QUANTITATIVE FLUID INCLUSION GAS ANALYSIS OF AIRBURST, NUCLEAR, IMPACT, AND FULGURITE GLASSES

We present quantitative fluid inclusion gas analysis on a suite of violently-formed glasses. We used the incremental crush mass spectrometry method (Norman & Blamey, 2001) to analyze eight pieces of Libyan Desert Glass (LDG). As potential analogues we also analyzed trinitite, three impact crater glasses, and three fulgurites.

The “clear” LDG has the lowest CO₂ content and O₂/Ar ratios are two orders of magnitude lower than atmospheric. The “foamy” glass samples have heterogeneous CO₂ contents and O₂/Ar ratios. N₂/Ar ratios are similar to atmospheric (83.6). H₂ and He are elevated but it is difficult to confirm whether they are of terrestrial or meteoritic origin. Combustion cannot account for oxygen depletion that matches the amount of CO₂ produced. An alternative mechanism is required that removes oxygen without producing CO₂.

Trinitite has exceedingly high CO₂ which we attribute to carbonate breakdown of the caliche at ground zero. The O₂/Ar ratio for trinitite is lower than atmospheric but higher than all LDG samples. N₂/Ar ratios closely match atmospheric.

Samples from Lonar, Henbury and Aouelloul impact craters have atmospheric N₂/Ar ratios. O₂/Ar ratios at Lonar and Henbury are 9.5 to 9.9 whereas the O₂/Ar ratio is 0.1 for the Aouelloul sample.

In most fulgurites the N₂/Ar ratio is higher than atmospheric, possibly due to interference from CO. Oxygen ranges from 1.3 to 19.3%.

Gas signatures of LDG inclusions neither match those from the craters, trinitite nor fulgurites. It is difficult to explain both the observed depletion of oxygen in the LDG and a CO₂ level that is lower than it would be if the CO₂ were simply a product of hydrocarbon combustion in air. One possible mechanism for oxygen depletion is that as air turbulently mixed with a hot jet of vaporized asteroid from an airburst and expanded, the atmospheric oxygen reacted with the metal vapor to form metal oxides that condensed. This observation is compatible with the model of Boslough & Crawford (2008) who suggest that an airburst incinerates organic materials over a large area, melting surface materials that then quench to form glass. Bubbles would contain a mixture of pre-existing atmosphere with combustion products from organic material and products of the reaction between vaporized cosmic materials (including metals) and terrestrial surface and atmosphere.