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Noble gases and cosmogenic radionuclides in the Gold Basin L4 chondrite shower: Thermal history, exposure history, and pre‐atmospheric size
Author(s) -
Welten K. C.,
Caffee M. W.,
Leya I.,
Masarik J.,
Nishiizumi K.,
Wieler R.
Publication year - 2003
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.1945-5100.2003.tb01052.x
Subject(s) - chondrite , parent body , geology , radionuclide , noble gas , spallation , meteorite , neutron , mineralogy , radiochemistry , chemistry , astrobiology , nuclear physics , physics , organic chemistry
— We measured the concentrations of the cosmogenic radionuclides 10 Be, 26 Al, 36 Cl, and 41 Ca in the stone and metal fractions of 15 fragments of the Gold Basin L4 chondrite shower, as well as noble gases in 18 Gold Basin fragments. A comparison of 10 Be, 26 Al, and 41 Ca concentrations with calculated production rates from two different models indicates that the Gold Basin samples came from depths of about 10 cm to more than 150 cm in an object with a radius of 3–5 m. As was predicted by recent model calculations, the noble gases show a reversal of the 22 Ne/ 21 Ne ratio at very high shielding. The 21 Ne/ 10 Be and 21 Ne/ 26 Al ratios in most samples are constant and correspond to a 4π exposure age of 18 ± 2 Myr. However, three Gold Basin samples show a 30–120% excess of 21 Ne implying that they were previously exposed close to the surface of the parent body, whereas the other samples were buried several meters deeper. Concentrations of neutron‐capture 36 Ar in most samples are consistent with measured concentrations of neutron‐capture 36 Cl and an exposure age of 18 Myr. Large excesses of neutron‐capture 36 Ar were found in those samples with an excess of 21 Ne, providing additional evidence of a first‐stage exposure on the parent body. The excess of spallation‐produced 21 Ne and neutron‐capture‐produced 36 Ar in these samples indicate a first‐stage exposure of 35–150 Myr on the parent body. The radiogenic 4 He and 40 Ar concentrations indicate a major impact on the parent body between 300 and 400 Myr ago, which must have preceded the impacts that brought the Gold Basin meteoroid to the surface of the parent body and then expelled it from the parent body 18 Myr ago.