ISOTOPIC ABUNDANCES OF NOBLE GASES IN SOME CHONDRITES AND MESOSIDERITES FELL IN CHINA

Noble gas isotopic abundance of Jiange, Yanzhuang, Bo Xian ordinary chondrites, Weiyuang and recently recovered Deng Ujimqin mesosiderites are measured by the standard procedure and mass spectrometer and results reported in this paper. Based on ³He, ²¹Ne and ³⁸Ar, cosmic-ray exposure ages are calculated. Gas retention ages are determined based on radiogenic ⁴He and ⁴⁰Ar for three chondrites. Cosmic-ray exposure ages of Jiange, Yanzhuang and Bo Xian are 5.8Ma, 2.5Ma and 38.0Ma, respectively. The average ages are 172Ma for Deng Ujimqin and 17Ma for Weiyuang mesosiderites. These ages represent the duration of exposure to cosmic-rays after break-up and ejection from their parent bodies.