CSEDI Collaborative Research: Investigating the Nature of the Subcontinental Upper Mantle

CSEDI 合作研究：调查次大陆上地幔的性质

• 批准号: 1361325
• 负责人: Nicholas Schmerr
• 金额: $ 26万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1361325&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Investigating; Nature

Earth's continents have been assembled via amalgamation of land masses over geologic time, eventually forming stable continental interiors, with associated tectonic activity and deformation typically isolated to the periphery of the continent. Over time, successive episodes of deformation in the form of extension, compression, magmatism, accretion, and rifting have left the sub-continental upper mantle with a complex signature of thermal and chemical variability. Many ancient continental areas have been modified by relatively recent dynamic processes, for example active volcanism, rifting, and subduction at continental edges contribute to a complex sub-continental mantle. Of particular interest is the history and influence of melting, melt production, melt migration, and melt storage in sub-continental upper mantle, as it provides a window into past and present dynamical processes, including the formation of continents. This multi-disciplinary project will provide a systematic and geographically-detailed investigation of the dynamical, chemical, and thermal processes at work within the sub-continental upper mantle and their relationships to past and present melting within the Earth. The research team links a primarily undergraduate institution with a research institution and will include training of a postdoctoral researcher, undergraduate researchers through online and face-to-face research collaborations. These connections will be strengthened through long-term cross-institutional research experiences and the inclusion of a pre-service teacher working with the researchers to develop curricular activities describing Earth structure for high school and undergraduate classrooms. This two-year project will develop and apply rock physics models of melt, material mineralogies, and rheologies against observables provided by complementary seismic approaches, providing a comprehensive characterization of the velocity and density structure within the sub-continental upper mantle. The team will investigate the hypothesis that seismic signatures within the sub-continental upper mantle are relatable to past or current episodes of partial melting, and that they bear the fingerprints of thermal, chemical, and dynamical processes brought about by convective motions and mantle flow, both past and present. They will decipher these signals by: 1) using four seismic tools sensitive to absolute shear and compressional wavespeeds, their relative variations, as well as impedance contrasts, discontinuity sharpness, and anisotropic structure, 2) through geodynamic modeling of the seismic observables to quantify whether the presence of melt (or remnant, frozen-in melt) is consistent with the observed seismic structures, and 3) comparison of the inferred models to predictions for mantle rheology, electrical conductivity, temperatures, and composition, and the relationship of variations in these parameters to tectonic evolution and dynamical settings.

地球上的大陆是通过地质时期陆地块的合并而形成的，最终形成稳定的大陆内部，而相关的构造活动和变形通常孤立于大陆的外围。随着时间的推移，以伸展、压缩、岩浆作用、增生和裂谷形式出现的连续变形使次大陆上地幔具有复杂的热和化学变化特征。许多古代大陆地区已经被相对较新的动态过程所改变，例如活跃的火山活动、裂谷和大陆边缘的俯冲作用形成了复杂的次大陆地幔。特别令人感兴趣的是次大陆上地幔的熔融、熔体产生、熔体迁移和熔体储存的历史和影响，因为它为了解过去和现在的动力学过程（包括大陆的形成）提供了一个窗口。这个多学科项目将对次大陆上地幔内的动力学、化学和热过程及其与地球过去和现在融化的关系进行系统和地理上的详细研究。该研究团队将一个主要本科机构与一个研究机构联系起来，并将通过在线和面对面的研究合作培训博士后研究员和本科生研究人员。这些联系将通过长期的跨机构研究经验以及一名职前教师与研究人员合作为高中和本科生课堂开发描述地球结构的课程活动来加强。这个为期两年的项目将开发和应用熔体、材料矿物学和流变学的岩石物理模型，以补充地震方法提供的可观测值，从而提供次大陆上地幔内速度和密度结构的全面表征。该团队将研究以下假设：次大陆上地幔内的地震特征与过去或当前的部分熔融事件有关，并且它们带有对流运动和地幔流带来的热、化学和动力过程的指纹，过去和现在。他们将通过以下方式破译这些信号：1）使用对绝对剪切波速和压缩波速、其相对变化以及阻抗对比、不连续性锐度和各向异性结构敏感的四种地震工具，2）通过地震可观测值的地球动力学建模来量化是否熔体（或残留的、冻结的熔体）的存在与观测到的地震结构一致，3）将推断模型与地幔流变学、电导率、温度、成分，以及这些参数的变化与构造演化和动力学背景的关系。