The mineral apatite, Ca₅(PO₄)₃(F,Cl,OH), is a ubiquitous accessory mineral, with its volatile content and isotopic compositions used to interpret the evolution of H₂O on planetary bodies. During hypervelocity impact, extreme pressures shock target rocks resulting in deformation of minerals; however, relatively few microstructural studies of apatite have been undertaken. Given its widespread distribution in the solar system, it is important to understand how apatite responds to progressive shock metamorphism. Here, we present detailed microstructural analyses of shock deformation in ~560 apatite grains throughout ~550 m of shocked granitoid rock from the peak ring of the Chicxulub impact structure, Mexico. A combination of high‐resolution backscattered electron (BSE) imaging, electron backscatter diffraction mapping, transmission Kikuchi diffraction mapping, and transmission electron microscopy is used to characterize deformation within apatite grains. Systematic, crystallographically controlled deformation bands are present within apatite, consistent with tilt boundaries that contain the <c> (axis) and result from slip in <> (direction) on (plane) during shock deformation. Deformation bands contain complex subgrain domains, isolated dislocations, and low‐angle boundaries of ~1° to 2°. Planar fractures within apatite form conjugate sets that are oriented within either {, {, {, or . Complementary electron microprobe analyses (EPMA) of a subset of recrystallized and partially recrystallized apatite grains show that there is an apparent change in MgO content in shock‐recrystallized apatite compositions. This study shows that the response of apatite to shock deformation can be highly variable, and that application of a combined microstructural and chemical analysis workflow can reveal complex deformation histories in apatite grains, some of which result in changes to crystal structure and composition, which are important for understanding the genesis of apatite in both terrestrial and extraterrestrial environments.

中文翻译：

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Chicxulub撞击坑峰环的冲击形变磷灰石的高分辨率显微组织和成分分析

磷灰石矿物Ca ₅（PO ₄）₃（F，Cl，OH）是一种普遍存在的辅助矿物，其挥发性成分和同位素组成可用于解释H ₂的演化O在行星体上。在超高速撞击中，极高的压力会冲击目标岩石，从而导致矿物变形。然而，磷灰石的微观结构研究相对较少。鉴于其在太阳能系统中的广泛分布，重要的是要了解磷灰石如何响应渐进的冲击变质。在这里，我们介绍了从墨西哥Chicxulub冲击结构的峰顶到整个550 m的冲击花岗岩中约560 m磷灰石晶粒的冲击变形的详细微观结构分析。高分辨率背向散射电子（BSE）成像，电子背向散射衍射图谱，透射菊池衍射图谱和透射电子显微镜相结合，用于表征磷灰石晶粒内的变形。系统性c >（轴），是由于在冲击变形期间在（平面）上在< >（方向）上打滑而导致的。形变带包含复杂的亚晶粒域，孤立的位错和约1°至2°的低角度边界。磷灰石内的平面裂缝形成共轭集，其取向位于{ ，{ ，{或。对一部分再结晶和部分再结晶的磷灰石晶粒进行的补充电子微探针分析（EPMA）表明，冲击再结晶的磷灰石成分中MgO含量存在明显变化。这项研究表明，磷灰石对冲击变形的响应可能是高度可变的，并且结合使用微结构和化学分析工作流程可以揭示磷灰石晶粒中复杂的变形历史，其中一些会导致晶体结构和组成发生变化，对于了解陆地和陆地外环境中磷灰石的成因非常重要。