车里雅宾斯克撞击角砾岩的显微结构揭示了榴辉岩中磷橄榄石组合的历史
Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus-Olivine-Assemblages in chondrites
摘要：
钙钛矿磷酸盐矿物的地球化学和结构协会可以提供深入了解母小行星的地质历史，但其形成和变形的过程仍然缺乏约束。在这里，我们提出了一个定量评估的含磷矿物纹理的三个不同的冲击岩性（光，暗，熔融）的车里雅宾斯克（LL 5）普通球粒陨石使用扫描电子显微镜，电子探针，阴极发光，电子背散射衍射技术。相位协会，显微结构和磷酸盐的显微结构是非常可变的内部和之间的不同的冲击岩性在车里雅宾斯克陨石调查。我们观察到连续应变以及再结晶，无应变磷酸盐人口。再结晶颗粒（无应变子域）只存在于更强烈的冲击黑暗的岩性，表明磷酸盐生长在车里雅宾斯克早于初级冲击变质纹理的发展。这一破坏事件也记录了部分陨石的完全熔化，产生冲击熔融岩性，其中包含一个人口的富磷橄榄石颗粒。我们解释的纹理和相协会车里雅宾斯克已导致通过交代橄榄石置换初始磷酸盐生长，随后在早期冲击熔融的影响和随后的轻微冲击事件的主要变形。这个小事件似乎已经产生了一个亚群的磷酸盐，显示片状CL纹理，在光明和黑暗的岩性。最后，我们提出了一个新的分类方案来描述各种类型的磷橄榄石组合（类型I-III POAs），它可以用来分类的冲击变质事件，并定义相关的物理化学过程。
英文摘要：
The geochemistry and textural associations of chondritic phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained. Here, we present a quantitative assessment of phosphorus-bearing mineral textures in the three variously-shocked lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques. Phase associations, microtextures, and microstructures of phosphates are extremely variable within and between the differently-shocked lithologies investigated in the Chelyabinsk meteorite. We observe continuously strained as well as recrystallized, strain-free phosphate populations. Recrystallized grains (with strain-free subdomains) are present only in the more intensely shocked dark lithology, indicating that phosphate growth in Chelyabinsk predates the development of primary shock-metamorphic textures. This disruption event is also recorded by complete melting of portions of the meteorite to produce the shock-melt lithology, which contains a population of phosphorus-rich olivine grains. We interpret the textures and phase associations of Chelyabinsk to have resulted from initial phosphate growth via metasomatic olivine replacement, followed by major deformation during an early shock-melting impact and a subsequent minor shock event. This minor event appears to have generated a sub-population of phosphates that display patchy CL textures, in both the light and dark lithology. Finally, we propose a new classification scheme to describe various types of Phosphorus-Olivine-Assemblages (Type I-III POAs), which can be used to classify shock metamorphic events and define the associated physicochemical processes.
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