The Next Step in Unravelling the Earth's Impact History: (U-Th)/He Dating of Impact Structures

解开地球撞击历史的下一步：撞击结构的 (U-Th)/He 年代测定

• 批准号: 0948143
• 负责人: Kip Hodges
• 金额: $ 30.66万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948143&HistoricalAwards=false
• 关键词: Next; Step; Unravelling; Earth; Impact

Asteroids and comets have bombarded the planets of the Solar System for billions of years. Here on Earth, active geological processes have either destroyed or hidden about 90% of these impact craters, and thus far, only 176 impact structures have been identified. In recent years the scientific community has realized the importance of impact events on Earth?s geological and biological history, including the 65 million years old dinosaur mass extinction event that is linked to the large Chicxulub impact crater. Therefore, determining accurate and precise ages of these known impact events is vital in our understanding of the Earth's history. Unfortunately, about 80% of identified terrestrial impact structures are of unknown or only approximately known age because the application of traditional dating techniques is not uniformly successful. This project represents the application of a new dating technique, which in preliminary studies has shown great promise for improving our understanding of the extraterrestrial impact history on Earth. Specifically, this project will involve the use of the (U-Th)/He geochronological technique to date individual U- and Th-bearing crystals (e.g., zircon and apatite) from impact materials from 20 small, medium and large impact structures. The unique properties of the radiogenic daughter product (4He), i.e., its low closure temperature and high diffusivity, make the (U-Th)/He technique ideal for dating the brief, but very intense, thermal and shock metamorphism episode associated with the formation of impact structures. This project involves a national and international team of scientists from 8 countries and 13 scientific institutions, who will provide impact structure samples and expertise to test this hypothesis.

小行星和彗星已经轰炸了太阳系的行星数十亿年。 在地球上，主动地质过程已经破坏或隐藏了约90％的影响陨石坑，到目前为止，仅确定了176个影响结构。 近年来，科学界已经意识到影响事件对地球的地质和生物历史的重要性，其中包括与大型Chicxulub撞击火山口相关的6500万年历史的恐龙质量灭绝事件。 因此，确定这些已知影响事件的准确和精确的年龄对于我们对地球历史的理解至关重要。 不幸的是，由于传统约会技术的应用并非统一成功，约有80％的识别陆地撞击结构是未知或大约已知的年龄。 该项目代表了一种新的约会技术的应用，在初步研究中，该技术在提高我们对地球外影响历史的理解方面表现出了巨大的希望。 具体而言，该项目将涉及使用（u-th）/MegeOnalogical技术的使用，即来自20个小，中和大型冲击结构的撞击材料的单个U-和Th-bearening晶体（例如锆石和磷灰石）。 放射性子产品（4HE）的独特特性，即其低闭合温度和高扩散率，使（U-th）/HE技术非常适合与短暂但非常激烈的，非常激烈的，非常激烈的，热和冲击的变态相关的发作撞击结构的形成。 该项目涉及来自8个国家和13个科学机构的国家和国际科学家团队，他们将提供影响结构样本和专业知识来检验这一假设。