Untangling the Roles of Viscous, Elastic, and Plastic Deformation in Slab Bending

阐明粘性变形、弹性变形和塑性变形在板坯弯曲中的作用

• 批准号: 2054597
• 负责人: Ikuko Wada
• 金额: $ 16.07万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2054597&HistoricalAwards=false
• 关键词: Untangling; Roles; Viscous; Elastic; Plastic

Sinking of a tectonic plate beneath another plate into the mantle is called subduction. It is a fundamental process that controls the evolution of Earth and holds a key to understanding important processes, such as earthquakes, volcanism, and mantle convection. However, how subduction initiates and how the tectonic plate changes its shape during subduction initiation (SI) are still unclear. The key driving forces are the negative buoyancy of the subducting plate and external forces that push the tectonic plates laterally. The key resisting forces include bending resistance of the subducting plate, frictional resistance between the subducting and overriding plates, and viscous resistance that is exerted by the surrounding mantle on the subducting plate. The details of SI and how the subducting plate bends depend strongly on the balance between these forces and also on the strength of the subducting slab, which has been defined by some combination of viscosity, elasticity, and plasticity of Earth materials. Further, these material prosperities are often assumed to be uniform in numerical simulations of SI despite their dependence on pressure, temperature, stress, and composition. Which of the three mechanical properties (i.e., viscosity, elasticity, and plasticity) controls the bending of the subducting plate depends on their relative values. Using numerical models, this study aims to better understand how the bending behavior of the subducting plate changes with the three mechanical properties. The project provides support for an early-career female faculty member and a postdoctoral scholar.A suite of generic 2-D and 3-D dynamic subduction models with a visco-plastic and a visco-elasto-plastic rheology will be developed to quantify the effect of elasticity on down-dip and lateral bending of the subducting slab. These models will incorporate a composite viscous rheology that accounts for both dislocation creep and diffusion creep, and models with the visco-elasto-plastic rheology incorporates pressure- and temperature-dependent shear modulus, using the thermodynamic code Perple_X. The models are used to address two key questions: (1) Can the negative buoyancy of the oceanic lithosphere be sufficient to overcome the elastic bending resistance and to initiate subduction, and (2) Is elasticity a rheological component that resists or facilitates down-dip and lateral bending/unbending? Systematic tests on the effect of subduction parameters on the slab evolution will also be performed to address these questions. Further, 2-D and 3-D models will be developed for selected real subduction systems, including Marianas, Tonga, and Puysegur, and the results will be compared with the tectonic history and the current slab geometry. The numerical models to be developed will provide not only the geometrical evolution of the slab but also the temperature and mantle flow fields of subduction systems over a range of parameters, and the information will be useful for the interpretations of geophysical and geochemical observations. The results will be summarized in scientific videos to be distributed through the PI’s research website and YouTube as well as in conference presentations and peer-reviewed journal articles.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.

一个构造板块在另一个板块下方下沉到地幔中的过程称为俯冲。这是一个控制地球演化的基本过程，也是理解地震、火山活动和地幔对流等重要过程的关键。然而，俯冲如何开始以及构造板块在俯冲开始(SI)期间如何改变其形状仍然不清楚。主要驱动力是俯冲板块的负浮力和推动构造板块横向运动的外力。主要的阻力包括俯冲板块的弯曲阻力、俯冲板块与俯冲板块之间的摩擦阻力以及周围地幔对俯冲板块施加的粘性阻力。SI的细节和俯冲板块如何弯曲在很大程度上取决于这些力之间的平衡，也取决于俯冲板块的强度，这是由地球材料的粘性、弹性和塑性的某种组合定义的。此外，在SI的数值模拟中，通常假定这些材料的丰度是一致的，尽管它们依赖于压力、温度、应力和成分。三种力学性质(即粘性、弹性和塑性)中的哪一种控制俯冲板块的弯曲取决于它们的相对值。利用数值模型，本研究旨在更好地了解俯冲板块的弯曲行为如何随三种力学性质的变化而变化。该项目将为职业生涯早期的女教员和博士后学者提供支持。将开发一套具有粘塑性和粘弹塑性流变学的通用二维和三维动态俯冲模型，以量化弹性对俯冲板下倾和横向弯曲的影响。这些模型将包括考虑位错蠕变和扩散蠕变的复合粘性流变学，以及使用热力学代码Perple_X的粘弹塑性流变学模型包含与压力和温度相关的剪切模数。这些模型用于解决两个关键问题：(1)海洋岩石圈的负浮力是否足以克服弹性弯曲阻力并引发俯冲；(2)弹性是抵抗或促进下倾和横向弯曲/伸展的流变学成分吗？为了解决这些问题，还将进行关于俯冲参数对板块演化影响的系统测试。此外，将为选定的真实俯冲系统开发2-D和3-D模型，包括马里亚纳群岛、汤加和普伊塞格尔，并将结果与构造历史和当前的板块几何形状进行比较。将要开发的数值模型不仅将提供板块的几何演化，还将提供俯冲系统在一系列参数范围内的温度和地幔流场，这些信息将有助于地球物理和地球化学观测的解释。结果将在科学视频中总结，并通过PI的研究网站和YouTube分发，以及在会议演示文稿和同行评议的期刊文章中发布。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Effects of Elasticity on Subduction Initiation: Insight From 2‐D Thermomechanical Models

• DOI: 10.1029/2022jb024400
• 发表时间: 2022-10
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Xin Zhou;I. Wada