Evolution and dynamics of subduction, plumes and plate motions

俯冲、羽流和板块运动的演化和动力学

• 批准号: 1247022
• 负责人: Michael Gurnis
• 金额: $ 56万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1247022&HistoricalAwards=false
• 关键词: Evolution; dynamics; subduction; plumes; plate

The surface of the earth is in constant motion via a process known as plate tectonics. The surface of the earth is divided into about a dozen tectonic plates whereby one plate moves (at a few inches per year) with respect to other plates along great faults and fault zones. Although these motions seem small, they are responsible for earthquakes, including great earthquakes, mountain building, and the formation of sedimentary basins. Consequently, plate tectonics is simultaneously responsible for both some of the most significant geological hazards as well as the formation of the largest hydrocarbon reservoirs. With this project, we aim to better understand the forces that drive and resist plate motions and thereby obtain a deeper understanding of the forces that drive natural hazards and natural resources. Within this project, by linking the most advanced computational tools to existing observations, we will determine the forces and physical properties associated with plate tectonics. The most important impact will be the training of two Ph.D. students in geophysics and a postdoctoral scholar. They will gain enormous experience with sophisticated numerical methods, supercomputing technologies, and the linkage of data with numerical models. These are essential skills in science and the new knowledge economy. The proposed research will impact several large observational programs by developing hypotheses that could be tested with deep sea drilling under the auspices of IODP and geological sampling and seismic imaging of the Aleutian Island chain under the GeoPRISM project.We propose to test hypotheses for changes in the plate tectonic system with a new generation of geodynamic models and bring new observational constraints to bear on the dynamics of plate motions. We will focus on changes in plate speed & direction and formation of new subduction zones because the observations will allow us to constrain uncertain mantle and lithospheric properties. Specifically, plate motions are likely strongly resisted by bending of the slab in a subduction zone, a force that depends on lithospheric viscosity, but this viscosity remains poorly known and we propose to place tighter bounds on it and other uncertain properties by matching observations in the time domain -- in much the same way that a combination of time-dependent and present day observations of post-glacial rebound are used to constrain the background mantle viscosity. First, we will use generic, fully dynamic 3D models to self-consistently explore the balance between changes in plate motions and changes to subduction and plumes. Second, we will use realistic models to better establish the link between dynamics and detailed geological and geochemical observations of specific examples of subduction initiation. Third, we will build detailed structural models of the mantle and lithosphere in the geological past using an approach that assimilates plate tectonic reconstructions into models of mantle convection along with inverse methods that allow estimation of initial conditions, density anomalies, and viscosity structures. Through these three approaches, we aim to more fully establish the dynamic link between changing plate motions and how they translate into and result from changes in subduction, with specific linkages to geophysical and geological observations. The models will be high resolution (e.g. locally 1 km or less where needed) and fully incorporate the extreme variations in viscosity between the slab and mantle, hinge zone and interface between subducting and over-riding plates.

地球表面通过称为板块构造的过程不断运动。地球表面分为大约十几个构造板块，其中一个板块沿着大断层和断层带相对于其他板块移动（每年几英寸）。尽管这些运动看起来很小，但它们却是地震的原因，包括大地震、造山和沉积盆地的形成。因此，板块构造同时造成了一些最严重的地质灾害以及最大的油气藏的形成。通过这个项目，我们的目标是更好地了解驱动和抵抗板块运动的力量，从而更深入地了解驱动自然灾害和自然资源的力量。在这个项目中，通过将最先进的计算工具与现有的观测结果联系起来，我们将确定与板块构造相关的力和物理特性。最重要的影响将是培养两位博士。地球物理学专业的学生和博士后学者。他们将在复杂的数值方法、超级计算技术以及数据与数值模型的链接方面获得丰富的经验。这些是科学和新知识经济中的基本技能。拟议的研究将通过提出假设来影响几个大型观测计划，这些假设可以在 IODP 的支持下通过深海钻探以及在 GeoPRISM 项目下对阿留申群岛进行地质采样和地震成像进行测试。我们建议测试假设的变化板块构造系统具有新一代地球动力学模型，并为板块运动动力学带来新的观测约束。我们将重点关注板块速度和方向的变化以及新俯冲带的形成，因为这些观测将使我们能够限制不确定的地幔和岩石圈特性。具体来说，板块运动可能会受到俯冲带中板片弯曲的强烈抵抗，这种力取决于岩石圈粘度，但这种粘度仍然知之甚少，我们建议通过匹配时域——与冰期后回弹的时间依赖性和当前观测结果的结合被用来限制背景地幔粘度的方式大致相同。首先，我们将使用通用的、完全动态的 3D 模型来自洽地探索板块运动变化与俯冲和羽流变化之间的平衡。其次，我们将使用现实模型更好地建立俯冲起始具体实例的动力学与详细地质和地球化学观测之间的联系。第三，我们将使用一种将板块构造重建同化到地幔对流模型中的方法以及能够估计初始条件、密度异常和粘度结构的逆方法来建立地质过去的地幔和岩石圈的详细结构模型。通过这三种方法，我们的目标是更全面地建立板块运动变化以及它们如何转化为俯冲变化并导致俯冲变化之间的动态联系，以及与地球物理和地质观测的具体联系。这些模型将具有高分辨率（例如，需要时局部分辨率为 1 公里或更小），并充分考虑板块和地幔之间、铰接带以及俯冲板块和上覆板块之间界面之间粘度的极端变化。