Cosmogenic Production Near the Air-Rock Interface

气-岩界面附近的宇宙成因生产

• 批准号: 0921295
• 负责人: Kenneth Farley
• 金额: $ 28.52万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0921295&HistoricalAwards=false
• 关键词: Cosmogenic; Production; Near; Air; Rock

Many important Earth science questions can be addressed by determining the time at which specific rock samples became exposed at the Earth's surface. For example, a terminal moraine consists of boulders deposited at the front of a glacier as it melts; hence the surface exposure age of the boulders constrains the timing of glacial retreat. Over the last fifteen years great progress has been made in the development of techniques to measure such ages via the accumulation of rare isotopes produced by interactions in the uppermost ~ 1 meter of Earth's surface between high energy cosmic rays and the atoms in rocks. Accurate "cosmogenic dating" requires that the rate and systematics of isotope production be accurately known. This project will investigate a particularly poorly understood part of these systematics - the processes occurring at the air-rock interface, where cosmic rays transition from one medium (atmosphere) in to a very different one (rock). Nuclear processes at this interface will be investigated through high spatial resolution analyses in the uppermost few cm of rock of several different isotopes produced by cosmic rays, including helium-3 and neon-21. In addition, synthetic mineral targets will be exposed to cosmic ray irradiation at high elevation in the Andes, where the cosmic ray flux is very high. These targets will be retrieved and analyzed at high spatial resolution for the same set of isotopes. The synthetic targets complement the work on natural rocks because they permit a far more controlled environment in terms of chemical composition and exposure history. The ultimate goal of this research is to increase the accuracy and reliability of using cosmogenic isotopes as tools for determining the age of the Earth's surface. This research has widespread application to investigations of many relevant processes such as rates of erosion, timing of fault movements, and in documenting Quaternary climate change.

可以通过确定在地球表面暴露的特定岩石样品的时间来解决许多重要的地球科学问题。例如，末端由沉积在冰川融化的冰川前部的巨石组成。因此，巨石的表面暴露年龄限制了冰川后退的时间。在过去的十五年中，通过在高能宇宙射线和岩石中的原子之间的相互作用产生的稀有同位素和岩石原子之间的相互作用产生的稀有同位素的积累，取得了巨大进展。准确的“宇宙源性约会”要求准确知道同位素生产的速率和系统。该项目将研究这些系统学的一个特别鲜为人知的部分 - 在空气摇滚界面上发生的过程，其中宇宙射线从一种介质（大气）转变为非常不同的（岩石）。该界面处的核过程将通过在宇宙射线（包括氦3和Neon-21）的几种不同同位素的岩石上最高的岩石上的高空间分辨率分析进行研究。 此外，合成矿物靶标将暴露于安第斯山脉高海拔的宇宙射线照射，那里的宇宙射线通量非常高。这些靶标将在高空间分辨率的相同同位素集中检索和分析。合成目标补充了自然岩石的工作，因为它们在化学成分和暴露历史上允许更具控制的环境。这项研究的最终目的是提高使用宇宙基因素同位素作为确定地球表面年龄的工具的准确性和可靠性。这项研究广泛应用于对许多相关过程的研究，例如侵蚀率，断层运动的时间和记录第四纪气候变化。