Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow

Abstract

We have investigated seven micrometeorites (MMs) from Antarctic snow collected in 2003 and 2010 by means of electron microscopy, X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy (TEM) observation, and noble-gas isotope analysis. Isotopic ratios of He and Ne indicate that the noble gases in these MMs are mostly of solar wind (SW). Based on the release patterns of SW 4 He, which should reflect the degree of heating during atmospheric entry, the seven MMs were classified into three types including two least heated, three moderately heated, and two severely heated MMs. The heating degrees are well correlated to their mineralogical features determined by TEM observation. One of the least heated MMs is composed of phyllosilicates, whereas the other consists of anhydrous minerals within which solar flare tracks were observed. The two severely heated MMs show clear evidence of atmospheric heating such as partial melt of the uppermost surface layer in one and abundant patches of dendritic magnetite and Si-rich glass within an olivine grain in the other. It is noteworthy that a moderately heated MM composed of a single crystal of olivine has a 3 He/

Origin of Light Noble Gases (He, Ne, and Ar) on Earth: A Review

“… 20 Ne/ 22 Ne versus (a) the heating index and (b) the 22 Ne content for some IDPs (Kehm et al, ) and micrometeorites (Bajo et al, ; Marty et al, ; Okazaki et al, ). Bajo et al (), Okazaki et al (), and Marty et al () only characterized the heating degree of their samples and we then attributed a heating index between 1 and 3 to compare with the index of Kehm et al () (see text and also supporting information Figure S‐5). IDPs are in blue and micrometeorites in orange.…”

“…IDPs and micrometeorites are also exposed to solar wind irradiation during their transport in the solar system and may also reflect the implanted solar wind composition. Several studies report the noble gas isotopic compositions of IDPs (Hudson et al, 1981;Kehm et al, 2006;Nier & Schlutter, 1990, 1992Pepin et al, 2000Pepin et al, , 2001 and of micrometeorites (Bajo et al, 2012;Marty et al, 2005;Okazaki et al, 2015;Osawa et al, 2000Osawa et al, , 2003Osawa & Nagao, 2002a, 2002b. However, the uncertainties on the neon and argon data are big and these particles have lost a fraction of their noble gases due to heating in the Earth's atmosphere (Bajo et al, 2012;F€ uri et al, 2013;Kehm et al, 2006;Marty et al, 2005;Okazaki et al, 2015;Osawa et al, 2003).…”

“…Some studies tried to define the extent of atmospheric heating for their samples (Bajo et al, 2012;Kehm et al, 2006;Okazaki et al, 2015). Kehm et al (2006) even determined a heating index from 1 to 3 based on the He and Zn contents.…”

“…Kehm et al (2006) even determined a heating index from 1 to 3 based on the He and Zn contents. To compare with the heating degree mentioned by Bajo et al (2012) estimated according to mineral composition and that of Okazaki et al (2015) determined by the solar 4 He release pattern, we attribute a value of 1 for weak or least heating, a value of 1.5 for weak to moderate heating, a value of 2 for moderate heating and a value of 3 for severe heating, as described by Bajo et al (2012) and Okazaki et al (2015). For the samples studied by Marty et al (2005), we attribute a value of 1 for the crystalline samples, a value of 1.5 for scoria/crystalline samples, a value of 2 for scoria samples, of 2.5 for scoria/cosmic spherule samples, and of 3 for cosmic spherules.…”

Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

“…which deposited on surface, pressed, frozen and encapsuled as archives of long-term climate change and episodic events. Ice cores also contain various solid particles such as eolian dust, volcanic ash and extraterrestrial materials (e.g., Misawa et al 2010;Okazaki et al 2015). Volcanic ash could be marker horizons representing events associated with volcanic eruptions in relatively short period of time (typically a year to several years).…”