Structure and formation of shatter cones in experimental and natural impact craters

破碎锥是唯一可以在宏观尺度上容易识别的冲击（撞击）指示器。因此，它们是确认古代侵蚀撞击坑的重要诊断工具。该建议旨在通过严格的实验分析和与德国Steinheim陨石坑的天然破碎锥的比较，更好地约束破碎锥的形成条件。关于其形成所需的物理边界条件，仍然没有达成共识。我们打算通过应用MEMIN程序中开发的数值模型来确定冲击压力、压力长度和剖面、应力和应变张量以及应变率。此外，关于破碎锥是如何形成的还没有达成共识，断裂面是剪切破坏还是拉伸破坏的结果仍然存在争议。我们将进行一个完整的形态学分析的粉碎锥表面的应用，为第一次，白色光干涉，和原子力显微镜（AFM）。使用SEM，EBSD和TEM进行严格的微观结构分析，将用于破译Steinheim陨石坑实验室和自然破碎锥的形成和破坏机制。使用固体岩石作为靶材料的高能MEMIN陨石坑实验特别适合于形成和探测破碎锥，因为陨石坑形成过程受到尽可能高的精度监测，陨石坑有分米大小，可以进行详细的空间调查。其目的是找到实验室条件，允许可再现和可预测的粉碎锥的形成。同样重要的是要界定在哪些条件下不会形成破碎锥。最终的目标是得到一个统一的模型，产生的破碎锥，必须与我们的宏观和微观观察和物理边界条件得到一致。到目前为止，没有一个已发表的形成模型被普遍接受，并提供了一个解释圆锥形和马尾分层条纹图案的破碎锥。大多数模型都有一个共同点，即某种非均质性（包裹体，孔隙空间等）。一定存在于破碎锥的顶点这种不均匀性导致与周围岩石的阻抗对比，并且是干扰标准冲击波的球面波的源点。我们质疑这一先决条件，因为破碎锥是特别发达的细粒泥晶灰岩，在斯泰因海姆盆地，其中任何类型的大型夹杂物大概是罕见的或不存在。

Shatter cones are the only shock (impact) indicators that can be readily identified on the macroscopic scale. They are, therefore, an important diagnostic tool to confirm ancient eroded impact craters. This proposal is aimed at better constraining the formation conditions of shatter cones by rigorous experimental analysis and comparison with natural shatter cones from the Steinheim crater, Germany. There is still no consensus regarding the physical boundary conditions that are required for their formation. We intend to determine shock pressure, pressure length and profile, the stress and strain tensor, and strain rate by applying the numerical models developed in the MEMIN program. Moreover, there is no consensus on how shatter cones form and it has remained controversial whether the fracture surfaces are the result of shear or tensile failure. We will carry out a complete morphometric analysis of shatter cone surfaces by applying, for the first time, white light interferometry, and atomic force microscopy (AFM). This and rigorous microstructural analysis using SEM, EBSD, and TEM will be used to decipher the formation and failure mechanism of laboratory and natural shatter cones from the Steinheim crater. The high-energy MEMIN cratering experiments using solid rocks as target materials are uniquely suited to form and detect shatter cones, as the crater-forming process is monitored with highest possible precision, and the craters have decimeter sizes and allow a detailed spatial survey. It is intended to find laboratory conditions that allow a reproducible and predictable formation of shatter cones. It is likewise important to delimit the conditions at which shatter cones do not form. The final objective is to derive a unified model for the generation of shatter cones that has to be consistent with our macroscopic and microscopic observations and the physical boundary conditions obtained. None of the published formation models is universally accepted so far and provides an explanation for both the conical shape and the horsetail hierarchical striation pattern of shatter cones. Most of the models have in common that some sort of heterogeneity (inclusion, pore space, etc.) must exist at the apex of a shatter cone. This heterogeneity causes an impedance contrast with the surrounding rock and is the source point for a spherical wave that interferes with the standard shock wave. We question this prerequisite because shatter cones are particularly well developed in fine-grained micritic limestones, as in the Steinheim basin, in which any sort of large inclusion is presumably rare or absent.