EAR-PF: A high-resolution 142Nd/144Nd record of mantle-derived rocks to constrain mantle stirring rate and tectonic regimes

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。Eugenia Hyung博士被授予EAR博士后奖学金，在哈佛大学和内华达大学拉斯维加斯分校开展研究和教育计划。亨博士将利用对地球深处和时间深处岩石组成的高精度测量，更好地了解地球的历史。板块构造——大型岩石板块在地球表面的运动——影响着地球演化的命运。通过板块构造，地球表面是由下面的地幔形成的，影响了造山运动，形成了海底，并产生了许多大地震和火山爆发。然而，板块构造的起源和历史还没有被很好地理解。了解地幔是如何形成的，将有助于回答这些问题。由于在整个地质历史的关键时间间隔中缺少高精度的化学数据，所以关于地幔如何以及以何种速度随时间均匀化的精确限制仍然存在疑问。该项目旨在通过从数十亿年前的岩石中获取高精度数据来确定地幔的搅拌时间，从而解决这些问题。这项工作将在Stein B. Jacobsen教授（哈佛大学）和Shichun Huang教授（拉斯维加斯内华达大学）的指导下进行。在进行这项研究的同时，Hyung博士将为研究生和本科生提供指导，参与开发教学方法和课程，并参与推广活动，以促进在当前问题背景下对地球的理解和欣赏，以及地球随时间的演变。在短命的146Sm同位素灭绝之后很久，142 /144Nd的变异才出现，这导致了这样一种观点，即地球历史早期的构造模式可能与现在的构造形式有着根本的不同，从而使地球化学的异质性得以保存数十亿年。构造模式（活动盖与停滞盖）被认为对地幔混合的效率和硅酸盐地球的均质化产生影响。通过这个项目，Eugenia Hyung博士的目标是限制地幔的搅拌速率，并推断出发生这种情况的时间框架内的主要构造模式，通过(i)通过对元古代样品进行高精度测量来填补第142 /144Nd同位素记录的空白，（ii）通过建模得出这段时间内地幔的搅拌速率，使用数据作为约束。PI Eugenia Hyung博士非常适合进行拟议的研究，他之前开发了测量142 /144Nd比率的方法，精度非常高，同时具有建模经验。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. Eugenia Hyung has been granted an EAR Postdoctoral Fellowship to carry out research and education plans at Harvard University and University of Nevada Las Vegas. Dr. Hyung will use high precision measurements of the composition of rocks from deep in the Earth and deep in time to better understand Earth’s history. Plate tectonics – the movement of large rocky plates over the surface of the Earth – influences the fate of Earth’s evolution. Through plate tectonics, the surface of the Earth is shaped by the mantle below, influencing mountain building, creating the ocean floor, and generating many major earthquakes and volcanic eruptions. Yet the origin and history of plate tectonics is not well understood. Understanding how the mantle is shaped throughout time, will help to answer these questions. Because high-precision chemical data are missing from key time intervals throughout geologic history, questions remain about precise limits on how and at what rate the mantle becomes homogenous through time. This project aims to address these questions by acquiring high-precision data from rocks that are billions of years old to establish the stirring time of the mantle. The work will be carried out under the mentorship of Professor Stein B. Jacobsen (Harvard University) and Professor Shichun Huang (University of Nevada, Las Vegas). While conducting this research, Dr. Hyung will provide mentorship to both graduate and undergraduate students, be involved in developing teaching methods and courses, and engage in outreach activities that promote understanding and appreciation of the Earth in the context of current issues, as well as its evolution throughout time.The presence of 142Nd/144Nd variability well after the extinction of the short-lived 146Sm isotope has led to the idea that the mode of tectonics early in Earth’s history would have been fundamentally different from the present-day form of tectonics to have enabled the preservation of geochemical heterogeneity over billions of years. The mode of tectonics (mobile vs. stagnant lid) is thought to exert influence on the efficiency of mantle mixing, and homogenization of the silicate Earth. Through this project, PI Dr. Eugenia Hyung aims to constrain the stirring rate of the Earth’s mantle and to deduce the dominant mode of tectonics in the time frame in which this occurs, by (i) filling the gap in the 142Nd/144Nd isotope record by performing high-precision measurements on Proterozoic samples and (ii) derive the stirring rate of the mantle during this time period through modeling, using the data as constraints. PI Dr. Eugenia Hyung is well-positioned to undertake the proposed study, having previously developed the methods in measuring 142Nd/144Nd ratios at a very high degree of precision while having experience in modeling.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.