CAREER: When Subduction Fails - Dynamical Models of Oceanic Plateau Collision and Crustal-Fragment Accretion

职业：当俯冲失败时——海洋高原碰撞和地壳碎片吸积的动力学模型

• 批准号: 0748818
• 负责人: Magali Billen
• 金额: $ 48.83万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0748818&HistoricalAwards=false
• 关键词: CAREER; When; Subduction; Fails; Dynamical

Most studies of subduction dynamics attempt to determine the processes responsible for sustaining long-term subduction of typical oceanic lithosphere. While active subducting slabs have seismicity evident of intense internal deformation to various depths, the slab continues to directly transmit stresses to the surface plate. Only under special conditions does the slab become sufficiently weak or the positive buoyancy of the surface plate sufficiently large to cause subduction to fail. By looking at cases when subduction fails we can learn about the processes required to sustain longterm subduction. Three-dimensional thermo-mechanical models are being used to address two processes of subduction failure: 1) How does attempted oceanic plateau subduction cause subduction to fail? 2) How does crustal-fragment loss occur during normal subduction? These studies focus on the first-order, essential processes, such as the basic rheologic layering of the oceanic plate and localization processes, phase transformations that change rheology and/or density, the size and geometry of structures, and obliquity of convergence. The educational components of this project build directly on the research objectives, by using the dynamical model results as synthetic data sets to help students master 3D spatial thinking skills. Laboratory and homework exercises are being developed from the numerical model results that ask students to create a cross section of the subsurface structure from mapped data of structure orientations (strike, dip) taken from the synthetic 3D models. This part of the exercise simulates the interpretive exercise students normally carry out with actual mapped data taken in the field. However, unlike the field experience, the students are then given the opportunity to correct their initial cross section after exploring the actual 3D structure using visualization software, which allows them to create cross sections of any orientation and view the 3D structures as isosurfaces. In addition, a new feature is being added to the visualization software that allows the surface of the 3D numerical data to be sliced with any pre-defined 2D topographic surface (instead of a simple plane). This tool allows students to explore directly how topography influences the surface outcrop of 3D subsurface structures (e.g., intersection of a dipping fault with a valley versus a ridge).

大多数俯冲动力学研究都试图确定维持典型海洋岩石圈长期俯冲的过程。虽然活跃的俯冲板片具有明显的地震活动性，表明不同深度的强烈内部变形，但板片继续直接将应力传递到表面板块。只有在特殊条件下，板块才会变得足够脆弱，或者表面板块的正浮力足够大，从而导致俯冲失败。通过观察俯冲失败的案例，我们可以了解维持长期俯冲所需的过程。三维热机械模型被用来解决俯冲失败的两个过程：1）尝试的海洋高原俯冲如何导致俯冲失败？ 2）正常俯冲过程中地壳碎片损失是如何发生的？这些研究重点关注一阶基本过程，例如海洋板块的基本流变分层和定位过程、改变流变和/或密度的相变、结构的尺寸和几何形状以及会聚倾斜度。该项目的教育部分直接建立在研究目标之上，通过使用动态模型结果作为合成数据集来帮助学生掌握 3D 空间思维技能。实验室和家庭作业练习是根据数值模型结果进行的，要求学生根据从合成 3D 模型获取的结构方向（走向、倾角）的映射数据创建地下结构的横截面。这部分练习模拟了学生通常使用现场获取的实际映射数据进行的解释练习。然而，与现场体验不同的是，学生在使用可视化软件探索实际 3D 结构后，有机会纠正其初始横截面，这使他们能够创建任何方向的横截面并将 3D 结构视为等值面。此外，可视化软件中还添加了一项新功能，允许使用任何预定义的 2D 地形表面（而不是简单的平面）对 3D 数值数据的表面进行切片。该工具允许学生直接探索地形如何影响 3D 地下结构的地表露头（例如，倾斜断层与山谷与山脊的交叉点）。