Collaborative Research: Variations in Upper-Mantle Temperature, Deformation, and Melting Inferred from the Seismic Structure of the Atlantic Basin

该项目将研究大西洋盆地下上地幔的热状态和成分状态、熔融过程和变形。这些属性将推断从新的，高分辨率，三维层析模型的地震速度，衰减和各向异性的大西洋上地幔。目前对海洋上地幔的了解大部分来自太平洋盆地的区域地震模型。然而，大西洋和太平洋的扩张速率和板块速度的差异表明，两个盆地下的地幔中发生了不同的动力学过程。新模型将受到大西洋海盆内或边缘的事件和台站的基波和高阶表面波相位延迟和振幅的大型数据集的限制。 这项研究试图解决三个关键问题：（1）是什么控制了地震结构作为深度和海底年龄的函数？这些特性是否仅归因于温度，还是必须考虑成分和熔体？(2)是什么控制了沿轴和离轴地震异常？它们是否反映了一个可变的地幔源，温度和成分起着什么作用？(3)与较慢的板块速度有关的地幔组构是否比较快的扩张速度所产生的地幔组构更弱、更易变？这些问题中的每一个都需要与快速扩张的太平洋上地幔进行比较，它们共同提供了一个机会，可以研究地震结构的可能扩展速率依赖性以及可能产生它的机制。最终的地震模型最终将用于推断温度，成分，部分熔融含量和变形状态，在矿物物理实验和其他数据集（例如玄武岩化学、测深和大地水准面高度）的约束的帮助下。 研究的非技术性描述根据板块构造理论，地球？地球坚硬的外壳被划分为相对缓慢移动的构造板块，这些板块由板块下方地幔中炽热、脆弱的岩石（软流圈）内的对流驱动。 我们对控制这种从板块内坚硬岩石到板块下弱变形岩石的突然转变的过程知之甚少。 仅仅是因为软流层的岩石更热吗？它们是部分熔化的，还是含有使它们变弱的成分（水或其他挥发物）？ 由于地震产生的地震波对温度和其他弱化过程敏感，我们可以使用地幔结构的地震成像来解决这些问题。 区分这些过程将使我们能够更好地了解地球如何？的构造体系的发展和演变，并阐明了削弱和熔融过程中产生的地质灾害，如断裂带和火山系统。

This project will investigate the thermal and compositional state, melting processes, and deformation of the upper mantle beneath the Atlantic basin. These properties will be inferred from new, high-resolution, three-dimensional tomographic models of seismic velocity, attenuation, and anisotropy of the Atlantic upper mantle. Much of what is currently known about the oceanic upper mantle comes from regional seismic models of the Pacific basin. However, differences in the spreading rates and plate velocities of the Atlantic and Pacific oceans suggest that different dynamical processes are occurring in the mantle beneath the two basins. The new models will be constrained by large data sets of fundamental and higher-mode surface-wave phase delay and amplitude from events and stations located within or on the margins of the Atlantic basin. This research seeks to address three key issues: (1) What controls the seismic structure as a function of depth and seafloor age? Can these properties be attributed solely to temperature, or must composition and melt also be considered? (2) What controls along-axis and off-axis seismic anomalies? Do they reflect a variable mantle source, and what roles do temperature and composition play? (3) Is the mantle fabric associated with slower plate velocities weaker and more variable than that produced by faster spreading rates? Each of these questions invites a comparison with the faster-spreading Pacific upper mantle, and together they present an opportunity to investigate possible spreading-rate dependence of seismic structure as well as the mechanisms that might produce it. The final seismic models will ultimately be used to infer temperature, composition, partial melt content, and deformation state, aided by constraints from mineral-physics experiments and other data sets such as basalt chemistry, bathymetry, and geoid height. Non-Technical Description of ResearchAccording to the theory of plate tectonics, the Earth?s rigid outer shell is divided into tectonic plates that slowly move relative to one another, driven by convection currents within hot, weak rocks in the mantle beneath the plates (the asthenosphere). We have a poor understanding of the processes that control this abrupt transition from rigid rocks within the plate to weak deforming rocks beneath the plate. Is it simply that the asthenospheric rocks are hotter? Are they partially molten, or do they contain compositional components (water or other volatiles) that weaken them? Because seismic waves generated by earthquakes are sensitive to temperature and other weakening processes, we can use seismic imaging of mantle structure to address these questions. Distinguishing between these processes will allow us to better understand how the Earth?s tectonic system developed and evolved over time, and also illuminates the weakening and melting processes that produce geologic hazards such as fault zones and volcanic systems.