CAREER: Investigating the Causes and Consequences of Flat-Slab Subduction in Lithosphere Evolution

板块构造如何塑造地球表面地质（如造山、盆地形成、景观演化、火山活动和地震）仍然是地球科学的一个基本问题。这个问题的关键是潜没方式和动力学的不确定变化，潜没是一个寒冷的海洋板块循环进入地球温暖的内部的过程。在这个提案中，PI计划研究平板俯冲的原因和后果（即，下沉的板块在岩石圈下以亚水平的速度移动，然后沉入地幔），这已经被发现对大陆的演化有很大的影响。由于涉及许多复杂性和未知因素，这个问题传统上很难理解。幸运的是，地球物理数据采集和高性能计算的最新进展使得利用各种数据同化技术建立复杂的物理模型来解决这一重要的地球动力学问题成为可能。利用PI之前在构建正、逆数据模型（类似于天气预报的工作方式）方面的经验，研究者将探索南美、北美和东亚的俯冲历史，这些地区发生了多个平板时代，导致太平洋周围独特的地质。该项目的结果不仅有助于更好地了解地球的基本演化，而且有助于更好地了解自然灾害和资源的形成。该项目还旨在加强对研究人员和学生的地球动力学研究的交流和教育。通过设计一个在线互动地球动力学论坛，PI希望将地球动力学研究推广到广泛的地球科学界，并帮助感兴趣的用户学习地球动力学建模。PI计划将这个地球动力学小组发展成为一个进行跨学科合作研究的社区中心。通过多种以研究为基础的翻转课堂活动，PI还旨在建立现代教育文化，重点是为新世纪培养高素质的地球科学家。最后，本课题将支持和培养两名博士生和几名本科生。人们普遍认为，俯冲过程，特别是平板俯冲作用，强烈地影响着大陆的地质演化和地幔动力学。然而，平板俯冲的原因和结果仍然难以捉摸。这主要是由于难以真实地模拟俯冲的复杂行为及其与上覆大陆的相互作用。在本提案中，PI计划通过将先进的面向数据的物理模型与地质和地球物理约束相结合，提高我们对平板俯冲的物理机制和构造后果的理解。在实践中，他将把完善的俯冲建模工具（包括正演和伴随方法）与来自多个学科的数据约束结合起来。这种全面的建模工作将应用于三个不同的地理位置（南美、北美和东亚），这些位置过去发生过或现在仍在进行平坦俯冲，并且可以评估几种不同的板块变平的物理机制（各种浮力特征的俯冲、快速板块运动和来自厚上覆板块的水动力吸力）。这项工作的多学科性质将使其结果与许多其他研究领域高度相关。

How plate tectonics have shaped the Earth's surface geology (such as mountain building, basin formation, landscape evolution, volcanic activities and earthquakes) remains a fundamental question in geosciences. Key to this question is the uncertain variation in the style and dynamics of subduction, a process when cold oceanic plates recycle into the Earth's warm interior. In this proposal, the PI plans to study the causes and consequences of flat-slab subduction (i.e., down-going plates travel sub-horizontally beneath the lithosphere before sinking into the mantle) that has found to be greatly affecting the evolution of continents. This problem has been traditionally difficult to understand due to the many complexities and unknowns involved. Fortunately, the recent progress in geophysical data acquisition and high performance computing make it possible to tackle this important geodynamic problem by building sophisticated physical models using various techniques of data assimilation. Using the PI's previous experience on constructing both forward and inverse data-oriented models (similar to how weather prediction works), the investigator will explore the subduction history in South America, North America and East Asia, where multiple flat-slab epochs have occurred, resulting in the unique geology surrounding the Pacific Ocean. Results from this project will help to better understand not only basic earth evolution but also formation of natural hazards and resources. This project also aims at enhancing communication and education of geodynamic research to both researchers and students. By designing an online interactive geodynamics forum, the PI hopes to promote geodynamic research to the broad Earth science community, and to help interested users to learn geodynamic modeling. The PI plans to develop this geodynamics group into a community hub for doing cross-disciplinary and collaborative research. With multiple research-based flipped-classroom activities, the PI alsoaims to build a modern education culture, with a key focus on nurturing high quality geoscientists for the new century. Finally, this proposal will support and train two PhD students and several undergraduates.It is widely accepted that subduction processes, especially flat-slab subduction, strongly influence the geological evolution of continents and mantle dynamics. However, both the causes and consequences of flat-slab subduction remain elusive. This is largely due to the difficulty to realistically simulate the complex behavior of subduction and its interaction with the overriding continents. In this proposal, the PI plan's to improve our understanding on the physical mechanisms and tectonic consequences of flat-slab subduction by combining advanced data-oriented physical models with geological and geophysical constraints. In practice, he will combine well-established subduction modeling tools (both forward and adjoint methods) with data constraints from multiple disciplines. This comprehensive modeling effort will be applied to three different geographic locations (South America, North America, and East Asia) where flat subduction occurred in the past or is still going on now, and where several different physical mechanisms for slab flattening (subduction of various buoyancy features, fast plate motions, and hydrodynamic suction from the thick overriding plate) could be evaluated. The multidisciplinary nature of this work will make the results highly relevant to many other research fields.