Exposure of Allan Hills 84001 and other achondrites on the Antarctic ice

• Published in: Meteoritics & Planetary Science
• Main Authors: KräHENBÜHL, U., NOLL, K., DÖBELI, M., GRAMBOLE, D., HERRMANN, F., TOBLER, L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1998
• Subjects: Space and Planetary Science; Geophysics; Allan Hills; Antarctic; The Antarctic; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1111/j.1945-5100.1998.tb01671.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1945-5100.1998.tb01671.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.1998.tb01671.x

Abstract— The enrichment of F on Antarctic meteorites is the result of their exposure to the atmosphere, and its measurement allows a subdivision of the terrestrial age into a duration of exposure on the ice and the time a meteorite was enclosed by the ice. In many cases, the periods of surface exposure are only small fractions of the terrestrial ages of meteorites collected in Antarctica. The enrichment of F on the surfaces of Antarctic achondrites was investigated by means of nuclear reaction analysis (NRA): scanning proton beams with an energy of 2.7 and 3.4 MeV were used to induce the reactions 19 F(p,αγ) 16 O and 19 F(p, p'γ) 19 F, respectively. Gamma signals proportional to the F content were measured. The following Antarctic achondrites were investigated: Martian meteorite ALH 84001; diogenite ALHA77256; the eucrites ALHA81011 and ALHA78132; and in addition, the H5 chondrite ALHA79025. For ALH 84001, our data indicate a period of exposure on the ice of <500 years. Thus, this specimen was enclosed in the ice >95% of its terrestrial age of 13 000 years.