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

地球上的大陆是通过陆块在地质时期的融合而聚集在一起的，最终形成了稳定的大陆内部，与之相关的构造活动和变形通常孤立在大陆的外围。随着时间的推移，以伸展、挤压、岩浆作用、吸积作用和裂谷作用为形式的连续变形事件使次大陆上地幔具有复杂的热和化学变化特征。许多古老的大陆地区被相对较新的动力学作用所改变，例如活火山作用、裂谷作用和大陆边缘的俯冲作用，形成了复杂的次大陆地幔。尤其令人感兴趣的是次大陆上地幔中熔融、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。这一多学科项目将对次大陆上地幔内的动力、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调查。研究小组将一个主要是本科生的机构与一个研究机构联系起来，并将包括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员。这些联系将通过长期的跨机构研究经验和一名职前教师与研究人员合作，为高中和本科课堂开发描述地球结构的课程活动而得到加强。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，对照补充地震方法提供的可观测数据，提供次大陆上地幔内速度和密度结构的全面表征。该团队将调查一种假设，即次大陆上地幔内的地震特征与过去或现在的部分熔融事件有关，并且它们带有过去和现在对流运动和地幔流动所带来的热、化学和动力学过程的指纹。他们将通过以下方式破译这些信号：1)使用对绝对剪切和压缩波速、它们的相对变化以及阻抗对比、不连续锐度和各向异性结构敏感的四种地震仪器，2)通过对地震观测数据进行地球动力学模拟，以量化熔体(或残余的、冻结在其中的熔体)的存在是否与观测到的地震结构一致，以及3)将推断的模型与地幔流变性、电导率、温度和成分的预测进行比较，以及这些参数的变化与构造演化和动力学环境的关系。

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.