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Guangnan (L6) and Ningqiang (CV3): Exposure Ages and Radiogenic Ages of Two Unusual Chondrites

 

作者: O. Eugster,   Th. Michel,   S. Niedermann,  

 

期刊: Meteoritics  (WILEY Available online 1988)
卷期: Volume 23, issue 1  

页码: 25-27

 

ISSN:0026-1114

 

年代: 1988

 

DOI:10.1111/j.1945-5100.1988.tb00892.x

 

出版商: Blackwell Publishing Ltd

 

数据来源: WILEY

 

摘要:

Abstract—The isotopic abundances of the noble gases in bulk samples of the Guangnan L6 chondrite and of the anomalous CV3 chondrite Ningqiang were measured. Guangnan yields a cosmic‐ray exposure age of 2.9 ± 0.4 Ma and belongs to the group of L chondrites with low exposure ages. Ningqiang, however, shows a cosmic‐ray exposure age of 42.2 ± 4.0 Ma, the highest for a CV3 chondrite. The concentrations of radiogenic4He and40Ar in Guangnan are the lowest observed in any ordinary chondrite. A U/Th‐4He age of 27 ± 16 Ma and a40K–40Ar age of 142 ± 14 Ma are calculated assuming L chondritic U, Th, and K concentrations. This assumption is justified considering the fact that a mineralogical composition typical for L chondrites was reported for this meteorite. The observed severe gas losses must have occurred at or before the onset of the exposure of the meteoroid to the cosmic radiation. For the Ningqiang carbonaceous chondrite concordant gas retention ages are obtained: The U/Th‐4He age is 4170 ± 160 Ma whereas the40K–40Ar age is 4260 ± 70 Ma, assuming average U, Th, and K concentration

 

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