The distribution of shock deformation effects, as well as the structural expression of an impact structure, can be asymmetric, depending on target rock lithologies (e.g., layered versus homogenous), porosity of target rock, and angle of impact. Here, we present a detailed study of shock‐deformed quartz and zircon in silicified sandstones from the asymmetric Spider impact structure in Australia. We utilize optical microscopy and electron backscatter diffraction (EBSD) techniques in order to determine the spatial distribution of shock‐deformed zircon along a downrange transect across the central uplift of the structure, with the goal of constraining the physical distribution of shock effects created by an oblique impact. A total of 453 zircon grains from 12 samples of shatter cone‐bearing quartzite and breccia within the structure were surveyed for shock deformation by EBSD in situ within thin sections. Nineteen zircon grains contain {112} twins, including one grain with three twin orientations. Quartz grains from five samples along the transect were also surveyed using a universal stage in order to determine orientations of planar deformation features, planar fractures, and feather features, and to provide a baseline for comparison of data from zircon. The distribution of shocked zircon with {112} twins within the samples surveyed appears to be asymmetric relative to the center of the structure, in contrast to quartz, thus providing the first accessory mineral‐based evidence that supports an asymmetric distribution of shock deformation as a function of impact obliquity. Our results are an example where the highest intensity of observed shock deformation does not correspond to the geographic center of the structure, and may serve as a guide for field studies aimed at documenting the distribution of shock effects at other sites interpreted to result from oblique impacts.

中文翻译：

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西澳大利亚蜘蛛冲击结构的非对称冲击变形

冲击变形效应的分布以及冲击结构的结构表达式可以是不对称的，具体取决于目标岩石的岩性（例如，分层的还是均质的），目标岩石的孔隙度和冲击角。在这里，我们对来自澳大利亚非对称蜘蛛冲击结构的硅化砂岩中的形变石英和锆石进行了详细研究。我们利用光学显微镜和电子背向散射衍射（EBSD）技术来确定沿结构中央隆起的下冲断面变形的锆石的空间分布，目的是限制由撞击产生的冲击效应的物理分布。倾斜冲击。通过EBSD在薄截面内对结构中的12个破碎圆锥状石英岩和角砾岩样品中的总共453个锆石晶粒进行了冲击变形调查。19个锆石晶粒包含{112}个孪晶，其中一个晶粒具有三个孪晶取向。为了确定平面变形特征，平面裂缝和羽化特征的方向，并为比较锆石数据提供了基线，还使用了通用平台对沿该断面的五个样本中的石英晶粒进行了调查。与石英相反，被调查样品中具有{112}孪晶的冲击锆石的分布相对于结构中心而言似乎是不对称的，因此，提供了第一个基于矿物的辅助证据，该证据支持冲击变形随冲击倾角而变化的不对称分布。我们的结果是一个示例，其中观察到的最大震动变形强度与结构的地理中心不对应，并且可以作为野外研究的指南，目的是证明其他倾斜效应造成的震动影响的分布情况。 。