4-D Geodynamic Modeling With Data Assimilation: Origin Of Intra-Plate Volcanism In The Pacific Northwest

大陆火山活动是地球上主要的自然灾害。了解火山作用的形成机制是科学界非常感兴趣的问题。本文旨在解决目前在地表火山特征解释、地幔地震图像解释、系统整体演化等方面存在的困惑。由于其多学科性质，这项拟议的研究将具有广泛的变革性。例如，了解过去的地幔演化将有助于确定各种地幔地震结构的构造起源，这是地球物理学的一个重要目标；更好的约束地幔热结构将为解释与火山活动有关的地球化学数据提供新的背景；将板块运动历史与地幔动力学联系起来，将为地表构造变形提供新的认识，为地质记录的解释提供新的视角。最重要的是，像这里提出的长期地球演化模型将提供一个框架，在不同的地球科学研究领域之间建立物理联系，并将发生在不同时空尺度上的动态过程联系起来。此外，建议的研究将为通识教育制作优秀的讲座材料。PI计划参与通过在线教学提供K-12课程的iRISE项目等外展活动。太平洋西北板块内火山省的起源，包括中新世中期的斯廷斯-哥伦比亚河洪水玄武岩以及随后的黄石和纽伯里热点痕迹，在经过几十年的研究后仍然存在激烈的争论。一种流行的假设是，这个火山省是由起源于核幔边界地区的地幔柱形成的。另一种说法是，许多模型认为它的起源很浅，不涉及地幔柱。然而，这些早期的概念模型大多没有考虑到地幔的观测约束，这些约束是最近在USArray的帮助下才得以实现的。从这些数据中产生的断层扫描反演揭示了美国西部地幔结构的前所未有的细节，这反过来又提供了相应的地幔动力学及其随时间演变的重要信息。这些地震图像也为太平洋西北火山历史的起源提供了新的视角。本项目将利用Blue Waters超级计算机模拟美国西部中生代-新生代法拉龙板块俯冲史背景下的次岩石圈动力学演化，定量评价太平洋西北火山省的起源。该项目首先基于近期地震层析成像，利用正演和伴随方法计算中新世以来的详细地幔流，然后探讨对观测到的缓慢地震异常和地表火山活动产生的三个假设：1)俯冲环境下的地幔柱，2)板块生成的地幔上涌，3)热海洋软流圈的夹带和侵入。具有真实初始和边界条件的高分辨率地球动力学模型将用于计算地幔流动和检验假设。

Continental volcanism represents a major natural hazard on Earth. Understanding the formation mechanism of volcanism is of high interest to the scientific community. The proposed work aims to clear out the existing confusions on the interpretation of surface volcanic features, mantle seismic images, and the systems overall evolution with time. This proposed research will be broadly transformative due to its multidisciplinary nature. For example, understanding past mantle evolution will help identify the tectonic origin of variousmantle seismic structures, an important goal of geophysics; a better constrained mantle thermal structure will provide a new context for explaining geochemistry data associated with volcanism; linking plate motion history and mantle dynamics will lead to new insights of surface tectonic deformation, which may provide a new perspective for interpreting geological records. Most importantly, long-term Earth evolution models like the one proposed here will provide a framework for establishing physical connections among different fields of geoscience research and linking dynamic processes occurring at different spatial and temporal scales. Additionally, the proposed research will produce excellent lecture materials for general education. The PI plans to participate in outreach activities such as the iRISE program to deliver K-12 lectures through online teaching. Origin of the Pacific Northwest intra-plate volcanic province, including the mid-Miocene Steens-Columbia River flood basalt and subsequent Yellowstone and Newberry hotspot tracks, still remains heavily debated after decades of research. One popular hypothesis is that this volcanic province formed from a mantle plume originating from the core-mantle boundary region. Alternatively, many models argued for a shallow origin, without involving a mantle plume. However, most of these earlier conceptual models did not consider observational constraints from the mantle, which only became available recently with the help of USArray. The tomography inversions generated from these data reveal unprecedented details on the mantle structure of western U.S., which in turn provide important information on the corresponding mantle dynamics and its temporal evolution over time. These seismic images also present a new perspective on the origin of Pacific Northwest volcanic history. The proposed project will use the Blue Waters supercomputer to quantitatively evaluate the origin of the Pacific Northwest volcanic province by simulating the sub-lithosphere dynamic evolution of western United States in the context of Mesozoic-Cenozoic subduction history of the Farallon plate below North America. The PI proposes to, first, calculate the detailed mantle flow since the Miocene using forward and adjoint methods based on recent seismic tomography and then to explore three hypotheses on the generation of observed slow seismic anomalies and surface volcanism including: 1) a mantle plume in a subduction environment, 2) slab-generated mantle upwelling, and 3) entrainment and intrusion of hot oceanic asthenosphere. High-resolution geodynamic models with realistic initial and boundary conditions will be used to calculate mantle flow and test hypotheses.