EAR-PF: Geochemical Evidence for the onset of Plate Tectonics on the Early Earth from the Wyoming Province and Singhbhum Craton

EAR-PF：来自怀俄明州和 Singhbhum 克拉通的早期地球板块构造开始的地球化学证据

• 批准号: 2204595
• 负责人: Heather Kirkpatrick
• 金额: $ 18万
• 依托单位: Kirkpatrick, Heather Margaret
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2204595&HistoricalAwards=false
• 关键词: EAR; PF; Geochemical; Evidence; onset

Plate tectonics is the theory that the Earth’s outermost layer, which is called the crust, is divided into different plates which move across the mantle (the layer directly below the crust). This plate movement causes most volcanos and earthquakes on Earth and is theorized to be an important control on life formation on Earth. However, there is disagreement on when plate tectonics began. This work seeks to answer a crucial question in the earth sciences: When, why, and how did plate tectonics start? To understand these changes, a mineral called zircon will be used. Zircon is important because of its physical and chemical resilience, the wide variety of environments where it forms, and the rich chemical information it provides. It is also the only remnant of rock from before 4.01 billion years ago (Ga). Previous studies found evidence of a change in the source rocks of zircon between 3.8 billion Ga and approximately 3.6 Ga (Bauer et al. 2020). This variation has been argued to indicate a change in plate tectonic processes on Earth. However, more information is needed to understand whether plate tectonics was active during the first ~1 billion years of Earth’s history, including information on the extent of surface or near-surface water and variations in rock types. Through high-resolution spatial analysis of trace and rare earth elements, ages, oxygen isotopes, silicon isotopes, and mineral inclusions of Hadean ( 4.01 Ga) and Archean (2.5 Ga to 4.01 Ga) zircon from two under-investigated sites, the Wyoming Province and the Singhbhum Craton, interpretations of ~1 billion years of history related to Earth’s surface and interior will be made. These investigations will explore the spatial and temporal extent of liquid water on Earth, tectonic transitions, and crustal composition during these periods and provide further constraints on crustal processes during these early eons. This project will include mentorship of undergraduate students at Harvard, research experiences for high school students, and outreach to the greater Boston community through events at museums, Harvard and other community programs. In this project, Hadean and Archean zircons from the Wyoming Province and the Singhbhum Craton will be analyzed in order to expand people’s understanding of early Earth. Specifically, three topics will be investigated: 1) evidence for and against modern-style subduction at different periods in early Earth’s history, 2) the spatial and temporal distribution of surface or near-surface water on early Earth, and 3) the distribution of rock types on early Earth. In-situ analyses of dated zircons will include measurements of Si-O coupled isotopes, trace elements, and inclusion studies. Through this project, techniques originally designed to understand in-context zircons, or those with a very well-known geologic origin, will be applied to samples from Earth’s earliest history. Within this, assumptions related to the scalability of these techniques will be confronted. For example, can it be assumed that the physical processes which have governed Earth over the past few hundred million years, such as plate tectonics, were in effect over 4 billion years ago? If they were not, what processes operated on early Earth?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

板块构造理论认为，地球的最外层（称为地壳）分为不同的板块，这些板块在地幔（地壳正下方的层）上移动，这种板块运动导致地球上大多数火山和地震，其理论依据是：然而，对于板块构造何时开始存在分歧，这项工作试图回答地球科学中的一个关键问题：板块构造何时、为何以及如何开始？锆石的重要性在于其物理和化学弹性、其形成环境的多样性以及其提供的丰富的化学信息，它也是 40.1 亿年前岩石的唯一残留物。之前的研究发现了锆石源岩在 38 亿 Ga 到大约 3.6 Ga 之间变化的证据（Bauer 等人，2020 年）。然而，需要更多信息来了解地球历史的前 10 亿年中板块构造是否活跃，包括地表或近地表水的范围以及岩石类型的变化。对冥古宙 (4.01 Ga) 和太古宙 (2.5 Ga 至 4.01 Ga) 的痕量和稀土元素、年龄、氧同位素、硅同位素和矿物包裹体进行高分辨率空间分析怀俄明州和辛格胡姆克拉通这两个未充分研究的地点的锆石将解释与地球表面和内部有关的约 10 亿年的历史。这些研究将探索地球上液态水的空间和时间范围以及构造。该项目将包括对哈佛大学本科生的指导、对高中生的研究经验以及通过进一步向更大的波士顿社区进行推广。在该项目中，将对来自怀俄明州和 Singhbhum 克拉通的冥宙和太古代锆石进行分析，以扩大人们对早期地球的了解。具体而言，将研究三个主题：1）证据。支持和反对早期地球历史不同时期的现代式俯冲；2）早期地球上地表或近地表水的时空分布；3）早期地球上岩石类型的分布。对定年锆石的分析将包括硅氧耦合同位素、微量元素和包裹体研究的测量，最初设计用于了解背景锆石或具有众所周知地质起源的锆石的技术将被应用。在此过程中，我们将面临与这些技术的可扩展性相关的假设，例如，是否可以假设过去几亿年统治地球的物理过程（例如板块构造）是存在的。 40 亿多年前就已经生效了？如果不是，早期地球上运行着哪些过程？该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。