High‐resolution microstructural and compositional analyses of shock deformed apatite from the peak ring of the Chicxulub impact crater
High‐resolution microstructural and compositional analyses of shock deformed apatite from the peak ring of the Chicxulub impact crater
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DOI：
10.1111/maps.13541
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发表时间：
2020-08
影响因子：
2.2
通讯作者：
M. A. Cox;T. Erickson;M. Schmieder;R. Christoffersen;D. Ross;A. Cavosie;P. Bland;D. Kring
中科院分区：
文献类型：
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作者：
M. A. Cox;T. Erickson;M. Schmieder;R. Christoffersen;D. Ross;A. Cavosie;P. Bland;D. Kring
磷灰石Ca5(PO4)3(F，Cl，OH)是一种普遍存在的副矿物，其挥发分和同位素组成可用来解释行星体内H2O的演化。在超高速撞击过程中，极限压力冲击目标岩石，导致矿物变形；然而，对磷灰石的微观结构研究相对较少。鉴于磷灰石在太阳系中的广泛分布，了解磷灰石是如何对渐进的冲击变质作用做出反应是很重要的。在这里，我们给出了来自墨西哥希克苏鲁布撞击构造峰环的~560个磷灰石颗粒在~550米受冲击的花岗岩中冲击变形的详细微观结构分析。结合高分辨率背散射电子(BSE)成像、电子背散射衍射图、透射菊池衍射图和透射电子显微镜对磷灰石颗粒内的变形进行了表征。在磷灰石中存在系统的、结晶控制的变形带，与包含(轴)的倾斜边界一致，并且是在冲击变形过程中在{1̄1̄20}(平面)上沿(方向)滑动的结果。变形带包含复杂的亚晶区、孤立的位错和~1°~2°的小角度边界。磷灰石内的平面断裂形成共轭集合，它们在{2̄110}、{21̄1̄0}、{1̄1̄20}或112̄0内定向。对部分重结晶和重结晶磷灰石颗粒的EPMA分析表明，冲击重结晶磷灰石成分中的氧化镁含量发生了明显的变化。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，应用显微结构和化学分析相结合的工作流程可以揭示磷灰石颗粒中复杂的变形历史，其中一些会导致晶体结构和成分的变化，这对于了解磷灰石在地球和地外环境中的成因非常重要。
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 (axis) and result from slip in (direction) on {1̄1̄20} (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 { 2̄110} , { 21̄1̄0} , { 1̄1̄20} , or 112̄0 . 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.