Ejection ages from krypton-81-krypton-83 dating and pre-atmospheric sizes of martian meteorites
Queen Alexandra Range 94201
MetadataShow full item record
CitationEugster, O., Busemann, H., Lorenzetti, S., & Terribilini, D. (2002). Ejection ages from krypton‐81‐krypton‐83 dating and pre‐atmospheric sizes of martian meteorites. Meteoritics & Planetary Science, 37(10), 1345-1360.
PublisherThe Meteoritical Society
JournalMeteoritics & Planetary Science
AbstractCosmic-ray exposure (CRE) ages and Mars ejection times were calculated from the radionuclide 81Kr and stable Kr isotopes for seven martian meteorites. The following 81Kr-Kr CRE ages were obtained: Los Angeles = 3.35 +/- 0.70 Ma; Queen Alexandra Range 94201 = 2.22 +/- 0.35 MA; Shergotty = 3.05 +/- 0.50 Ma; Zagami = 2.98 +/- 0.30 Ma; Nakhla = 10.8 +/- 0.8 Ma; Chassigny = 10.6 +/- 2.0 Ma; and Allan Hills 84001 = 15.4 +/- 5.0 Ma. Comparison of these age with previously obtained CRE ages from the stable noble gas nuclei 3He, 21Ne, and 38Ar shows excellent agreement. This indcates that the method for the production rate calculation for the stable nuclei is reliable. in all martian meteorites we observe effects induced by secondary cosmic-ray produced epithermal neutrons. Epithermal neutron fluxes, phi(n) (30-300 cV), are calculated based on the reaction 79Br(n, gamma x Beta)80Kr. We show that the neutron capture effects were induced in free space during Mars-Earth transfer of the meteorids and that they are not due to a pre-exposure on Mars before ejection of the meteoritic material. Neutron fluxes and slowing down densities experienced by the meteoroids are calculated and pre-atmospheric sizes are estimated. We obtain minimum radii in the range of 22-25 cm and minimum masses of 150-220 kg. These results are in good agreement with the mean sizes reported for model calculations using current semiempirical data.