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.

板块构造学是一种理论，即地球最外层，即地壳，被分成不同的板块，这些板块穿过地幔(地壳正下方的层)移动。这种板块运动导致了地球上大多数火山和地震，理论上被认为是对地球上生命形成的重要控制。然而，关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：板块构造是何时、为什么以及如何开始的？为了了解这些变化，我们将使用一种名为锆石的矿物。锆石之所以重要，是因为它具有物理和化学弹性，它形成的环境种类繁多，而且它提供了丰富的化学信息。它也是40.1亿年前(GA)之前唯一的岩石遗迹。以前的研究发现证据表明，锆石的源岩在38亿Ga和大约3.6Ga之间发生了变化(Bauer等人。2020)。这种变化被认为表明地球上板块构造过程的变化。然而，需要更多的信息来了解板块构造在地球历史的头10亿年是否活跃，包括关于地表水或近地表水的范围和岩石类型变化的信息。通过对怀俄明省和辛格洪克拉通两个未调查地点的Hadean(4.01Ga)和Archean(2.5Ga~4.01Ga)锆石的微量和稀土元素、年龄、氧同位素、硅同位素和矿物包裹体的高分辨率空间分析，将对与地球表面和内部有关的约10亿年的历史进行解释。这些研究将探索这些时期地球上液态水的空间和时间范围、构造转变和地壳成分，并对这些早期亿万年的地壳过程提供进一步的限制。该项目将包括对哈佛大学本科生的指导，为高中生提供的研究经验，以及通过博物馆、哈佛大学和其他社区项目的活动延伸到大波士顿社区。在这个项目中，将对来自怀俄明省和辛格洪姆克拉通的哈甸和太古宙锆石进行分析，以扩大人们对早期地球的了解。具体地说，将研究三个主题：1)支持和反对早期地球历史不同时期现代式俯冲的证据，2)早期地球表面或近地表水的时空分布，以及3)早期地球上岩石类型的分布。对锆石年代的现场分析将包括Si-O耦合同位素的测量、微量元素和包裹体研究。通过这个项目，原本旨在了解背景锆石的技术，或那些具有非常著名的地质来源的技术，将应用于地球最早历史上的样品。在这方面，将面临与这些技术的可伸缩性相关的假设。例如，可以假设过去几亿年来统治地球的物理过程，如板块构造，在40亿多年前就有效了吗？如果它们不是，那么早期地球上运行的过程是什么？这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。