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轻松识别的冲击（冲击）指标。因此，它们是确认古代侵蚀撞击坑的重要诊断工具。该提案旨在通过严格的实验分析并与德国斯坦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、压力长度和分布、应力和应变张量以及应变率。此外，对于破碎锥如何形成还没有达成共识，并且断裂表面是剪切破坏还是拉伸破坏的结果仍然存在争议。我们将首次应用白光干涉测量法和原子力显微镜 (AFM) 对破碎锥表面进行完整的形态分析。这种使用 SEM、EBSD 和 TEM 的严格微观结构分析将用于破译斯坦海姆陨石坑的实验室和天然碎裂锥的形成和破坏机制。使用固体岩石作为目标材料的高能 MEMIN 陨石坑实验特别适合形成和检测碎裂锥，因为陨石坑形成过程以尽可能高的精度进行监测，而且陨石坑的尺寸为分米级，可以进行详细的空间调查。其目的是找到允许可重复且可预测地形成破碎锥的实验室条件。同样重要的是界定破碎锥不形成的条件。最终目标是导出一个统一的破碎锥生成模型，该模型必须与我们的宏观和微观观察以及获得的物理边界条件一致。到目前为止，没有一个已发表的形成模型被普遍接受，并且没有一个模型可以解释破碎锥的圆锥形状和马尾分层条纹图案。大多数模型的共同点是，破碎锥的顶点必须存在某种异质性（夹杂物、孔隙空间等）。这种不均匀性会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。我们对这一先决条件提出质疑，因为碎裂锥在细粒泥晶石灰岩中特别发育，例如在斯坦海姆盆地，其中任何类型的大型包裹体可能都很罕见或不存在。

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.