Collaborative Research: Evaluating the Roles of Melt Migration and Mantle Flow in Lithospheric Evolution: The Colorado Plateau as a Geodynamic Laboratory for EarthScope

合作研究：评估熔体迁移和地幔流在岩石圈演化中的作用：科罗拉多高原作为 EarthScope 的地球动力学实验室

• 批准号: 0952202
• 负责人: Benjamin Holtzman
• 金额: $ 12.14万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952202&HistoricalAwards=false
• 关键词: Collaborative; Research; Evaluating; Roles; Melt

1. Technical descriptionThis project focuses on the generation and segregation of melt at the lithosphere-asthenosphere boundary (LAB), with the aims of (1) characterizing the physical nature of the boundary and (2) constraining the processes that determine its form and evolution. Specifically, the LAB may be substantially modified by processes that are dominantly thermomechanical (e.g., physical delamination of dense parts by drips or shear), or dominantly thermochemical (e.g. rejuvenation by melt impregnation and conversion of depleted material into enriched, partially molten material). This work builds on recent observations suggesting that melt segregation at and migration along the LAB can substantially modify the thermal, chemical, and mechanical properties of the boundary in a "deformation-enhanced thermo-chemical rejuvenation" process. This project explores the geodynamic implications of these ideas by developing a phenomenological description of stress-driven melt segregation based closely on experimental observations, that will be incorporated into fluid-dynamical models of mantle deformation beneath the Colorado Plateau (CP) in the western US. The research builds upon geologic and seismic observations that constrain the distribution and geometry of melt in the CP region, specifically comparing the plateau-margins to the interior. The PIs are interpreting these observations using numerical models of a suite of processes: 1) spatial variations in plate thinning of the CP and surrounding regions, 2) possible convective instability of dense regions of the plate, and 3) motion of the CP lithospheric "keel" through the underlying asthenosphere. These investigations are being coupled with seismic anisotropy observations from surface waves across the USArray to infer mantle deformation scenarios beneath the CP.2. Non-technical description of broader impact and significance.One of the fundamental discoveries that the scientific community hopes EarthScope will help achieve is a clearer picture of the "shape" of the North American plate; that is, a measurement of lithosphere thickness and an understanding of the spatial variability in both the thermal and chemical properties of the plate. The base of the lithosphere is an elusive boundary that does not coincide with an easily imaged seismic discontinuity. As data from the USArray component of EarthScope are analyzed to construct seismic models of the upper mantle beneath the tectonically active western US, an important goal for the scientific community is to interpret seismic observations in terms of the structure and dynamics of the plate-mantle interface. A fundamental ambiguity that plagues seismic interpretations is the relative importance of temperature, composition, and fluids (e.g., melt) in controlling the isotropic and anisotropic seismic structure of the upper mantle. This project is developing physics-based models of deformation at the base of the North American plate that can be used to help interpret seismic observations. The project is providing important training for a graduate student in building quantitative models of the Earth and is broadening participation of underrepresented groups in the earth sciences. The combination of fluid dynamics and the experimentally based phenomenology developed here is an innovation that can be generalized to other geodynamic settings. Because the structure and evolution of North America and the CP in particular is of broad public interest, the PIs will produce compelling images from seismic observations, models and interpretive illustrations with pedagogical intent. These images will be utilized in public education and outreach (as well as scientific publications) at museums and national parks in the Southwest, New York and elsewhere.

1. 技术描述该项目重点研究岩石圈-软流圈边界（LAB）熔体的产生和分离，目的是（1）表征边界的物理性质，（2）限制决定其形式和演化的过程。 具体来说，LAB可以通过主要是热机械的工艺（例如，通过滴落或剪切对致密部件进行物理分层）或主要的热化学工艺（例如，通过熔体浸渍和将耗尽的材料转化为富集的部分熔融材料进行再生）进行实质性修改。 这项工作建立在最近的观察基础上，表明在“变形增强热化学再生”过程中，熔体偏析和沿 LAB 的迁移可以显着改变边界的热、化学和机械性能。 该项目通过密切基于实验观察的应力驱动熔体偏析的现象学描述来探索这些想法的地球动力学含义，该描述将被纳入美国西部科罗拉多高原（CP）下方地幔变形的流体动力学模型中。该研究建立在地质和地震观测的基础上，这些观测限制了中部地区熔体的分布和几何形状，特别是对高原边缘与内部进行了比较。 PI 正在使用一系列过程的数值模型来解释这些观测结果：1) 中部地区及其周围区域板块减薄的空间变化，2) 板块密集区域可能存在的对流不稳定性，以及 3) 中部地区岩石圈的运动“龙骨”穿过下面的软流圈。这些研究与 USArray 表面波的地震各向异性观测相结合，以推断 CP.2 下方的地幔变形情景。更广泛影响和意义的非技术性描述。科学界希望 EarthScope 能够帮助实现的基本发现之一是更清晰地了解北美板块的“形状”；也就是说，测量岩石圈厚度并了解板块热特性和化学特性的空间变化。 岩石圈的底部是一个难以捉摸的边界，与容易成像的地震不连续性不重合。 随着对 EarthScope USArray 组件的数据进行分析，以构建构造活动活跃的美国西部下方上地幔的地震模型，科学界的一个重要目标是根据板块-地幔界面的结构和动力学来解释地震观测结果。困扰地震解释的一个基本模糊之处是温度、成分和流体（例如熔体）在控制上地幔各向同性和各向异性地震结构中的相对重要性。 该项目正在开发北美板块底部基于物理的变形模型，可用于帮助解释地震观测结果。该项目为研究生提供建立地球定量模型的重要培训，并扩大地球科学领域代表性不足群体的参与。 这里开发的流体动力学和基于实验的现象学的结合是一项创新，可以推广到其他地球动力学设置。由于北美尤其是中部地区的结构和演变具有广泛的公众利益，PI 将从地震观测、模型和具有教学目的的解释性插图中生成引人注目的图像。这些图像将用于西南部、纽约和其他地方的博物馆和国家公园的公共教育和宣传（以及科学出版物）。