An improved extraction system to measure carbon-14 terrestrial ages of meteorites and pairing of the Antarctic Yamato-75097 group chondrites

Abstract

We examined an improved system for extraction of carbon from meteorites, using a vacuum-tight RF melting method. Meteorite samples mixed with an iron combustion accelerator, including a specific amount of carbon (0.052%), were combusted in a RF furnace (LECO HF-10). 14CO2 extracted from the meteorite was diluted with a known amount of nearly 14C-free CO2, evolved from the iron accelerator on combustion. The 14C activities of the recently fallen Holbrook (L6) and Mt. Tazerzait (L5) meteorites were measured by this method. The mean value was 56.5 +/- 3.0 dpm/kg, which is similar to the values reported for recently fallen L6 chondrites. Furthermore, terrestrial ages were measured for four Antarctic meteorites: 1.8 +/- 0.5 kyr for Yamato (Y-) 75097 (L6), 1.8 +/- 0.5 kyr for Y-75108 (L6), and 0.1 +/- 0.1 kyr for Y-74192 (H5). For Y-74190 (L6), an apparent age of 0.8 +/- 0.5 kyr was calculated. After consideration of the shielding effect by using 22Ne/21Ne values, we obtained about 1.8 kyr for the terrestrial age of this chondrite. The five samples Y-74190, Y-75097, and Y-75108, together with Y-75102 (L6) and Y-75271 (L6), have been reported to be paired and fragments of an L-chondrite shower (Honda 1981; Takaoka 1987). The result of this work and literature data for the latter two samples confirmed that they are paired. More discussion and experimental work are needed for other recently fallen meteorites, both for L and H chondrites, and a correction for the shielding effect should be done to determine a more reliable terrestrial age.