Noble gas study of the five Antarctic CK chondrites

Abstract

Metamorphosed chondrites are easy to be marked with in-situ noble gas components such as cosmogenic and neutron capture induced noble gas components because of low abundance of trapped component such as Q gas. Noble gases including 81Kr of CK chondrites EET 13002, 14007, 15156, 15161, 15162, and Karoonda were measured for their CRE ages, size of preatmospheric body, and trapped components. Cosmic-ray exposure ages (CRE ages) of five Antarctic chondrites ranged from 23 - 28 Ma based on cosmogenic 21Ne using empirical equation for production rate of cosmogenic nuclide[1], and terrestrial ages from 81Kr-Kr ages were calculated for the Antarctic meteorites. Neutron capture induced noble gases were clearly observed such as 36Ar, 80, 82Kr, and 128, 131Xe, and size of preatmospheric body of the Antarctic CK chondrites were larger than 47-51 cm based on neutron capture induced 80Kr and 82Kr. It is coincide with high shielding condition of the CK chondrites of low cosmogenic 22Ne/21Ne ratios of 1.056-1.070. Trapped components are composed of Earth atmosphere and Q gas from elemental ratios of heavy noble gas 36Ar/132Xe-84Kr/132Xe corrected after neutron capture induced 36Ar, and incorporation of HL component with Q gas was verified from Xe isotopes.