4D physical models of migrating mid-ocean ridges: Implications for shallow mantle flow, melt distribution and seafloor topography

洋中脊扩张、板块俯冲和地幔柱等形式的板块构造和行星对流驱动了固体地球-水圈-大气系统在地质时间尺度上的自然质量/能量循环，为当今全球气候变化提供了重要背景。据估计，由这些地质驱动力产生的岩浆过程提供给水圈/大气的碳中，大约有一半是由世界上8万公里长的洋中脊系统的板块扩张造成的。本项目将利用物理实验室设备，通过刻画海洋中脊板块运动和岩浆生成的基本过程，不仅在三维空间上，而且在时间上进行演化，开发改进的对流地幔流驱动模型。以前试图将地幔流动、岩浆产生和质量/能量流动与地球海洋/大气联系起来的模型通常只是在二维上进行的。最近的地质和地球物理数据以及模型升级的结合清楚地表明，二维模型的表示是不够的。该项目包括为研究生提供支持，并通过罗德岛大学本科生研究经验项目为来自代表性不足群体的本科生提供研究机会，包括当地美国原住民学生。物理模型还将为大学、学校和公众提供直观的地球深部过程体验。该项目将设计和构建地球动力学模型，并在已建立和测试的实验室设备上进行扩展，以探索与海洋中部扩张脊有关的基本四维过程。虽然数值模型存在分辨率问题，并且是一组误差通常完全未知的控制方程的近似值，但物理模型特别有用，因为它们允许在感兴趣的区域（例如在山脊下的熔体生成区域）具有自然时间依赖性的高分辨率3D物理，并允许模型边界伪影最小化。该项目将研究基本的海脊几何形状和具有更复杂属性的模型，如洋中脊迁移及其在上地幔动力学、海底地形和洋中脊岩浆过程中的作用。这台新的实验室设备将研究几个先前提出但未经验证的模型：(1)主要构造板块下方上地幔的不对称上升流，(2)跨迁移的洋中脊系统的海山的不对称分布，(3)偏置洋中脊的岩浆分割和熔体清除，以及(4)洋中脊转换交叉点的增强上升流。迁移脊装置的设计将允许转换偏移量、扩展速率和迁移矢量，这些可以缩放到已知中洋脊系统的全频谱。实验室模型和模拟结果套件将提供对海洋中脊的4D特征的独特测试，并提供对海洋中扩张中心的地球动力学和融化过程的见解。这些结果预计将对理解基本的地幔过程以及这些过程如何在地质时间尺度上影响水圈/大气系统的质量/能量通量具有重要意义。这些模型还将为相关领域提供重要的基准，如地幔性质、地震层析成像和绝对板块运动估计。

Plate tectonics and planetary convection in the form of mid-ocean ridge spreading, plate subduction and mantle plumes drive the natural mass/energy cycling of the solid earth-hydrosphere-atmosphere system over geological time scales and provides important context for present day global climate change. It is estimated that roughly half of the carbon provided to the hydrosphere/ atmosphere from magmatic processes generated by these geological drivers is attributed to plate spreading of the world's 80,000 km long mid-ocean ridge system. This project will use a physical laboratory apparatus to develop improved models of convective mantle flow driving plate motion and magmatic production beneath mid-ocean ridges by characterizing the essential processes not only in 3-dimensions but also their time evolution. Previous models that attempt to connect mantle flow, magma production and mass/energy flux to Earth's oceans/atmosphere have typically only been conducted in two-dimensions. The combination of recent geological and geophysical data and model upgrades clearly show that 2D model representations are insufficient. The project includes support for a graduate student and research opportunities for undergraduates from under-represented groups including local native american students through the Research Experience for Undergraduates program at the University of Rhode Island. Physical models will also provide a visually accessible experience of deep earth processes for university, school and public outreach audiences.This project will design and construct geodynamic models that build and expand on established and tested laboratory apparatus for exploring the essential four-dimensional processes related to mid-ocean spreading ridges. While numerical models suffer from resolution issues and are approximations to a set of governing equations with errors that are usually entirely unknown, physical models are particularly useful as they permit high resolution 3D physics with a natural time dependency in regions of interest (e.g. in the melt generation regions beneath ridges) and allow model boundary artifacts to be minimized. The project will investigate both basic ridge geometries and models with more complex attributes such as mid-ocean ridge migration and its role on upper mantle dynamics, seafloor topography, and mid-ocean ridge magmatic processes. This new lab apparatus will investigate several previously proposed but untested models: (1) asymmetric upwelling of the upper mantle below the leading tectonic plate, (2) asymmetric distribution of seamounts across migrating mid-ocean ridge systems, (3) magmatic segmentation and melt scavenging of offset mid-ocean ridges, and (4) enhanced upwelling at ridge-transform intersections. The design of the migrating ridge apparatus will allow transform offsets, spreading rates, and migration vectors that can scale to the full spectrum of known mid-ocean ridge systems. The laboratory model and suite of modeling results will provide a unique test of the 4D character of mid-ocean ridges and provide insight into geodynamic and melting processes at mid-ocean spreading centers. Results are expected to have important implications for understanding fundamental mantle processes and how these influence mass/energy fluxes to the hydrosphere/atmosphere systems on geologic time scales. These models will also provide important benchmarks for related fields, such as mantle properties, seismic tomography and estimates of absolute plate motions.