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South Pole-Aitken Basin ejecta reveal the Moon's upper mantle

H. J. Melosh, J. Kendall, B. Horgan, B. C. Johnson, T. Bowling, P. G. Lucey and G. J. Taylor
South Pole-Aitken Basin ejecta reveal the Moon's upper mantle
Geology (Boulder) (December 2017) 45 (12): 1063-1066


The sparse occurrence of the mineral olivine in reflection spectra of the Moon's surface, as well as in deep-seated lunar rocks, has long puzzled lunar geologists because it is expected that the largest impact basins, particularly the 2500-km-diameter South Pole-Aitken (SPA) basin, should have exposed the lunar mantle. Using three-dimensional numerical impact simulations, we show that, even in our most conservative cases, the SPA basin must have sampled the Moon's upper mantle to depths of 100 km and inevitably spewed this material onto the farside highlands. The spectra of this region are, however, dominated by the signature of low-calcium pyroxene (LCP), not olivine. We thus argue that, in contrast to the upper mantle of Earth, the Moon's upper mantle is dominated by LCP. This signature also characterizes the mantle of the large main belt asteroid 4 Vesta and suggests that the current paradigm of olivine-rich planetary upper mantles may require revision.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 45
Serial Issue: 12
Title: South Pole-Aitken Basin ejecta reveal the Moon's upper mantle
Affiliation: Purdue University, Department of Earth, Atmospheric and Planetary Sciences, West Lafayette, IN, United States
Pages: 1063-1066
Published: 201712
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 29
Accession Number: 2018-024437
Categories: Extraterrestrial geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2017360
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Brown University, USA, United StatesUniversity of Chicago, USA, United StatesUniversity of Hawaii at Manoa, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 201806
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