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

通过模拟海山引起的变形和重力异常来约束岩石圈条件下的地幔流变

• 批准号: 1114168
• 负责人: Shijie Zhong
• 金额: $ 19.66万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114168&HistoricalAwards=false
• 关键词: Constraining; Mantle; Rheology; Lithospheric; Conditions

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.

固体地球的表层称为岩石圈，平均厚度约 100 公里，包括地壳和地幔成分。岩石圈相对较冷（即温度低于约 1200 C），在应力作用下会发生脆性和塑性变形。岩石圈条件下（即温度低于1200℃）地幔流变学定量描述了应力作用下岩石圈的变形，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。大多数地幔岩石圈流变学研究都采用实验室方法，研究岩石样本或标本对实验室环境中施加的应力的响应。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，但将它们直接应用于岩石圈变形过程的研究仍然具有挑战性。该项目旨在通过直接模拟地表和莫霍面偏转以及与板块内部和俯冲带的海山和海洋岛屿载荷相关的重力异常的观测结果来约束岩石圈流变学。海山和海洋岛屿是由于短时间尺度（约一百万年或更短）的火山喷发而在海洋岩石圈上形成的。它们引起海洋岩石圈的显着变形，可以在沉积层变形和重力异常中观察到。因此，岩石圈上的海山和大洋岛屿（例如夏威夷）的载荷可以被视为研究岩石圈对应力或载荷的响应的天然实验室。该项目旨在解决以下问题： 1）板块内部和俯冲带的岩石圈强度（应力）和流变性是多少？ 2）岩石圈粘度如何随温度变化（即活化能）？ 3）根据实地观测模拟推断的地幔流变学与最近实验室研究推断的一致吗？ 4）俯冲带海山所看到的俯冲过程（例如断层、弯曲和水化）的流变效应是什么？ 拟议的两年项目的具体任务包括：1）制定具有真实流变学的 2 维和 3 维有限元粘弹性载荷模型，包括粘弹性、非线性蠕变和摩擦（即拜尔利定律）流变学，2）使用最近对约 80 个海山和海洋岛屿的弹性板块厚度、板块年龄、载荷年龄和尺寸进行了汇编，以限制岩石圈条件下的地幔流变学，包括激活能，3) 使用地震成像偏转地壳数据、载荷和岩石圈年龄、选定板内海洋岛屿（夏威夷、留尼旺岛、加那利、佛得角和马克萨斯）和俯冲带海山（靠近大西洋的路易斯维尔海岭海山）的重力数据克马德克海沟和日本海沟的第一鹿岛海山）在 3D 加载模型中进一步约束不同构造的流变性设置。该项目由地球物理学和海洋地质与地球物理学计划支持。