¹M. J. Rucks,²J. M. Winey,²Y. Toyoda,^2,3Y. M. Gupta,¹T. S. Duffy
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007642]
¹Department of Geosciences, Princeton University, Princeton, New Jersey, 08544 USA
²Institute for Shock Physics, Washington State University, Pullman, Washington, 99164-2816 USA
³Department of Physics, Washington State University, Pullman, Washington, 99164-2816 USA
Published by arrangement with Hohn Wiley & Sons

Apatite is a phosphate mineral relevant to shock metamorphism in planetary materials. Here, we report on the response of natural fluorapatite from Durango, Mexico under shock wave loading between 14.5 and 119.5 GPa. Wave profile measurements were obtained in plate-impact experiments conducted on [0001]-oriented fluorapatite single crystals. To 30 GPa peak stresses, we observed a two-wave structure indicating an elastic-inelastic response with elastic wave amplitudes of 10.5 – 13.1 GPa. Between 39.1 – 62.1 GPa, a complex wave structure was observed involving the propagation of three waves. At and above 73.7 GPa, only a single shock wave was observed. The data above 73.7 GPa provided the following linear shock velocity – particle velocity relationship: Us = 6.5(2) + 0.78(6) up, (mm/μs). Above 80 GPa, the densities in the shocked state exceed both the extrapolated 300-K density of fluorapatite and the predicted 300-K density for a mixture of the high-pressure assemblage, tuite and CaF2. This result indicates that fluorapatite undergoes a transition to a denser structure under shock loading at these conditions. The shock response of fluorapatite is observed to be similar to enstatite but stiffer than quartz and albite at the stresses examined in this work.

^1,2Alison R. Santos,¹Martha S. Gilmore,¹James P. Greenwood,³ Leah M. Nakley,^3,4Kyle Phillips,³Tibor Kremic,¹Xavier Lopez
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007423]
¹Department of Earth and Environmental Sciences, Wesleyan University, 265 Church St., Middletown, CT, 06459 United States
²Previously at: NASA Postdoctoral Program Fellow, NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH 44135
³NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH, 44135 United States
⁴Previously at: HX5 Sierra, LLC, 21000 Brookpark Rd., Cleveland, OH 44135.
Published by arrangement with John Wiley & Sons

We report two experiments using 13 mineral and rock samples exposed to a complex synthetic Venus atmosphere composed of nine gases for durations of 30 and 11 days conducted using the NASA Glenn Extreme Environment Rig (GEER). Examination of our run products using a scanning electron microscope equipped with an energy dispersive spectrometer reveals secondary minerals predominantly formed from reactions of Fe and Ca in the solid samples with sulfur in the atmospheric gas, results largely predicted in the literature, and indicating that such reactions between rocks and the atmosphere at the Venus surface may occur rapidly. Samples that displayed larger degrees of reaction include calcite (forming Ca-sulfate), Fe-Ti oxide (forming an Fe,S phase), biotite (forming an Fe,S phase), chalcopyrite (forming a new Cu,Fe-sulfide and a Ag,Cl phase), and Mid-Ocean Ridge Basalt glass (forming a Ca- and S-bearing phase, Fe- and S-bearing phase, and an Fe-oxide); pyrite was observed to be stable in our 30-day experiment. These reactions indicate that the fS2 of the experiments was above or at the high end of what is thermodynamically predicted for the Venus surface. Apatite, feldspars, actinolite, and quartz did not change in this time frame. The presence of multiple S species in GEER may explain dissimilarities in the style of reactions seen in previous experiments with simpler gas mixtures.