Evaluating the Trench Parallel Flow Hypothesis with Numerical Models of Convection

用对流数值模型评估沟槽平行流假说

• 批准号: 0838026
• 负责人: Scott King
• 金额: $ 25.03万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838026&HistoricalAwards=false
• 关键词: Evaluating; Trench; Parallel; Flow; Hypothesis

EAR-0838026: Evaluating the Trench Parallel Flow Hypothesis with Numerical Models of ConvectionScott D. KingWhen some seismic waves (shear waves) propagate through the upper 200 km of the Earth?s interior, they can be resolved into two orthogonal components that travel at different velocities. This information can be used to predict the pattern of flow in this part of the mantle and, is a key observation behind the hypothesis that mantle material flows parallel to the subducting oceanic plate in the vicinity of subduction zones. Using numerical models we will test recent laboratory fluid tank experiments developed to model this flow and the seismic observations from Earth. Our goal is to identify under what conditions trench parallel flow is observed in the calculations and thus place constraints on the strength and chemistry variations in the subducting slab and mantle. This proposal will test the hypothesis that shear wave splitting observations in subduction zones, both above and below the subducting slab, require that the dominant component of mantle flow that is parallel to the strike of the trench and slab. First we will demonstrate that we can reproduce laboratory tank experiments with a three dimensional numerical model. Next we will test the slab parallel flow hypothesis by addressing the following questions: 1) is slab parallel flow dependent on trench migration rate (i.e., whether or not slabs roll back)?; 2) to what extent does the pattern of mantle flow in the vicinity of a subduction zone depend on slab rheology?; 3) are the olivine to wadsleyite (410 km discontinuity) and the ringwoodite to perovskite plus ferropericlase (660 km discontinuity) phase transformations necessary for slab parallel flow?; and finally 4) is an increase in viscosity in the lower mantle by a factor of 10-30 essential to be able to generate slab parallel flow? We will calculate the finite strain from our numerical results to compare with the seismic observations. We anticipate that strong slabs are more likely to lead to slab parallel flow because strong slabs are more able to resist deforming and hence the mantle will be forced to flow around the slab while weaker slabs are more likely to deform in response to mantle flow and flow around a the slab will not be necessary. We also anticipate that the ringwoodite to perovskite plus ferropericlase phase transformation and an increase in viscosity at the top of the lower mantle will both increase the component of slab parallel flow.

用对流数值模型评估沟槽平行流假设Scott D.当一些地震波（剪切波）传播通过地球上部200公里？在其内部，它们可以分解为两个正交的分量，它们以不同的速度传播。 这一信息可用于预测地幔这一部分的流动模式，是地幔物质在俯冲带附近平行于俯冲洋板块流动这一假设背后的关键观察结果。 使用数值模型，我们将测试最近的实验室流体罐实验开发的模型，这种流动和从地球上的地震观测。 我们的目标是确定在什么条件下，沟槽平行流观察到的计算，从而限制的强度和化学变化的俯冲板和地幔。 这一建议将检验这样一个假设，即在俯冲板块之上和之下的俯冲带中进行剪切波分裂观测，需要地幔流的主要成分平行于海沟和板块的走向。 首先，我们将证明，我们可以重现实验室水槽实验与三维数值模型。 接下来，我们将通过解决以下问题来测试板平行流动假设：1）板平行流动是否取决于沟槽迁移速率（即，板是否回滚）; 2)俯冲带附近的地幔流动模式在多大程度上取决于板块流变学？3)橄榄石到华德士来石（410 km不连续面）和林伍德石到钙钛矿加铁方镁石（660 km不连续面）的相变是否是板片平行流动所必需的？最后4）下地幔中粘度增加10-30倍是能够产生板状平行流的必要条件吗？ 我们将从我们的数值结果计算有限应变，以比较与地震观测。 我们预计，强大的板块更有可能导致板块平行流，因为强大的板块更能够抵抗变形，因此地幔将被迫围绕板块流动，而较弱的板块更有可能变形，以响应地幔流动和围绕板块的流动将是不必要的。 我们还预计，林伍德钙钛矿加铁方镁石相变和下地幔顶部的粘度增加都将增加板片平行流的组成部分。