Constraining multi-scale interactions between slabs and mantle flow within Western Pacific subduction zones

俯冲带是一个构造板块下降到另一个构造板块之下的地方，它形成了地球上一些最引人注目的山脉，也是一些最致命的地震和火山的原因。在下面的地幔中，下降的板块被称为“板块”，它被更热的物质包围，这些物质在地质时期表现为流体。板块周围地幔流动的模式和速度决定了作用在板块和上覆板块上的力的方向和大小。这些力量在驱动板块变形，包括造山运动和地震中起着重要作用，但它们无法直接观测到。必须使用复杂的数学模型来估计它们。在这个项目中，霍尔特和他的团队将开发这样的模型，并运行几组计算来研究地幔流及其对西太平洋地区板块和板块的影响。之所以选择这个区域，是因为有大量的数据可以用来测试模型计算，而且因为板和板块的几何形状很复杂（因此很有趣）。将具有这种复杂性的模型集成到全球尺度的地幔流模型中提出了一个巨大的技术挑战，霍尔特已经部分满足了这一挑战。他的团队的新模型将首先解决地幔流可能与旧的简化模型给出的估计有多大差异。经过调整，使之与西太平洋的地质和地球物理数据相一致，这些模型将为这一复杂地区的地幔流动和板块作用力提供新的认识。PI和团队将开发并免费共享软件工具，为其他团队模拟类似复杂的地震多发地区（例如，加勒比和东南亚）。该项目将支持一名研究生和一名早期职业教授。模型和输出将用于教授迈阿密大学地球动力学学生模型可视化和数据分析。该研究项目的总体目标是为地幔和岩石圈板块之间的相互作用建立一个力学框架，重点是几何复杂的西太平洋。该框架将通过使用一套全球俯冲模型来预测主要西太平洋板块附近的地幔流状态和相关力量（例如，千岛-日本、琉球-南海和伊豆-小笠原-马里亚纳）。在该团队编制了一个对地幔动力学敏感的西太平洋观测数据库后，将运行包含高分辨率西太平洋板块和弱板块边界的全球数值模型，以量化与这些观测结果一致的地幔流和粘度场。该团队还将使用一套有针对性的数值测试来研究流场和相关力如何受到全球尺度流动和地幔流局部化（由于幂律粘性流变学）的影响。 三个相互关联的问题有关的岩石圈地幔流动的相互作用将得到解决。在区域一级：菲律宾海板块（PSP）下的地幔外流是否发生并产生了决定西太平洋俯冲观测的力量？这种通过平板之间狭窄间隙发生的流出，是否由于幂律蠕变而需要流动局部化？在全球范围内：大规模地幔流施加的力是否强烈影响西太平洋板块（例如，它们是否产生了日本板块的非常浅的倾角）？在解决这些问题，这项研究将提供可转移的洞察复杂的板几何形状和全球规模的地幔流俯冲带mechanics.This奖项的相对贡献反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Subduction zones, where one tectonic plate descends beneath another, are responsible for forming some of the Earth's most dramatic mountain ranges - and for some of its deadliest earthquakes and volcanoes. In the underlying mantle, where the descending plate is referred to as a “slab”, it is surrounded by hotter material which behaves as a fluid over geological time. The pattern and speed of mantle flow around the slab governs directions and magnitudes of forces acting on it and on the overlying plates. These forces play an important role in driving plate deformation, including mountain building and earthquakes, but they cannot be observed directly. They must be estimated, using sophisticated mathematical models. In this project, Holt and his team will develop such models and run several sets of calculations to investigate mantle flow and its effect on slabs and plates in the Western Pacific region. This region was chosen because there is abundant data that can be used to test the model calculations, and because the geometry of slabs and plates is complex (and hence interesting). Integrating a model with this complexity into a global-scale mantle flow model presents an immense technical challenge which has already been partially met by Holt. His group's new models will first address how much mantle flow may differ from estimates given by older, simplified models. After they have been adjusted to be consistent with geological and geophysical data from the Western Pacific, the models will shed new light on mantle flow and forces on plates in this complex region. The PI and team will develop and freely share software tools, opening the door for other groups to model similarly complex, earthquake-prone regions (e.g., the Caribbean and Southeast Asia). This project will support a graduate student and an early-career professor. The models and outputs will be used for teaching model visualization and data analysis to Geodynamics students at the University of Miami. The overarching goal of this research project is developing a mechanical framework for interactions between the mantle and lithospheric plates, with a focus on the geometrically complex Western Pacific. This framework will be developed by using a suite of global subduction models to predict the mantle flow regime and associated forces in the vicinity of the main Western Pacific slabs (e.g., Kuril-Japan, Ryukyu-Nankai, and Izu-Bonin-Mariana). After the team compiles a database of Western Pacific observables sensitive to mantle dynamics, global numerical models incorporating highly resolved Western Pacific slabs and weak plate boundaries will be run to quantify the mantle flow and viscosity fields consistent with these observations. The team will also use a suite of targeted numerical tests to examine how the flow-field and associated forces are impacted by both global-scale flow and mantle flow localization (due to a power-law viscous rheology). Three inter-linked questions related to lithosphere-mantle flow interactions will be addressed. At a regional scale: Does mantle out-flow from beneath the Philippine Sea Plate (PSP) occur and produce forces that dictate Western Pacific subduction observables? Does this out-flow, which occurs through narrow gaps between slabs, require flow localization due to power-law creep? At a global scale: Do forces imposed by large-scale mantle flow strongly impact the Western Pacific slabs (e.g., do they produce the very shallow dip of the Japan slab)? In addressing these questions, this study will provide transferrable insight on the relative contributions of complex slab geometries and global-scale mantle flow to subduction zone mechanics.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.