Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997

Details Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997 Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997

Jul 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002m%26ps...37..911o&link_type=abstract

Meteoritics & Planetary Science, vol. 37, no. 7, pp. 911-936 (2002)

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Scientific paper

The noble gases He, Ne, Ar, Kr, and Xe were measured in 27 individual Antarctic micrometeorites (AMMs) in the size range 60 to 250 μm that were collected at the Dome Fuji Station. Eleven of the AMMs were collected in 1996 (F96 series) and sixteen were collected in 1997 (F97 series). One of the F97 AMMs is a totally melted spherule, whereas all other particles are irregular in shape. Noble gases were extracted using a Nd-YAG continuous wave laser with an output power of 2.5-3.5W for about 5 minutes. Most particles released measurable amounts of noble gases. 3He/4He ratios are determined for twenty-six AMMs (0.85-9.65 x 10-4). Solar energetic particles (SEP) are the dominant source of helium in most AMMs rather than solar wind (SW) and cosmogenic He. Three samples had higher 3He/4He ratios compared to that of the solar wind, showing the presence of spallogenic 3He. The Ne isotopic composition of most AMMs resembled that of SEP as in the case of helium. Spallogenic 21Ne was detected in three samples, two of which had extremely long cosmic-ray exposure ages (>100 Ma), calculated by assuming SCR (solar cosmic rays) + GCR (galactic cosmic rays) production. These two particles may have come to Earth directly from the Kuiper Belt. Most AMMs had negligible amounts of cosmogenic 21Ne and exposure ages of less than 1 Ma. 40Ar/36Ar ratios for all particles (3.9-289) were lower than that of the terrestrial atmosphere (296), indicating an extraterrestrial origin of part of the Ar with a very low 40Ar/36Ar ratio plus some atmospheric contamination. Indeed, 40Ar/36Ar ratios for the AMMs are higher than solar wind, SEP, and Q-Ar values, which is explained by the presence of atmospheric 40Ar. The average 38Ar/36Ar ratio of twenty-four AMMs (0.194) is slightly higher than the value of atmospheric or Q-Ar, suggesting the presence of SEP-Ar which has a relatively high 38Ar/36Ar ratio. According to the elemental compositions of the heavy noble gases, Dome Fuji AMMs can be classified into three groups: chondritic (eight particles), air-affected (nine particles), and solar-affected (eight particles). The eight AMMs classified as chondritic preserve the heavy noble gas composition of primordial trapped component due to lack of atmospheric adsorption and solar implantation. The average of 129Xe/132Xe ratio for the sixteen AMMs not affected by atmospheric contamination (1.05) corresponds to the values in matrices of carbonaceous chondrites (~1.04). One AMM, F96DK038, has high 129Xe/132Xe in excess of this ratio. Our results imply that most Dome Fuji AMMs originally had chondritic heavy noble gas compositions, and carbonaceous chondrite-like objects are appropriate candidate sources for most AMMs.

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