Premium
Exposure history of glass and breccia phases of lunar meteorite EET87521
Author(s) -
Eugster O.,
Thalmann Ch.,
Albrecht A.,
Herzog G. F.,
Delaney J. S.,
Klein J.,
Middleton R.
Publication year - 1996
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1996.tb02026.x
Subject(s) - meteorite , noble gas , regolith , basalt , breccia , astrobiology , chondrite , geology of the moon , geology , lunar soil , outgassing , lunar mare , geochemistry , mineralogy , astronomy , physics , atomic physics
— Glass‐rich separates were prepared from a sample of the basaltic lunar meteorite EET87521 rich in dark glass. Noble gas isotopic abundances and 26 Al and 10 Be activities were measured to find out whether shock effects associated with lunar launch helped to assemble these phases. Similar 10 Be and 26 Al activities indicate that all materials in EET87521 had a common exposure history in the last few million years before launch. However, the glass contains much higher concentrations of trapped gases and records a much longer cosmic‐ray exposure, 100 Ma–150 Ma, in the lunar regolith than does the bulk sample. The different histories show that the glass existed long before the ejection of EET87521. The trapped 40 Ar/ 36 Ar ratio of 1.6 ± 0.1 implies that the lunar exposure that produced most of the stable cosmogenic noble gases began 500 Ma ago. Cosmogenic and trapped noble gas components correlate strongly in various temperature‐release fractions and phases of EET87521, which is probably because the glass contains most of the gas. The trapped solar ratios, 20 Ne/ 22 Ne = 12.68 ± 0.20 and 36 Ar/ 38 Ar = 5.24 ± 0.05 can be understood as resulting from a mixture consisting of ∼60% solar wind and 40% solar energetic particles (SEP). All EET87521 phases show a 40 K‐ 40 Ar gas retention age of ∼3300 Ma, which is in the range of typical lunar mare basalts.