Lunar Crustal KREEP Distribution

IF 3.9 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
J. N. Levin, A. J. Evans, J. C. Andrews-Hanna, I. J. Daubar
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引用次数: 0

Abstract

The distribution of KREEP—potassium (K), rare earth elements (REE), and phosphorus (P)—in the lunar crust is an important clue to deciphering the geochemical and thermal evolution of the Moon. Surface measurements of thorium abundance taken by the Lunar Prospector Gamma Ray Spectrometer (LP GRS) instrument have shown that KREEP is concentrated on the lunar nearside surface, mirroring the hemispheric asymmetry observed in the distribution of maria, crustal thickness, and topography. However, the overall lateral and vertical distribution of KREEP within the crust is poorly constrained, leaving uncertainty in estimates of bulk crustal thorium abundance and in the history and evolution of KREEP. In this study, we compared the overall lateral and vertical distribution of lunar KREEP in the upper crust by determining the thorium abundance of material excavated by complex impact craters. We find that the distribution of KREEP on the nearside is consistent with a layer of high-Thorium ejecta from the Imbrium impact mixing with underlying low-Th (<1 ppm) crustal material, suggesting the excavation of a sub-crustal KREEP reservoir with thorium abundances as high as 45–120 ppm by the Imbrium-forming impact. Imbrium ejecta alone does not explain the distribution of thorium on the lunar farside, particularly around the South Pole Aitken basin, suggesting other sources for farside thorium enrichments. Furthermore, our results refute the existence of a large-scale Thorium-enriched layer in the upper 16 km of the farside crust.

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来源期刊
Journal of Geophysical Research: Planets
Journal of Geophysical Research: Planets Earth and Planetary Sciences-Earth and Planetary Sciences (miscellaneous)
CiteScore
8.00
自引率
27.10%
发文量
254
期刊介绍: The Journal of Geophysical Research Planets is dedicated to the publication of new and original research in the broad field of planetary science. Manuscripts concerning planetary geology, geophysics, geochemistry, atmospheres, and dynamics are appropriate for the journal when they increase knowledge about the processes that affect Solar System objects. Manuscripts concerning other planetary systems, exoplanets or Earth are welcome when presented in a comparative planetology perspective. Studies in the field of astrobiology will be considered when they have immediate consequences for the interpretation of planetary data. JGR: Planets does not publish manuscripts that deal with future missions and instrumentation, nor those that are primarily of an engineering interest. Instrument, calibration or data processing papers may be appropriate for the journal, but only when accompanied by scientific analysis and interpretation that increases understanding of the studied object. A manuscript that describes a new method or technique would be acceptable for JGR: Planets if it contained new and relevant scientific results obtained using the method. Review articles are generally not appropriate for JGR: Planets, but they may be considered if they form an integral part of a special issue.
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