Cosmic‐ray produced, radiogenic, and solar noble gases in lunar meteorites Queen Alexandra Range 94269 and 94281

Abstract

Abstract— We measured the noble gas isotopic abundances in lunar meteorite QUE 94269 and in bulk‐, glass‐, and crystal‐phases of lunar meteorite QUE 94281. Our results confirm that QUE 94269 originated from the same meteorite fall as QUE 93069: both specimens yield the same signature of solar‐particle irradiation and also the cosmogenic noble gases are in agreement within their uncertainities. Queen Alexandra Range 93069/94269 was exposed to cosmic rays in the lunar regolith for ∼1000 Ma, and it trapped 3.5 × 10−4 cm3STP/g solar 36Ar, the other solar noble gases being present in proportions typical for the solar‐particle irradiation. The bulk material of QUE 94281 contains about three times less cosmogenic and trapped noble gases than QUE 93069/94269 and the lunar regolith residence time corresponds to 400 ± 60 Ma. We show that in lunar meteorites the trapped solar 20Ne/22Ne ratio is correlated with the trapped ratio 40Ar/36Ar, that is, trapped 20Ne/22Ne may also serve as an antiquity indicator. The upper limits of the breccia compaction ages, as derived from the trapped ratio 40Ar/36Ar for QUE 93069/94269 and QUE 94281 are ∼400 Ma and 800 Ma, respectively. We found very different regolith histories for the glass phase and the crystals separated from QUE 94281. The glass phase contains much less cosmogenic and solar noble gases than the crystals, in contrast to the glasses of lunar meteorite EET 87521, that were enriched in noble gases relative to the crystalline material. The QUE 94281 phases yield a 40K‐40Ar gas retention age of 3770 Ma, which is in the range of that for lunar mare rocks.