breccia produced during basin formation and evolution. Similar mixtures are observed within the “Heterogeneous Annulus” of the South Pole‐Aitken Basin (Moriarty & Pieters, ).…”

Section: Discussionsupporting

confidence: 69%

Impact Melt Facies in the Moon's Crisium Basin: Identifying, Characterizing, and Future Radiogenic Dating

et al. 2020

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Both Earth and the Moon share a common history regarding the epoch of large basin formation, though only the lunar geologic record preserves any appreciable record of this Late Heavy Bombardment. The emergence of Earth's first life is approximately contemporaneous with the Late Heavy Bombardment; understanding the latter informs the environmental conditions of the former, which are likely necessary to constrain the mechanisms of abiogenesis. While the relative formation time of most of the Moon's large basins is known, the absolute timing is not. The timing of Crisium Basin's formation is one of many important events that must be constrained and would require identifying and dating impact melt formed in the Crisium event. To inform a future lunar sample dating mission, we thus characterized possible outcrops of impact melt. We determined that several mare lava-embayed kipukas could contain impact melt, though the rim and central peaks of the partially lava-flooded Yerkes Crater likely contain the most pure and intact Crisium impact melt. It is here where future robotic and/or human missions could confidently add a key missing piece to the puzzle of the combined issues of early Earth-Moon bombardment and the emergence of life.Plain Language Summary How could life get started on Earth nearly four billion years ago if our planet was constantly being impacted by asteroids and comets? While we do not yet know, we are starting to piece together parts of the answer. Earth's largest impact basins are long gone because of our planet's active geology, life, and flowing water. But the Moon's big craters are well preserved. The formation of those large basins melted lots of rocks, which then cooled; by collecting those rocks on future missions and figuring out how old they are, we can determine the timing of when large basins formed on the Moon and, by extension, on Earth. Crisium basin is one of those large basins that we need to get the age for. Most of the rock that was melted from this impact and then cooled is buried by much younger lava flows, but we believe that some of it was brought up when the crater Yerkes formed on top of Crisium. The central mountain of Yerkes Crater is where we believe future robots and/or astronauts should go to collect once-molten rock and figure out how old it and the basin are.

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Section: Discussionsupporting

confidence: 69%

Impact Melt Facies in the Moon's Crisium Basin: Identifying, Characterizing, and Future Radiogenic Dating

et al. 2020

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“…To restrict the emplacement of mantle materials within the SPA floor may require a much smaller transient crater, which would allow formation of a melt pool within a roughly circular (~400‐ to 500‐km diameter) area near the apparent center of the SPA basin (Ohtake et al, ; Uemoto et al, ). This area approximately corresponds to the SPA compositional anomaly (Moriarty & Pieters, ) and is characterized by abundant Ca, Fe‐rich pyroxenes (Moriarty & Pieters, , ; Ohtake et al, ).…”

Section: Discussionmentioning

confidence: 96%

“…In contrast, the lunar highland rocks are generally much poorer in both iron and titanium, <6 wt% of FeO and <1 wt% of TiO 2 (Dymek et al, ; Taylor et al, ; Warren et al, ), although there is a known mafic impact‐melt component in the lunar highlands (e.g., Ryder & Wood, ). It is possible that the nature of the formation of the SPA basin allowed the formation of impact melt deposits with more iron‐ and titanium‐rich compositions (e.g., Moriarty & Pieters, ) than that sampled by the Apollo and Luna missions. Thus, our analysis is limited to the comparison between known sample compositions and the global remote sensing data set.…”

Section: Discussionmentioning

confidence: 97%

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Geologic History of the Northern Portion of the South Pole‐Aitken Basin on the Moon

