TY - JOUR
T1 - Lunar feldspathic meteorites
T2 - Constraints on the geology of the lunar highlands, and the origin of the lunar crust
AU - Gross, Juliane
AU - Treiman, Allan H.
AU - Mercer, Celestine N.
N1 - Funding Information: We are grateful to A. Peslier for assistance with the EMP analyses, and to C. Goodrich, W. Kiefer, and P. Spudis for advice and helpful discussions. We thank T. Elliot and two anonymous reviewers, for very helpful reviews of this manuscript as well as T. Elliot for handling this manuscript and comments. Supported by NASA Cosmochemistry grant NNX13AF54G to JG and NASA Cosmochemistry grants NNX08AH78G and NNX12AH64G to AHT; LPI contribution #1736.
PY - 2014/2/15
Y1 - 2014/2/15
N2 - The composition of the lunar crust provides clues about the processes that formed it and hence contains information on the origin and evolution of the Moon. Current understanding of lunar evolution is built on the Lunar Magma Ocean hypothesis that early in its history, the Moon was wholly or mostly molten. This hypothesis is based on analyses of Apollo samples of ferroan anorthosites (>90% plagioclase; molar Mg/(Mg + Fe) = Mg# < 75) and the assumption that they are globally distributed. However, new results from lunar meteorites, which are random samples of the Moon's surface, and remote sensing data, show that ferroan anorthosites are not globally distributed and that the Apollo highland samples, used as a basis for the model, are influenced by ejecta from the Imbrium basin. In this study we evaluate anorthosites from all currently available adequately described lunar highland meteorites, representing a more widespread sampling of the lunar highlands than Apollo samples alone, and find that ~80% of them are significantly more magnesian than Apollo ferroan anorthosites. Interestingly, Luna mission anorthosites, collected outside the continuous Imbrium ejecta, are also highly magnesian. If the lunar highland crust consists dominantly of magnesian anorthosites, as suggested by their abundance in samples sourced outside Imbrium ejecta, a reevaluation of the Lunar Magma Ocean model is a sensible step forward in the endeavor to understand lunar evolution. Our results demonstrate that lunar anorthosites are more similar in their chemical trends and mineral abundance to terrestrial massif anorthosites than to anorthosites predicted in a Lunar Magma Ocean. This analysis does not invalidate the idea of a Lunar Magma Ocean, which seems a necessity under the giant impact hypothesis for the origin of the moon. However, it does indicate that most rocks now seen at the Moon's surface are not primary products of a magma ocean alone, but are products of more complex crustal processes.
AB - The composition of the lunar crust provides clues about the processes that formed it and hence contains information on the origin and evolution of the Moon. Current understanding of lunar evolution is built on the Lunar Magma Ocean hypothesis that early in its history, the Moon was wholly or mostly molten. This hypothesis is based on analyses of Apollo samples of ferroan anorthosites (>90% plagioclase; molar Mg/(Mg + Fe) = Mg# < 75) and the assumption that they are globally distributed. However, new results from lunar meteorites, which are random samples of the Moon's surface, and remote sensing data, show that ferroan anorthosites are not globally distributed and that the Apollo highland samples, used as a basis for the model, are influenced by ejecta from the Imbrium basin. In this study we evaluate anorthosites from all currently available adequately described lunar highland meteorites, representing a more widespread sampling of the lunar highlands than Apollo samples alone, and find that ~80% of them are significantly more magnesian than Apollo ferroan anorthosites. Interestingly, Luna mission anorthosites, collected outside the continuous Imbrium ejecta, are also highly magnesian. If the lunar highland crust consists dominantly of magnesian anorthosites, as suggested by their abundance in samples sourced outside Imbrium ejecta, a reevaluation of the Lunar Magma Ocean model is a sensible step forward in the endeavor to understand lunar evolution. Our results demonstrate that lunar anorthosites are more similar in their chemical trends and mineral abundance to terrestrial massif anorthosites than to anorthosites predicted in a Lunar Magma Ocean. This analysis does not invalidate the idea of a Lunar Magma Ocean, which seems a necessity under the giant impact hypothesis for the origin of the moon. However, it does indicate that most rocks now seen at the Moon's surface are not primary products of a magma ocean alone, but are products of more complex crustal processes.
KW - Ferroan anorthosite
KW - Lunar Magma Ocean
KW - Lunar crust
KW - Lunar highlands
KW - Magnesian anorthosite
KW - Serial magmatism
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U2 - https://doi.org/10.1016/j.epsl.2013.12.006
DO - https://doi.org/10.1016/j.epsl.2013.12.006
M3 - Article
SN - 0012-821X
VL - 388
SP - 318
EP - 328
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -