Constraining Mantle Rheology at Lithospheric Conditions by Modeling Seamount Induced Deformation and Gravity Anomalies

固体地球的表层被称为岩石圈，平均厚度约100公里，包括地壳和地幔成分。岩石圈相对较冷(即温度低于~1200摄氏度)，在应力作用下以脆性和塑性两种方式变形。岩石圈条件下(即温度低于1200℃)的地幔流变学定量描述了岩石圈在应力作用下的变形，对于理解长期构造变形、造山、火山作用、岩石圈减薄和板块构造具有重要意义。大多数关于地幔岩石圈流变学的研究采用实验室方法，在实验室环境下调查岩石样品或样品对外加应力的响应。尽管实验室研究提供了许多关于岩石圈流变学的重要见解，但将其直接应用于岩石圈变形过程的研究仍然具有挑战性。该项目寻求通过直接模拟与板块内部和俯冲带的海山和洋岛负载有关的表面和莫霍面偏转以及重力异常来限制岩石圈的流变性。海山和海洋岛屿是由于火山喷发在短期(约100万年或更短的时间)内在大洋岩石圈上形成的。它们在大洋岩石圈引起了显著的变形，这在沉积层的变形和重力异常中都可以观察到。因此，海山和海洋岛屿(如夏威夷)对岩石圈的加载可被视为研究岩石圈对应力或加载的响应的天然实验室。这个项目试图解决以下问题：1)板块内部和俯冲带的岩石圈强度(应力)和流变学是什么？2)岩石圈粘度如何随温度变化(即活化能)？3)模拟野外观测得出的地幔流变性与最近实验室研究得出的一致吗？4)俯冲过程，如俯冲带海山所看到的，俯冲过程的流变学效应是什么？拟议的两年项目的具体任务包括：1)建立具有实际流变性的二维和三维有限元粘弹性加载模型，包括粘弹性、非线性蠕变和摩擦(即拜尔利定律)流变学；2)使用最新汇编的约80个海山和海洋岛屿的弹性板厚度、板块年龄、加载年龄和大小的汇编，以约束包括激活能在内的岩石圈条件下的地幔流变性；3)使用地震成像的地壳偏转数据、载荷和岩石圈年龄、选定的板内海洋岛屿(夏威夷、留尼汪岛、加那利、佛得角、以及俯冲带海山(Kermadec海沟附近的Louisville Ridge海山和日本海沟中的Daiichi-Kashima海山)，以进一步约束不同构造背景下的流变性。地球物理学课程。

The surface layer of the solid Earth is called lithosphere that is on average about 100 km thick and includes the crust and mantle components. The lithosphere is relatively cold (i.e., temperature less than ~1200 C) and deforms in both brittle and plastic fashions under stresses. Mantle rheology at lithospheric conditions (i.e., temperature less than 1200 C) describes quantitatively the lithospheric deformation under stress, and is important for understanding long-term tectonic deformation, mountain building, volcanism, lithospheric thinning, and plate tectonics. Most studies on mantle lithospheric rheology employ a laboratory approach and investigate the response of rock samples or specimen to applied stress in laboratory settings. Although laboratory studies have provided many important insights on lithospheric rheology, it remains challenging to directly apply them in studies of lithospheric deformation processes. This project seeks to constrain lithospheric rheology by directly modeling observations of surface and Moho deflections and gravity anomalies associated with seamount and oceanic island loads at plate interiors and in subduction zones. Seamounts and oceanic islands are formed on oceanic lithosphere due to volcanic eruptions on a short time scale (~ 1 million years or less). They cause significant deformation on oceanic lithosphere that can be observed in deformation of sedimentary layers and gravity anomalies. The loading of seamount and oceanic islands (e.g., Hawaii) on lithosphere can therefore be viewed as a natural laboratory to study the lithospheric response to stress or loading. This project seeks to address the following questions: 1) What is the lithospheric strength (stress) and rheology at plate interiors and in subduction zones? 2) How does lithospheric viscosity vary with temperature (i.e., activation energy)? 3) Is the mantle rheology inferred from modeling field-based observations consistent with that inferred from recent laboratory studies? 4) What are the rheological effects of subduction processes such as faulting, bending and hydration, as seen by subduction zone seamounts? The specific tasks for the proposed two-year project include: 1) to formulate 2- and 3-D finite element viscoelastic loading models with realistic rheologies including viscoelastic, nonlinear creep, and frictional (i.e., Byerlee's law) rheology, 2) to use recent compilations of elastic plate thickness, plate age, load age and size for ~80 seamounts and oceanic islands to constrain mantle rheology at lithospheric conditions including the activation energy, 3) to use seismically imaged deflected crust data, load and lithospheric ages, gravity data for selected intraplate oceanic islands (Hawaii, La Reunion, Canary, Cape Verde, and Marquesas) and subduction zone seamounts (the Louisville Ridge seamount near the Kermadec trench and the Daiichi-Kashima seamount in the Japan Trench) in 3-D loading models to further constrain the rheology in different tectonic settings.This project is supported by the Geophysics and Marine Geology & Geophysics Programs.