Exposure Ages, Noble Gases and Nitrogen in the Ordinary Chondrite Karimati (L5)

Noble gas and nitrogen isotopic compositions of Karimati ordinary (L5) chondrite are presented. Aliquots of the meteorite were studied in two noble gas mass spectrometers. Its cosmic ray exposure (CRE) history, trapped noble gases and nitrogen isotopic systematic are examined. The compositions of Ne and Kr in this meteorite indicate presence of mixture of solar wind and Q trapped components. In addition to the primordial components, radiogenic 129Xe (from the decay of short-lived radioactive 129I) is observed in the two aliquots (129Xe/132Xe ranges between 1.054 and 1.311). The U/Th-4He and K-40Ar ages are discordant. U/Th-4He ages are younger than the K-40Ar ages, indicating loss of helium. The trapped N component is isotopically light analogous to Q gas/solar wind. The cosmic-ray exposure ages of the two aliquots are 16.1 ± 2.7 Ma and 16.6 ± 2.0 Ma based on the cosmogenic 21Nec and 38Arc concentrations.