et al. 2018

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We conducted a detailed photogeological analysis of the northern portion of the South Pole‐Aitken (SPA) basin (10–60°S, 125–175°W) and compiled a geological map (1:500,000 scale) of this region. Our new absolute model age for the Apollo basin, 3.98 + 0.04/−0.06 Ga, provides a lower age limit for the formation of the SPA basin. Some of the plains units in the study area were formed by distal ejecta from remote craters and basins. The characteristic concentrations of FeO and TiO2 of other plains are indicative of their volcanic origin. The oldest volcanic materials occur near the center of the SPA basin and have an Early Imbrian age of ~3.80 + 0.02/−0.02 Ga. Late Imbrian volcanic activity occurred in and around the Apollo basin. In total, the volcanic plains cover ~8% of the map area and cannot account for the extensive SPA iron signature. The sources of the signature are the oldest materials on the SPA floor (FeO ~11–14.5 wt%). In contrast, the ejecta composing the SPA rim are significantly poorer in FeO (<7.5 wt%). The signature could be related to the differentiation of the SPA impact melt. However, the spatial segregation of the ancient iron‐rich and iron‐poor materials suggests that the SPA iron signature predated the basin. Thus, the signature might be explained by a pre‐SPA lunar crust that was stratified with respect to the iron concentrations, so that the SPA impact excavated the upper, iron‐poorer portion of the crust to form the SPA rim and exposed the deeper, iron‐richer portion on the floor of the basin.

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“…The farside South Pole‐Aitken (SPA) basin is the largest known impact structure on the Moon (Stuart‐Alexander, ; Wilhelms et al, ). Its geology provides insights into the composition of the lower crust and upper mantle, the impact flux in early lunar history, the nature and evolution of basin‐scale impact melt deposits, and the nature of large impact basins and their formation and modification processes (Garrick‐Bethell & Zuber, ; Head et al, ; Moriarty & Pieters, ; Potter et al, ; Spudis et al, ; Vaughan & Head, ). The SPA basin has been studied with spectral observations (e.g., Ohtake et al, ; Pieters et al, ) and recently been subdivided into four distinct compositional zones based on Moon Mineralogy Mapper (M 3 ) data (Moriarty & Pieters, ): (1) a central ~700‐km‐wide SPA compositional anomaly (SPACA), which exhibits a strong Ca‐pyroxene signature, which is different from typical mare basalts; (2) a Mg‐Pyroxene Annulus, which is characterized by Mg‐rich pyroxenes; (3) a Heterogeneous Annulus, which exhibits mixing of localized pyroxene‐rich units and feldspathic materials; and (4) the SPA Exterior, which is mafic‐free and dominated by feldspathic materials.…”

Section: Introductionmentioning

confidence: 99%

Geological Characteristics of Von Kármán Crater, Northwestern South Pole‐Aitken Basin: Chang'E‐4 Landing Site Region

et al. 2018

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Von Kármán crater (diameter = ~186 km), lying in the northwestern South Pole‐Aitken (SPA) basin, was formed in the pre‐Nectarian. The Von Kármán crater floor was subsequently flooded with one or several generations of mare basalts during the Imbrian period. Numerous subsequent impact craters in the surrounding region delivered ejecta to the floor, together forming a rich sample of the SPA basin and farside geologic history. We studied in details the targeted landing region (45.0–46.0°S, 176.4–178.8°E) of the 2018 Chinese lunar mission Chang'E‐4, within the Von Kármán crater. The topography of the landing region is generally flat at a baseline of ~60 m. Secondary craters and ejecta materials have covered most of the mare unit and can be traced back to at least four source craters (Finsen, Von Kármán L, Von Kármán L', and Antoniadi) based on preferential spatial orientations and crosscutting relationships. Extensive sinuous ridges and troughs are identified spatially related to Ba Jie crater (diameter = ~4 km). Reflectance spectral variations due to difference in both composition and physical properties are observed among the ejecta from various‐sized craters on the mare unit. The composition trends were used together with crater scaling relationships and estimates of regolith thickness to reconstruct the subsurface stratigraphy. The results reveal a complex geological history of the landing region and set the framework for the in situ measurements of the CE‐4 mission, which will provide unique insights into the compositions of farside mare basalt, SPA compositional zone including SPA compositional anomaly and Mg‐pyroxene annulus, regolith evolution, and the lunar space environment.

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

Cited by 96 publications

References 49 publications

Impact Melt Facies in the Moon's Crisium Basin: Identifying, Characterizing, and Future Radiogenic Dating

Impact Melt Facies in the Moon's Crisium Basin: Identifying, Characterizing, and Future Radiogenic Dating

Geologic History of the Northern Portion of the South Pole‐Aitken Basin on the Moon

Geological Characteristics of Von Kármán Crater, Northwestern South Pole‐Aitken Basin: Chang'E‐4 Landing Site Region

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