A new hypothesis for the initiation of plate tectonics on Earth: Feedback between subduction and continental crust growth

这一提议研究了板块构造是如何在地球历史上开始和演变的。板块构造是指地球表层被分解成相互相对运动的刚性板块。板块构造是地球上最重要的过程之一，因为它是造成大多数地震、火山和地表地貌特征（如山脉和地质）的原因。然而，板块构造在地球历史上何时以及如何开始并不为人所知。该项目将研究大陆的形成在引发地表板块运动中所起的作用。大陆是地壳中化学成分不同的区域，比相应的海洋盆地更厚、更高。通过将理论模型与对地球上一些最古老岩石的观察相结合，这项被提议的工作将检验一个关于板块构造是如何开始的新理论，从而促进我们对这一根本重要过程的理解。这个建议促进了科学的进步，符合国家利益。特别是，该提案将通过支持一名研究生研究员三年和一名本科生实习一个夏天来促进地球科学的教育和多样性。研究生将获得地球物理学和跨学科地球系统科学方面的宝贵培训和研究经验，适用于学术界或工业界的职业生涯。该本科生将通过宾夕法尼亚州立大学的暑期研究机会项目（Summer Research Opportunities Program）接受培训，该项目面向来自科学领域代表性不足的群体或背景的学生。因此，接待实习生不仅将为本科生提供最前沿的地球科学研究经验，还将有助于建立地球科学的多样性。在这个提议中要验证的假设是，大陆地壳生长和俯冲之间的反馈导致了整个地球上现代板块构造的逐步开始。该提案将使用地幔对流的数值模型和包含大陆地壳生长的地球热演化模型来验证这一假设。提出的工作将回答三个主要的科学问题：1)大陆是否加强了岩石圈的弱化，从而导致弱板块边界的形成和其边缘现代式的俯冲，以及由于大陆形成而开始俯冲的时间尺度是否与地质观测相符？2)大陆对岩石圈减弱的影响是局部的还是全球的？大陆的大小如何改变这种影响的长度尺度？3)大陆的存在是否由于俯冲增强而导致长英质岩浆活动速率的提高？地壳生长和俯冲之间的反馈是否如地质观测所表明的那样，在1 ~ 1 Gyr的时间尺度上导致全球向板块构造过渡？对于每个科学问题，将进行一套详细、彻底的建模工作，以限制所有关键模型参数对结果的影响，并允许结果的稳健性得到充分测试。板块构造的开始是地球历史上的一个开创性事件，从根本上重塑了地球的热、化学和地质演化。因此，提出的工作将大大提高我们对地球历史上可能最重要的地球物理事件的理解。通过提供一个可以放置地质观测的大规模地球动力学框架，结果将对解释太古代地质学和地球化学具有直接意义。板块构造也从根本上改变了地表和内部挥发物的循环，因此在地球的长期演化中起着重要作用。年代的气氛。因此，这一提议的结果将直接关系到地球大气层以及对生命至关重要的地表环境如何随着时间的推移而演变。

This proposal studies how plate tectonics, the concept that Earth's surface layer is broken into rigid plates that move with respect to one another, started and evolved over Earth's history. Plate tectonics is one of the most important processes on Earth, as it is responsible for most earthquakes, volcanoes, and surface landscape features such as mountain ranges and geology. However, when and how plate tectonics begin during Earth's history is not well known. The project will study the role that the formation of continents, chemically distinct regions of Earth's crust that are thicker and sit higher than the corresponding ocean basins, play in initiating surface plate motion. By combining theoretical models with observations of some of Earth's oldest rocks, the proposed work will test a new theory for how plate tectonics started, and thus advance our understanding of this fundamentally important process. The proposal serves the national interest by promoting the progress of science. In particular, the proposal will advance education and diversity in the geosciences, by supporting a graduate student researcher for three years and an undergraduate student intern for one summer. The graduate student will receive valuable training and research experience in geophysics and interdisciplinary Earth systems science, applicable to careers in academia or industry. The undergraduate will be hosted through the Summer Research Opportunities Program at Penn State University, which is geared towards students from groups or backgrounds that are underrepresented in the sciences. As a result, hosting the intern will not only provide an undergraduate student with experience in cutting edge Earth science research, but will also contribute to building diversity in the Earth sciences.The hypothesis to be tested in this proposal is that a feedback between continental crust growth and subduction leads to the progressive initiation of modern-style plate tectonics across the planet. The proposal will use numerical models of mantle convection and thermal evolution models of the Earth incorporating continental crust growth to test this hypothesis. The proposed work will answer three main science questions: 1) Does a continent enhance lithospheric weakening, and thus induce formation of a weak plate boundary and modern-style subduction at its margin, and is the timescale for subduction to begin as a result of continent formation consistent with geologic observations? 2) Is the effect of a continent on lithospheric weakening felt locally or globally, and how does continent size change the length-scale over which this effect is felt? 3) Does the presence of a continent lead to higher rates of felsic magmatism due to enhanced subduction, and does the feedback between crustal growth and subduction cause a global transition to plate tectonics over a ~ 1 Gyr timescale, as indicated by geological observations? For each science question a detailed, thorough set of modeling work will be carried out that constrains the effect of all key model parameters on the results, and allows the robustness of the results to be fully tested. The initiation of plate tectonics was a seminal event in Earth's history, fundamentally reshaping its thermal, chemical, and geologic evolution. Thus the proposed work will significantly advance our understanding of perhaps the most important geophysical event in Earth's history. The results will have direct implications for interpreting Archean geology and geochemistry, by providing a large-scale geodynamic framework that geological observations can be placed in. Plate tectonics also fundamentally alters cycling of volatiles between the surface and interior, and thus plays a role in the long-term evolution of Earth?s atmosphere. The results of this proposal will thus have direct bearing on how Earth's atmosphere, and therefore the surface environment so crucial for life, has evolved over time.