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

该提案研究了板块构造，即地球表层被分解为相对于彼此移动的刚性板块的概念，如何在地球历史上开始和演变。板块构造是地球上最重要的过程之一，因为它是大多数地震，火山和地表景观特征，如山脉和地质的原因。然而，在地球历史上，板块构造开始的时间和方式并不为人所知。该项目将研究大陆的形成在启动板块运动方面的作用，大陆是地壳中化学性质不同的区域，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的岩石的观察相结合，这项工作将测试板块构造如何开始的新理论，从而推进我们对这一根本性重要过程的理解。这项建议通过促进科学进步来服务于国家利益。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生一个夏天来促进地球科学的教育和多样性。研究生将获得宝贵的培训和研究经验，在地球物理学和跨学科的地球系统科学，适用于学术界或工业界的职业生涯。本科生将通过宾夕法尼亚州立大学的夏季研究机会计划进行托管，该计划面向来自科学领域代表性不足的群体或背景的学生。因此，接待实习生不仅可以为本科生提供前沿地球科学研究的经验，还将有助于建立地球科学的多样性。本提案中要验证的假设是，大陆地壳生长和俯冲之间的反馈导致全球现代板块构造的逐步启动。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检验这一假设。拟议的工作将回答三个主要的科学问题：1）大陆是否增强了岩石圈的弱化，从而导致在其边缘形成弱板块边界和现代风格的俯冲，以及作为大陆形成的结果，俯冲开始的时间尺度是否与地质观测一致？2)大陆对岩石圈弱化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)是否存在一个大陆导致更高的速度长英质岩浆作用，由于加强俯冲，地壳生长和俯冲之间的反馈，导致全球过渡到板块构造在一个~ 1 Gyr的时间尺度，如地质观测所示？对于每个科学问题，将进行详细，全面的建模工作，限制所有关键模型参数对结果的影响，并允许充分测试结果的鲁棒性。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，拟议中的工作将大大推进我们对地球历史上最重要的地球物理事件的理解。这些结果将直接影响解释太古代地质和地球化学，通过提供一个大规模的地球动力学框架，地质观测可以放置。板块构造也从根本上改变了挥发物在地表和内部之间的循环，从而在地球的长期演化中发挥了作用？的大气层。因此，这一提议的结果将直接影响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.