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

地球上的大陆是在地质时期通过陆地块的合并而形成的，最终形成了稳定的大陆内部，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、吸积和裂谷等形式出现的连续变形，给次大陆上地幔留下了复杂的热化学变化特征。许多古老的大陆地区已经被相对较新的动态过程所改变，例如活跃的火山作用、裂谷作用和大陆边缘的俯冲作用形成了一个复杂的次大陆地幔。特别令人感兴趣的是熔融、熔体产生、熔体迁移和熔体储存在次大陆上地幔中的历史和影响，因为它为过去和现在的动力过程提供了一个窗口，包括大陆的形成。这个多学科的项目将提供一个系统的和地理上详细的调查动力学，化学和热过程的工作在次大陆上地幔和它们的关系，过去和现在在地球内部融化。该研究团队将一个主要的本科院校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，培训一名博士后研究员、本科生研究人员。这些联系将通过长期的跨机构研究经验得到加强，并包括一名职前教师与研究人员一起开发描述高中和本科教室地球结构的课程活动。这个为期两年的项目将根据互补地震方法提供的观测数据，开发和应用熔融、物质矿物学和流变学的岩石物理模型，提供次大陆上地幔内速度和密度结构的全面表征。该小组将调查以下假设：次大陆上地幔的地震特征与过去或现在的部分融化事件有关，并且它们具有过去和现在对流运动和地幔流动带来的热、化学和动力过程的指纹。它们将通过以下方式解读这些信号：1)利用四种对绝对切变和纵波速度及其相对变化、阻抗对比、不连续清晰度和各向异性结构敏感的地震工具；2)通过地震观测资料的地球动力学建模，量化熔体（或残余、冻结熔体）的存在是否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、这些参数的组成及其变化与构造演化和动力环境的关系。

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.