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.

数十亿年来，小行星和彗星一直轰炸着太阳系的行星。 在地球上，活跃的地质过程已经摧毁或隐藏了大约 90% 的撞击坑，迄今为止，仅发现了 176 个撞击结构。 近年来，科学界已经认识到撞击事件对地球地质和生物历史的重要性，其中包括与大型希克苏鲁伯撞击坑有关的 6500 万年前的恐龙大灭绝事件。 因此，确定这些已知撞击事件的准确年龄对于我们了解地球历史至关重要。 不幸的是，由于传统测年技术的应用并不总是成功，大约 80% 的已识别陆地撞击结构的年龄未知或仅大致已知。 该项目代表了一种新的测年技术的应用，该技术在初步研究中显示出极大的希望，可以提高我们对地球外星撞击历史的理解。 具体来说，该项目将涉及使用 (U-Th)/He 地质年代学技术来对来自 20 个小型、中型和大型冲击结构的冲击材料中的单个含 U 和 Th 晶体（例如锆石和磷灰石）进行年代测定。 放射成因子产物 (4He) 的独特性质，即其低闭合温度和高扩散率，使得 (U-Th)/He 技术成为测定与撞击结构形成相关的短暂但非常强烈的热和冲击变质事件的理想选择。 该项目涉及来自 8 个国家和 13 个科研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。