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

一个构造板块下沉到另一个板块之下进入地幔称为俯冲。它是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，俯冲是如何开始的，以及在俯冲开始（SI）期间构造板块如何改变其形状仍然不清楚。主要的驱动力是俯冲板块的负浮力和横向推动构造板块的外力。主要的阻力包括俯冲板块的弯曲阻力、俯冲板块和覆盖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强烈地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，这些材料的性能往往被假定为统一的数值模拟SI，尽管它们的压力，温度，应力和成分的依赖。三种机械性能中的哪一种（即，粘性、弹性和塑性）取决于它们的相对值来控制俯冲板块的弯曲。利用数值模型，本研究的目的是更好地了解如何弯曲行为的俯冲板的变化与三个力学性能。该项目为一名早期职业女性教师和一名博士后研究员提供支持，将开发一套通用的二维和三维动力俯冲模型，包括粘塑性和粘弹塑性流变学，以量化弹性对俯冲板片下倾和侧向弯曲的影响。这些模型将纳入一个复合的粘性流变，占位错蠕变和扩散蠕变，模型与粘弹塑性流变纳入压力和温度依赖性剪切模量，使用热力学代码Perple_X。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启动俯冲，以及（2）弹性是否是抵抗或促进下倾和侧向弯曲/不弯曲的流变学成分？还将进行俯冲参数对板块演化影响的系统试验，以解决这些问题。此外，还将为选定的真实的俯冲系统（包括马里亚纳群岛、汤加和普伊塞古尔）建立二维和三维模型，并将结果与构造历史和当前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，而且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，这些信息将有助于解释地球物理和地球化学观测。研究结果将在PI的研究网站和YouTube上发布的科学视频以及会议演示和同行评审的期刊文章中进行总结。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估而被认为值得支持。

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.