The record of cosmogenic, radiogenic, fissiogenic, and trapped noble gases in recently recovered Chinese and other chondrites

We performed a comprehensive study of the noble gas isotopic abundances in thirty-six chondrites including twenty-seven chondrites recovered in China. The large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter. The comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200°C whereas ≥85% of these gases in carbonaceous chondrites are degassed at ≥ 200°C. There exists a clear correlation of the fraction of trapped Xe released at > 1200°C and petrologic type of chondrites. It thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same. The Ngawi LL3 chondrite is solar gas rich. The solar gases in meteorites and lunar surface material are mixtures of solar wind (SW) and solar energetic particles (SEP). We show that the variations of the 3He4He and 20Ne22Ne ratios for solar gas-rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of He and Ne or due to a change of the SW/SEP flux ratio with time. Furthermore, we demonstrate that the 81Kr concentration is a function of the shielding depth of a sample within the meteoroid. Deviations from this depth dependency curve are observed for Jilin (H5), Lishui (L5), Suizhou (L6), and Dongtai (LL6). A complex exposure history for Jilin is thus confirmed and is possible for the other three chondrites. Cosmic-ray exposure ages are calculated based on six different nuclides—3He, 21Ne, 38Ar, 83Kr, 126Xe, and 81Kr-Kr. In most cases good agreement is observed for the ages derived from the different methods. Quality classes are assigned to the exposure ages, and the age distributions are discussed. In some meteorites we observe effects induced by secondary cosmicray-produced neutrons. Epithermal neutron fluxes, Jn(30–300 eV), and fast neutron fluxes, Jn(>5 MeV), are derived based on the reactions 79Br(n, γβ)80Kr and 24Mg(n, α)21Ne, respectively; and preatmospheric masses of the meteoroids are estimated. We show that the ratio Jn(30–300 eV)Jn(> 5 MeV) increases with increasing preatmospheric mass. We introduce a 3He exposure age/21Ne exposure age vs. 4He gas retention age/40Ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids. Finally, in some chondrites we observe Xe produced by 244Pu fission and calculate the time span between fission-Xe retention in these chondrites and that of the Angra dos Reis achondrite. We find that the ordinary chondrites started to retain fission Xe 48 ± 30 Ma earlier than Angra dos Reis; we do not observe systematic differences between H, L, and LL or type 5 and 6 chondrites with respect to the time of fission Xe retention.