Distribution of the U, Th-He, and K-Ar Ages of Ordinary Chondrites

Details Distribution of the U, Th-He, and K-Ar Ages of Ordinary Chondrites Distribution of the U, Th-He, and K-Ar Ages of Ordinary Chondrites

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.479a&link_type=abstract

Meteoritics, vol. 30, no. 5, page 479

Astronomy and Astrophysics

Astrophysics

Ages, Gas-Retention, Chondrites, Ordinary, Meteorites, Antarctic

Scientific paper

U,Th-He and K-Ar ages of over 700 H, L and LL chondrites were calculated.The noble gas data were taken from [1].The distributions of the ages of all chondrites and,independently, of chondrites having t(sub)3/t(sub)21 <1 within each chemical group were studied (t(sub)3 and t(sub)21 are the 3He and 21Ne cosmic ray exposure ages, respectively). Analysis of the distribution of the 4He and 3He contents in L-chondrites showed the parent body of these meteorites underwent the catastrophic collision in space 350+/-30 Myr ago [2]. This event stipulated the high abundance of L chondrites having low gas-retention ages. As a whole,ages of non-Antarctic finds are less than ages of falls most probably due to losses of noble gases during terrestrial weathering. However,the parameters of the age distributions of Antarctic finds are close to those of falls: storage of meteorites inside ice do not lead to essential losses of gases. Not only L but also H chondrites having low U,Th-He ages tend to have low cosmic-ray exposure ages. Apparently,the most outgassing took place in the events that ejected the meteorites from their parent bodies. The large impacts may produce more outgassing and greater acceleration, leading to a shorter transit time to the Earth [3,4]. The possible difference of thermal history between Antarctic and non-Antarctic meteorites is found. References: [1] Schultz L. and Kruse H. (1989) Meteoritics, 24, 155-172; Schultz L.(1994) personal communication. [2] Alexeev V. A. (1995) LPS XXVI,19-20; Astronom. Vestnik (in Russian), in press. [3] Waenke H. (1966) Fortschr. Chem. Forsch., 7, 322-408. [4] Hintenberger H. et al. (1966) Z. Naturforsch., 21A, 1147-1159.

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