Noble gas isotopes and mineral assemblages of Antarctic micrometeorites collected at the meteorite ice field around the Yamato Mountains

Abstract

Noble gas isotopes and mineral assemblages of Antarctic micrometeorites collected at the meteorite ice field around the Yamato MountainsAbstract-From November 1998 to January 1999, the 39th Japanese Antarctic Research Expedition (JARE) conducted a large-scale micrometeorite collection at 3 areas in the meteorite ice field around the Yamato Mountains, Antarctica. The Antarctic micrometeorites (AMMs) collected were ancient cosmic dust particles. This is in contrast with the Dome Fuji AMMs, which were collected previously from fresh snows in 1996 and 1997 and which represent modern micrometeorites. To determine the noble gas concentrations and isotopic compositions of individual AMMs, noble gas analyses were carried out using laser-gas extraction for 35 unmelted Yamato Mountains AMMs and 3 cosmic spherules. X-ray diffraction analyses were performed on 13 AMMs before the noble gas measurement and mineral compositions were determined. AMMs are classified into 4 main mineralogical groups, defined from the heating they suffered during atmospheric entry. Heating temperatures of AMMs, inferred from their mineral compositions, are correlated with 4 He concentrations and reflect the effect of degassing during atmospheric entry. Jarosite, an aqueous alteration product, is detected for 4 AMMs, indicating the aqueous alteration during long-time storage in Antarctic ice. Jarosite-bearing AMMs have relatively low concentrations of 4 He, which is suggestive of loss during the alteration.High 3 He/ 4 He ratios are detected for AMMs with high 20 Ne/ 4 He ratios, showing both cosmogenic 3 He and preferential He loss. SEP (solar energetic particles)-He and Ne, rather than the solar wind (SW), were dominant in AMMs, presumably showing a preferential removal of the more shallowly implanted SW by atmospheric entry heating. The mean 20 Ne/ 22 Ne ratio is 11.27 ± 0.35, which is close to the SEP value of 11.2. Cosmogenic 21 Ne is not detected in any of the particles, which is probably due to the short cosmic ray exposure ages. Ar isotopic compositions are explained by 3-component mixing of air, Q, and SEP-Ar. Ar isotopic compositions can not be explained without significant contributions of Q-Ar. SEP-Ne contributed more than 99% of the total Ne. As for 36 Ar and 38 Ar, the abundance of the Q component is comparable to that of the SEP component. 84 Kr and 132 Xe are dominated by the primordial component, and solar-derived Xe is almost negligible.

Micro-spectroscopic characterization of organic and hydrous components in weathered Antarctic micrometeorites

“…In fact, ferrihydrite has been reported in AMMs by Matrajt et al (2001). However, Osawa et al (2003) and Nakamura et al (2001) did not detect goethite or other iron hydroxides by synchrotron X-ray diffraction. Therefore, the Fe 3+ -bearing-hydroxide-like materials may have an amorphous nature with relatively low crystalinity (Nagano et al, 2002).…”

Single grain noble gas analysis of Antarctic micrometeorites by stepwise heating method with a newly constructed miniature furnace

“…7. The Ne isotopic ratios for ice-AMMs by Osawa and Nagao (2002) and Osawa et al (2003a) are also shown for comparison. Most data points are similar to those of ice-AMMs, located on a fractionation line passing through SW-Ne.…”

“…Isotopic compositions of all noble gases for more than 100 individual iceAMMs have been measured using a Nd-YAG laser combined with a low blank and highly sensitive mass spectrometer (e.g. Osawa and Nagao, 2002;Osawa et al, 2000Osawa et al, , 2003aOsawa et al, , b, 2010. Concentrations and isotopic ratios of noble gases in the ice-AMMs reported by them clearly indicated that they were irradiated by solar particles in space, although the duration of the solar gas irradiation might be less than 1 Myr for most AMMs, as suggested by the low concentration of cosmic-ray-produced 21 Ne.…”

Organic and volatile elements in the solar system

“…Noble gases were tentatively studied in IDPs and micrometeorites [135][136][137]. Most of the noble gases were found to be solar (solar wind implantation) although Osawa et al claimed that Xe and Kr in micrometeorites are dominated by a primordial component [137]. Only He was studied in IDPs [135,136].…”

“…Ion probes are massively used to determine isotopic composition, while molecular structure is studied by STXM or EELS. Noble gases were tentatively studied in IDPs and micrometeorites [135][136][137]. Most of the noble gases were found to be solar (solar wind implantation) although Osawa et al claimed that Xe and Kr in micrometeorites are dominated by a primordial component [137].…”