¹Libby D. Tunney,¹Patrick J. A. Hill,¹Christopher D. K. Herd,^1,2Robert W. Hilts,¹Miranda C. Holt
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13803]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3 Canada
²Department of Physical Sciences, MacEwan University, Edmonton, Alberta, T6J 4S2 Canada
Published by arrangement with John Wiley & Sons

Soluble organic matter analyses of astromaterials can provide valuable information on the chemistry of our solar system and the processes that occur within it. The surface of the Earth, however, is a significant source of organic compounds due to the presence of life; this environment represents a major source of potential contamination for recently fallen meteorites. Here, we analyze select stones of the CM2 Aguas Zarcas carbonaceous chondrite, which fell on April 23, 2019, in Aguas Zarcas, San Carlos county, Alajuela province, Costa Rica, with the goal of determining the complement of intrinsic and contaminant soluble organic matter. The specimens were collected pre- and post-rainfall, days to weeks after the stones fell on the Earth. Through gas chromatography-mass spectrometry analysis of soluble organic matter in dichloromethane and hot water extracts of meteorite powders, we differentiate between extraterrestrial and contaminant sources for each organic compound detected. In this study, N-tert-butyldimethylsilyl- N-methyltrifluoroacetamide (MTBSTFA) was used to derivatize the hot water extracts to test out its “one-pot” extraction capabilities. The majority of the detectable organic compounds are contaminants and can be explained as being sourced from the terrestrial surface onto which the meteorite fell. Our results have implications for how environmental factors, such as land use and rainfall events in this case, can impact the intrinsic organics in carbonaceous chondrites.

¹Randy G. Hopkins,¹John G. Spray
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13799]
¹Planetary and Space Science Centre, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick, E3B 5A3 Canada
Published by arrangement with John Wiley & Sons

Numerical computing software (via MathWorks MATLAB) has been developed to understand the relationship between shock wave passage in geological targets (i.e., heterogeneous media) and the formation of shock veins and associated high-pressure/temperature polymorphs. This approach takes into consideration the pressure due to the passage of the shock front, subsequent rarefaction unloading pressures, and associated heating and cooling rates. The model is applied to calculate pressure–temperature–time conditions for coesite- and stishovite-bearing shock veins within metaquartzites of the Vredefort impact structure of South Africa. To constrain the model, the position of the host metaquartzites at the time of impact is first reconstructed. The developed code then passes the appropriate shock conditions through the target to re-create the shock wave, while simultaneously forming and cooling the shock veins via 2-D steady-state conduction. We have found that (1) at the time of shock vein formation (2.4 s following the initial contact of the projectile), the shock front pressure was 13.8 GPa and the width of the shock wave was of 27 km; (2) the melt within the shock veins initially reached ~3000 °C, which corresponds to the melting temperature of the target rock at 13.8 GPa. Simulation results indicate that conditions reach the stishovite stability field within 2 ms of vein formation (~10–14 GPa; 2000–3000 °C), followed by coesite within 1.29 s (~3–10 GPa; 600–2000 °C). The dwell time of the modeled shock vein system is 4.35 s. The shock vein system is completely solidified 33.4 s after the initial shock front passage. The calculated P–T–t path of the model indicates that the polymorphs within the shock veins of the metaquartzites at Vredefort formed under their normal stability field conditions following rarefaction wave decompression.