"COLLABORATIVE RESEARCH: Compositional and thermal variations in the mantle transition zone from integrated seismological and petrological investigations"

“合作研究：地震学和岩石学综合研究中地幔过渡带的成分和热变化”

• 批准号: 0551384
• 负责人: Yingwei Fei
• 金额: $ 17.24万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0551384&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Compositional; thermal; variations

It has long been recognized that the mantle transition zone plays an important role in mantle dynamics. The seismic discontinuities near 410 and 660 km depth, which mark the top and bottom of the transition zone, are commonly associated with the mineralogical phase transformations from olivine to wadsleyite and from ringwoodite to perovskite plus magnesiowustite, respectively. Because of the negative Clapeyron slope of the phase transformation near 660 km depth, the density change associated with the phase transformation has a strong influence on convection in the mantle, by resisting mantle upwelling and downwelling through the transition zone. Knowledge of the transition zone comes primarily from two sources: High-pressure experiments that constrain the phase relations and elastic coefficients of likely mantle minerals as a function of pressure, temperature, and composition; and seismic observations of the depth and sharpness of the seismic discontinuities and the velocity structure of the transition zone. The combination of these two approaches has yielded the basic structure and composition of the mantle. In this collaborative project, scientists from University of Rhode Island, Carnegie Institution of Washington, National Taiwan University and Ehime University (Japan) integrate seismological and petrological approaches to study the mantle transition zone in three distinctly different tectonic settings (continental keel, hotspot, and subduction zone) beneath southern Africa and central South America. The project aims to address several important questions in earth sciences: What is the thickness of the southern African continental roots? Are there excess volatiles (water) in the transition zone beneath these continental roots? What is the depth of origin of the Tanzania hotspot? Is the transition zone a water filter? How does a depleted and cold subducting slab affect the transition zone structure?Researchers in this project use a recently developed finite-frequency seismic tomography method to sharpen the images of the velocity structure in the transition zone. The new method yields a more robust velocity structure than conventional methods based on ray theory. The improved tomographic images are important for obtaining more coherent seismic phases from mantle discontinuities and better estimates of the transition zone thickness and depth to the discontinuities. The seismic observations and their initial interpretations provide the basis for high-pressure experiments optimally designed to understand the mantle conditions of the different tectonic features. The study focuses on measurements of the thickness of the transition zone, which is one of the parameters that can be measured most precisely by seismic data analyses and by high-pressure experiments through the measurements of the differential pressure of the olivine-wadsleyite and the postspinel transition boundaries. Together with thermodynamic modeling, results from high-pressure experiments on both simplified and real mantle compositions provide constraints on small-scale lateral variations in mantle temperature and composition. Through graduate student training in seismic data analyses and high-pressure experiments, the seismologists and experimentalists in this project gain deep understanding of the problems and strengths in each other's field. Such understanding is essential to the Collaborative Study of Earth's Deep Interior (CSEDI).

长期以来，人们已经认识到地幔过渡区在地幔动力学中起着重要作用。 在410和660 km深度附近的地震不连续性标记了过渡区的顶部和底部，通常与从橄榄石到Wadsleyite的矿物学相变相关，分别从Ringwoodite以及从Ringwoodite到Perovskite Plus Perovskite Plus Magnesiowustite。 由于相变的阴性斜率接近660 km，因此与相变相关的密度变化通过抵抗过渡区的地幔上升和向下流，对地幔中对流的密度变化对对流有很大影响。 过渡区的知识主要来自两个来源：高压实验，这些实验限制了可能地幔矿物的相位关系和弹性系数，这是压力，温度和成分的函数；对地震不连续性的深度和清晰度的地震观察以及过渡区的速度结构。 这两种方法的组合产生了地幔的基本结构和组成。在这个合作项目中，罗德岛大学的科学家，华盛顿州卡内基研究所，国家台湾大学和埃希姆大学（日本）整合了地震学和质学方法，以研究三种鲜明不同的构造环境中的地幔过渡区（大陆龙骨，热点和热点，和热点，和热点，以及俯冲区）南部非洲和中美洲中部。 该项目旨在解决地球科学中的几个重要问题：南部非洲大陆根源的厚度是多少？ 在这些大陆根部下方的过渡区中是否有多余的挥发物（水）？ 坦桑尼亚热点的起源深度是什么？过渡区是滤水器吗？ 耗尽和冷的俯冲平板如何影响过渡区的结构？该项目的研究人员使用最近开发的有限频率地震层析成像方法来锐化过渡区中速度结构的图像。 与基于射线理论的常规方法相比，新方法产生的速度结构更强。 改进的层析成像图像对于从地幔不连续性中获得更连贯的地震阶段以及对过渡区厚度和深度到不连续性的更好估计很重要。 地震观测及其初始解释为最佳设计的高压实验提供了基础，以了解不同的构造特征的地幔条件。 该研究的重点是测量过渡区的厚度，这是可以通过地震数据分析和通过测量橄榄石 - 沃德斯利岩的差异和后跨度后的差异测量来确切测量的参数之一。过渡边界。 与热力学建模一起，对简化和真实地幔组成的高压实验产生的结果为地幔温度和成分的小规模横向变化提供了约束。 通过在地震数据分析和高压实验中的研究生培训，该项目中的地震学家和实验者对彼此领域的问题和优势深入了解。 这种理解对于对地球深处（CSEDI）的协作研究至关重要。