CSEDI Collaborative Research: Understanding the origins of MORB geochemical heterogeneity using constraints from seismic tomography and geodynamic modeling

CSEDI 合作研究：利用地震层析成像和地球动力学建模的约束了解 MORB 地球化学非均质性的起源

• 批准号: 1800324
• 负责人: Barbara Romanowicz
• 金额: $ 9.88万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-05-01 至 2023-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1800324&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Understanding; origins

The chemical composition of lavas erupted under the water at mid ocean ridges, where new seafloor is created as tectonic plates spread apart, is influenced by the temperature and composition of the underlying mantle from which these melts are generated. The proposed work examines correlations between mid ocean ridge basalt (MORB) chemistry and images of Earth's interior produced using seismic tomography. It uses large-scale numerical models of mantle flow to connect surface observations with past and present mantle structure. The proposed work has three components. First, it examines the distributions of helium isotopes and other geochemical indicators of mantle temperature at spreading centers and how these are related to temperature and compositional variations in the sub-oceanic mantle. Second, it explores the flow history of mantle material that is sampled at spreading centers. Third, it addresses how the mid ocean ridges in different ocean basins have sampled the mantle since the breakup of the supercontinent Pangea. The project will provide new information about how variations in seismic velocity beneath the ocean basins are related to the variations in chemical composition of MORB, and how upper mantle variations in composition and temperature are related to deeper mantle structure.Different disciplines make distinct contributions to our understanding of the dynamics of Earth's mantle. In particular, relating the distribution of geochemical and seismological heterogeneity at the global scale has been a challenge because of the different wavelengths sampled in these two types of approaches: local, for geochemistry, long wavelength, for seismology. Recently, progress has been made in both fields, with resolution reaching sub-1000 km scale in global seismic tomography, and a more complete geochemical sampling along mid-ocean ridges, allowing the investigation of patterns at wavelengths commensurate with the seismic imaging. Concurrently, progress has been made in developing methodologies for realistic geodynamic modeling of mantle circulation in 3D, incorporating constraints from seismology and surface observables (e.g. plate motions, topography, and the geoid). Tying these elements together to better constrain the flow history of material sampled at ridges is becoming feasible at the present time. The proposed work will produce new geochemical datasets, tomographic models, and results from geodynamic models that will be distributed to the broader geoscience community for further analysis and in a format that permits immersive 3D visualization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在大洋中脊的水下喷发出的熔岩的化学成分受到产生这些熔体的底层地幔的温度和成分的影响。由于构造板块的分离，新的海底在那里形成。提出的工作研究了海中脊玄武岩（MORB）化学成分与地震层析成像产生的地球内部图像之间的相关性。它使用大尺度的地幔流动数值模型将地表观测与过去和现在的地幔结构联系起来。拟议的工作有三个组成部分。首先，研究了扩张中心地幔温度的氦同位素和其他地球化学指标的分布，以及它们与海底地幔温度和成分变化的关系。其次，探索扩展中心取样的地幔物质的流动历史。第三，研究了自泛大陆分裂以来，不同洋盆的洋中脊是如何对地幔进行采样的。该项目将提供有关海洋盆地下地震速度变化如何与MORB化学成分变化相关的新信息，以及上地幔成分和温度变化如何与更深的地幔结构相关的新信息。不同的学科对我们理解地幔动力学有不同的贡献。特别是，在全球尺度上联系地球化学和地震学非均质性的分布一直是一项挑战，因为在这两种方法中采样的波长不同：局部，用于地球化学，长波长，用于地震学。最近，这两个领域都取得了进展，全球地震层析成像的分辨率达到了1000公里以下的尺度，并且沿着大洋中脊进行了更完整的地球化学采样，从而可以在与地震成像相对应的波长上进行模式研究。同时，结合地震学和地面观测（如板块运动、地形和大地水准面）的约束，在开发三维地幔环流的真实地球动力学建模方法方面取得了进展。将这些元素结合在一起，以更好地约束在脊上取样的物质的流动历史，目前已变得可行。拟议的工作将产生新的地球化学数据集、层析模型和地球动力学模型的结果，这些数据将分发给更广泛的地球科学社区进行进一步分析，并以一种允许沉浸式3D可视化的格式。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Primitive Helium Is Sourced From Seismically Slow Regions in the Lowermost Mantle

原始氦源自最下地幔的地震缓慢区域

• DOI: 10.1029/2019gc008437
• 发表时间: 2019
• 期刊: Geosystems
• 作者: Williams, C. D.;Mukhopadhyay, S.;Rudolph, M. L.;Romanowicz, B.
• 通讯作者: Romanowicz, B.