On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories |
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| Authors: | S K Vogt D Aylmer G F Herzog R Wieler P Signer P Pellas C Fini C Tuniz A J T Jull D Fink J Klein R Middleton |
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| Institution: | S. K. Vogt,D. Aylmer,G. F. Herzog,R. Wieler,P. Signer,P. Pellas,C. Fiéni,C. Tuniz,A. J. T. Jull,D. Fink,J. Klein,R. Middleton |
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| Abstract: | Abstract— We present the 14C, 26Al, 10Be, 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, 38Ar, and 40Ar concentrations and the track densities measured in up to 13 samples of the Bur Gheluai (H5) meteorite fall. Only a multi-stage exposure history can explain the data in a self-consistent way. Parameters for a model two-stage history obtained by simultaneous, least-squares fitting of the concentrations of 14C, 26Al, 10Be, and 21Ne were: first stage duration ～10 Ma and radius >2 m; second stage duration ～0.6 Ma and radius 40–100 cm. Nominal one-stage 21Ne production rates (P21) inferred from 26Al in Bur Gheluai samples exceed those inferred from 10Be as expected for a meteorite with a complex history. Nonetheless, data for other meteorites indicate that multi-stage irradiations alone do not account for all the high reported values of P21 based on 26A***l: The equations describing the production of cosmogenic nuclides show that uncorrected shielding effects may also play a role. A compilation of ordinary, solar-gas-poor chondrites for which two-stage histories have been proposed includes many with short second stages but none with unambiguously long first stages (>0.2 Ga). |
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