High precision potassium isotopic study of Chinese Antarctic chondrites
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    Abstract:

    Potassium and other moderately volatile element (MVEs) depletion is a common feature ofplanetary bodiesand can be used to trace different depletion processes. As the precursor materials of asteroids and planets, understanding the MVE patterns of chondrites is also of great significance as without this, the origin, formation and evolution of planetary bodies cannot be fully understood. In this paper,using a recently developed high- precision potassium isotope technique,we report the bulk potassium isotopic compositions of 14 Chinese Antarctic chondrites and 6 observed falls (Murchison, Allende, Ningqiang, Tagish Lake, Xinyang and Banma). The results showa range of δ41K for the 21 carbonaceous chondrites of -0. 62‰±0. 05‰ to 0. 37‰±0. 08‰, with an average of -0. 32‰±0. 24‰ (2SD), which is slightly heavier than that of bulk silicate earth (BSE). The range of δ41K for the 18 ordinary chondrites (excluding one extreme GRV 021603) span from -1. 02‰±0. 05‰ to -0. 61‰±0. 02‰, with an average of -0. 81‰±0. 15‰ (2SD), which is slightly lighter than that of the BSE. Murchison (CM2) and Allende (CV3) have relativelylarge internal variation in δ41K (0. 22‰ and 0. 16‰, respectively) possibly due to the heterogeneity at the 100 mg- scale within the samples caused by aqueous alteration. Parent- body processes (aqueous alteration, thermalmetamorphism and shock metamorphism) cannot explain the observed variations in K isotopic composition of bulk chondrites becauseas a closed- system, the whole asteroid has been affected by isochemical modification. In this work, we found no clear correlation between Kdepletion and K isotopic composition among chondrites of different chemical groups, which is generally consistent with the data recently published by others. The single- stage thermal processes such as evaporation or condensation in the solar nebula cannot be well explained. Nucleosynthetic origin could be a possible explanation. Massive stellar winds and supernova ejecta would inject abundant 41K to the solar nebula, which was preserved in the primitive chondrites. Future research is much needed to resolve this issue.

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Jiang Yun, Piers Koefoed, Wang Kun, Hsu Weibiao.2021. High precision potassium isotopic study of Chinese Antarctic chondrites[J]. Acta Geologica Sinica,95(9):2878-2888

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History
  • Received:April 27,2021
  • Revised:June 03,2021
  • Adopted:
  • Online: August 02,2021
  • Published: