Magnesian anorthosites and a deep crustal rock from the farside crust of the moon

Hiroshi Takeda, A. Yamaguchi, D. D. Bogard, Y. Karouji, Mitsuru Ebihara, M. Ohtake, K. Saiki, T. Arai

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

Among over thirty lunar meteorites recovered from the hot deserts and Antarctica, Dhofar 489 is the most depleted in thorium (0.05 ppm), FeO, and rare earth elements (REE). Dhofar 489 is a crystalline matrix anorthositic breccia and includes clasts of magnesian anorthosites and a spinel troctolite. The Mg / (Mg + Fe) mol% (Mg numbers = 75-85) of olivine and pyroxene grains in this meteorite are higher than those of the Apollo ferroan anorthosites. Such materials were not recovered by the Apollo and Luna missions. However, remote sensing data suggest that the estimated concentrations of Th and FeO are consistent with the presence of such samples on the farside of the Moon. The differentiation trend deduced from the mineralogy of the anorthositic clasts define a magnesian extension of the ferroan anorthosite (FAN) trend constructed from the Apollo samples. The presence of magnesian anorthositic clasts in Dhofar 489 still offers a possibility that the farside trend with magnesian compositions is more primitive than the FAN trend, and may require a revision of this classical differentiation trend. The Ar-Ar age of Dhofar 489 is 4.23 ± 0.034 Gyr, which is older than most Ar ages reported for highland rocks returned by Apollo. The old Ar-Ar age of impact formation of this breccia and the presence of a fragment of spinel troctolite of deep crustal origin suggest that a basin forming event on the farside excavated the deep crust and magnesian anorthosites before formation of Imbrium.

Original languageEnglish
Pages (from-to)171-184
Number of pages14
JournalEarth and Planetary Science Letters
Volume247
Issue number3-4
DOIs
Publication statusPublished - 2006 Jul 30
Externally publishedYes

    Fingerprint

Keywords

  • anorthosite
  • lunar farside
  • lunar meteorite
  • magma ocean
  • spinel troctolite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Takeda, H., Yamaguchi, A., Bogard, D. D., Karouji, Y., Ebihara, M., Ohtake, M., Saiki, K., & Arai, T. (2006). Magnesian anorthosites and a deep crustal rock from the farside crust of the moon. Earth and Planetary Science Letters, 247(3-4), 171-184. https://doi.org/10.1016/j.epsl.2006.04.004