University of Rochester, Department of Earth and Environmental Sciences
As part of a larger study looking to identify and quantify the effects shock metamorphism has on the diffusion of radiogenic geochronometers, researchers travelled to Johnson Space Center to utilize the Flat Plate Accelerator (FPA) to simulate a meteorite impact to the samples. This portion of the study is meant to characterize the morphology of the zircons after the experimental shock.
Two samples were were prepared for our experiment. The first sample was entirely Keuhl Lake zircons, while the second sample was a mixture of a well characterized Bishop Tuff sanidine and Keuhl Lake zircons. The second sample was ~95% sanidine (115 mg) and ~5% zircon (5 mg). Ian Szumila prepared the zircons, used in both samples, by cutting large zircon grains in half and crushing one half of each grain. The remaining halves were saved for future work. Szumila also crushed the sanidine used in sample 2. Each crushed mineral was sieved through a series of mesh sizes and the fractions separated. All grains used in this experiment were from the 150 - 250 micron fractions.
Sample 1 was shocked with 28.4 GPa, whereas sample 2 was shocked with 23.8 GPa. The reduction in pressure, between sample 1 and sample 2, was because the flyer plate of the target housing for sample 1 was blown off during the "shot". This resulted in an almost complete loss of sample 1; however, as you will see below, information was still gained from this sample. Between shots the interior of the FPA is vacuumed out. This meant that the debris from sample 1 could be collected for analysis. Through use of a Light Microscope (LM) and a Scanning Electron Microscope (SEM) it was determined that the debris from sample 1 was composed primarily of melted Teflon (from the projectile used for the impact), metal from the target, and an ash-like substance that had trace amounts of zirconium.