Projectile-target interaction, melting and vaporization in hypervelocity experiments and natural impactites

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Identification of meteoritic projectile matter as either chemical trace or physical remnant is the only way to assess the past impactor population related to the terrestrial impact record. In the frame of the MEMIN research group this subproject is aimed to reach a better understanding of the parameters that control the fate of projectile and fractionation of meteoritic tracer elements during impact events. This will be achieved by combining (i) hypervelocity experiments with well characterized steel and basaltic projectiles, and sandstone, quartzite, and carbonates as target, (ii) tracing of the very early ejecta stage by time-resolved high-speed spectrometry, (iii) studies on selected natural impactites from the Wabar, Kamil, and Meteor craters, (iv) laser melting experiments, and (v) chemical modelling. In the course of MEMIN I, we were able to demonstrate in ejecta collected from hypervelocity cratering experiment that strong fractionation among meteoritic tracer elements occurs during interaction of projectile and target melts. This project of MEMIN II includes new experimental parameters, such as new target and projectile materials, oblique impact, and new detection techniques to investigate the very early stages of impact. We will study effects of carbonate dissociation, and target melting on the fate of the projectile. Basaltic projectiles will serve as analogue for chondritic and achondritic projectiles in nature. Laser melting experiments are used to constrain the processes of heterogeneous high-temperature melting of target and projectile materials separately. Vaporization of projectile and target material occurs during the very early stages of impact including the jetting stage. The composition and temperature of jetted material will be measured via high-speed spectrometry. The post-mortem analyses using high-sensitive and high resolution analytical tools (LA-ICP-MS, EMP, TEM, INAA) is concentrated to highly shocked ejecta material that turned out in MEMIN I to contain projectile melts and probably condensates. The study of the natural impactites, which has not been done so far with high spatial resolution, is focussed on the comparability of our experimental results to nature. The analysis of platinum group elements (PGE) in >50μm iron-meteoritic melt spheres in the natural impactites by LA ICP MS is a major issue in this project. This is important to understand impact-related fractionation of PGE, which are commonly used to identify the projectile in terrestrial craters. Last not least chemical modelling of the metal-silicate system will be performed to better constrain the effects of temperature and melt composition on the partitioning of the meteoritic tracer elements observed in both, experiments and nature.