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

破碎锥体是唯一可以在宏观尺度上容易识别的冲击(冲击)指标。因此，它们是确认古代侵蚀陨石坑的重要诊断工具。这一建议旨在通过严格的实验分析，并与德国施泰因海姆陨石坑的天然破碎锥进行比较，更好地约束破碎锥的形成条件。关于它们形成所需的物理边界条件，仍然没有达成共识。我们打算应用在MEMING程序中建立的数值模型来确定冲击压力、压力长度和压力分布、应力和应变张量以及应变率。此外，对于破碎锥体是如何形成的，目前还没有达成共识，断裂表面是剪切破坏还是拉伸破坏仍存在争议。我们将首次应用白光干涉和原子力显微镜(AFM)对破碎锥体表面进行完整的形态计量分析。使用扫描电子显微镜、EBSD和透射电子显微镜进行的这种和严格的微观结构分析将被用来破译斯坦海姆陨石坑的实验室和自然破碎锥的形成和破坏机制。以固体岩石为靶材的高能梅明陨石坑实验非常适合于形成和探测破碎锥，因为陨石坑的形成过程被以尽可能高的精度进行监测，并且陨石坑具有分米大小并允许进行详细的空间测量。它的目的是寻找实验室条件，允许可重复和可预测的破碎锥体形成。同样重要的是要界定不形成破碎圆锥的条件。最终目标是为破碎锥的产生推导出一个统一的模型，该模型必须与我们的宏观和微观观测以及所获得的物理边界条件相一致。到目前为止，没有一个已发表的形成模型被普遍接受，它们都不能解释破碎锥体的圆锥形和马尾状分层条纹图案。大多数模型都具有某种非均质性(包裹体、孔隙空间等)的共同点。必须存在于破碎圆锥体的顶端。这种非均质性导致了与围岩的阻抗对比，是球面波干扰标准冲击波的源点。我们质疑这一前提条件，因为粉碎锥体在细粒泥晶石灰岩中特别发育，就像斯坦海姆盆地一样，在那里，任何类型的大型包裹体都可能很少或不存在。

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.