title: Discovery of seifertite in a shocked lunar meteorite.
abstract: Many craters and thick regoliths of the moon imply that it has experienced heavy meteorite bombardments. Although the existence of a high-pressure polymorph is a stark evidence for a dynamic event, few high-pressure polymorphs are found in a lunar sample. α-PbO₂-type silica (seifertite) is an ultrahigh-pressure polymorph of silica, and is found only in a heavily shocked Martian meteorite. Here we show evidence for seifertite in a shocked lunar meteorite, Northwest Africa 4734. Cristobalite transforms to seifertite by high-pressure and -temperature condition induced by a dynamic event. Considering radio-isotopic ages determined previously, the dynamic event formed seifertite on the moon, accompanying the complete resetting of radio-isotopic ages, is ~2.7 Ga ago. Our finding allows us to infer that such intense planetary collisions occurred on the moon until at least ~2.7 Ga ago.
authors.affiliation: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. miyahara@m.tohoku.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Miyahara
authors.forename: Shohei
authors.initials: S
authors.lastname: Kaneko
authors.forename: Eiji
authors.initials: E
authors.lastname: Ohtani
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakai
authors.forename: Toshiro
authors.initials: T
authors.lastname: Nagase
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kayama
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Nishido
authors.forename: Naohisa
authors.initials: N
authors.lastname: Hirao