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

鉴定陨星抛射物的化学痕迹或物理残余物是评估与陆地撞击记录有关的过去撞击者数量的唯一方法。在MEMIN研究小组的框架下，这个子项目旨在更好地理解在撞击事件中控制弹丸命运和陨石示踪元素分划的参数。这将通过以下几个方面来实现：(i)以特征明确的钢铁和玄武岩抛射物以及砂岩、石英岩和碳酸盐为目标的超高速实验，（ii）通过时间分辨高速光谱法追踪非常早期的喷射阶段，（iii）研究来自Wabar、Kamil和Meteor陨石坑的选定自然撞击物，（iv）激光熔化实验，以及(v)化学建模。在MEMIN I的过程中，我们能够在超高速弹坑实验中收集的弹射物中证明，在弹丸和目标熔体相互作用过程中，陨石示踪元素之间会发生强烈的分裂。MEMIN II项目包括新的实验参数，如新的靶材和弹丸材料、倾斜撞击和新的探测技术，以研究撞击的早期阶段。我们将研究碳酸盐解离和靶熔化对弹丸命运的影响。玄武岩抛射体在性质上类似于球粒抛射体和无球粒抛射体。采用激光熔化实验分别对靶材和弹丸材料的非均质高温熔化过程进行了约束。弹丸和靶材的汽化发生在撞击的早期阶段，包括喷射阶段。喷射材料的成分和温度将通过高速光谱测定。使用高灵敏度和高分辨率分析工具（LA-ICP-MS， EMP， TEM， INAA）进行的事后分析集中在MEMIN I中含有弹丸熔体和可能凝聚物的高冲击弹射材料上。对自然撞击的研究，目前还没有高空间分辨率的研究，主要集中在我们的实验结果与自然的可比性上。利用LA ICP MS分析天然撞击物中bbb50 μm铁陨石熔体中铂族元素（PGE）的含量是本项目研究的重点。这对于理解与撞击相关的PGE分值很重要，PGE分值通常用于识别地球陨石坑中的抛射物。最后，同样重要的是，将进行金属硅酸盐系统的化学建模，以更好地约束温度和熔体成分对在实验和自然界中观察到的陨石示踪元素分配的影响。

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.