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On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories
Author(s) -
Vogt S. K.,
Aylmer D.,
Herzog G. F.,
Wieler R.,
Signer P.,
Pellas P.,
Fiéni C.,
Tuniz C.,
Jull A. J. T.,
Fink D.,
Klein J.,
Middleton R.
Publication year - 1993
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1993.tb00250.x
Subject(s) - meteorite , chondrite , ordinary chondrite , stage (stratigraphy) , nuclide , cosmogenic nuclide , geology , mineralogy , analytical chemistry (journal) , astrophysics , chemistry , astrobiology , physics , cosmic ray , nuclear physics , paleontology , environmental chemistry
— We present the 14 C, 26 Al, 10 Be, 3 He, 4 He, 20 Ne, 21 Ne, 22 Ne, 36 Ar, 38 Ar, and 40 Ar 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 14 C, 26 Al, 10 Be, and 21 Ne were: first stage duration ∼10 Ma and radius >2 m; second stage duration ∼0.6 Ma and radius 40–100 cm. Nominal one‐stage 21 Ne production rates (P 21 ) inferred from 26 Al in Bur Gheluai samples exceed those inferred from 10 Be 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 P 21 based on 26 A***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).