Age spectra of zircon and related phases from impactites of late Triassic meteorite impact structures and their ejecta deposits

本提案旨在研究晚三叠世（诺里亚）陨石撞击结构。利用灵敏高分辨率离子微探针（SHRIMP）技术分析来自三个冲击结构的锆石：Manicouagan（100公里Ø）、Saint Martin（40公里Ø）和Rochechouart（23公里Ø）。基于不同陨石坑撞击物和目标岩石锆石特征年龄谱的物源分析将用于研究它们对远端喷出物沉积的贡献。在不列颠哥伦比亚省的诺里亚部分、加拿大新斯科舍省的芬迪盆地和英国西南部，将对全球喷出物层的存在进行测试，该层与马尼加根陨石坑的形成相对应。利用透射电子显微镜和微拉曼光谱对冲击变质锆石和相关多晶物进行详细研究，将补充研究，以改进应用于撞击事件的U-Pb测年技术。本研究的主要目标是建立一种识别远端撞击喷出物沉积物的方法，并改进这些事件的年代测定。对这些关键标志层的识别和分析将完善陨石对地球影响的地层记录，并揭示其潜在的环境影响。

This proposal aims to investigate late Triassic (Norian) meteorite impact structures. Zircons from impactites of three impact structures will be analyzed by the Sensitive High-Resolution Ion Micro-Probe (SHRIMP) technique: Manicouagan (100 km Ø), Saint Martin (40 km Ø) and Rochechouart (23 km Ø). Provenance analyses based on characteristic age spectra of zircons from the different craters’ impactites and target rocks will be used to investigate their contribution to distal ejecta deposits. A test for the existence of a global ejecta layer that corresponds to the formation of the Manicouagan impact crater will be undertaken at Norian sections in British Columbia, in the Fundy basin of Nova Scotia, Canada, and in Southwest Britain. A detailed study of shock-metamorphosed zircons and related polymorphs, using transmission electron microscopy and micro-Raman spectroscopy, will complement the study in order to refine the U-Pb dating technique as applied to impact events. Primary goals of this study are the establishment of a method for the identification of distal impact-ejecta deposits and the refinement of the dating of these events. The identification and analysis of such critical marker horizons will refine the stratigraphic record of meteorite impacts on Earth and unravel their potential environmental effects.