language: de

Über die leichten Edelgase in dem Chondriten Kirin

F. Begemann, 0. Braun und H. W. Weber
Max-Planck-Institut fur Chemie (Otto-Hahn-Institut),
Mainz
Z. Naturforsch. 85a, 37—43 (1980);

[eingegangen am 19. November 1979]

[Dedicated to H. Hintenberger on the occasion of his 70th birth]

[About the Light-weight Noble Oases in the Kirin H-chondrites]

Results are reported for the contents of He, Ne, and Ar of three different specimens from the Kirin H-chondrite which, with a recovered weight of about 4000 kg, is the largest known stone meteorite. The concentrations of spallogenic gases cover a range of more than a factor of two; bulk samples with ratios 8He/21Ne, 2 and a FeNi nugget with 3He/38Ar = 8.8 ± 0.6 indicate strong diffusion losses of sHe from the silicates and oftritium from the metal. — Radiogenic 4 He and ^Ar have been affected by diffusion, too, resulting in discordant U/Th-4He- and ^K-^Argas retention ages as well as distinctly different ages for different samples. Stepwise heating experiments show the main release of 4He and 4°Ar to occur at around 800 °C and the difference in the gas contents to be due to differences in the low-temperature part of the gas release curve. — An attempt is made to account for the observed positive correlation between the concentrations of spallogenic and radiogenic noble gas nuclides. Either the diffusion losses of both have occured at the same time which requires a (quasi-)continuous loss due to a small perihelion distance or a catastrophic event late during the cosmic ray exposure history, but more than about 10s years before the fall of the meteorite. As an alternative model it is suggested that the Kirin meteoroid was hot upon the ejection from its parent body. As the subsequent cooling rate of the meteoroid is smallest in the interior the diffusion losses of radiogenic 4He and ^Ar will be largest where the production rate of the cosmogenic nuclides is smallest.

Meteorite sind vor ihrem Fall auf die Erde der