Mapping variability in the thermo-mechanical structure of the North American Plate and upper mantle

绘制北美板块和上地幔热力结构的变异性

基本信息

批准号：
1736165
负责人：
Benjamin Holtzman
金额：
$ 18.15万
依托单位：
Columbia University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2019-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736165&HistoricalAwards=false
关键词：
Mapping variability thermo mechanical structure

项目摘要

EarthScope provides an unprecedented view into the Earth, enabling the emergence of new interpretations and questions concerning the physics of the Earth's interior. In addition to the purely basic research questions of earth structure, dynamics and evolution, understanding the thermal and mechanical structure is central to understanding societally relevant problems such as the Earth's response to melting ice sheets and rising sea levels, the volcanic potential beneath Yellowstone, and the regional origin of the geothermal gradient for high temperature geothermal energy production. The tectonic plate, or lithosphere, beneath Central and Eastern North America is tectonically stable, but Western North America has a complex recent history (60 million years) of magmatism and deformation, and a correspondingly thin and varied lithosphere structure. The PIs are developing computational methods for interpreting the thermo-mechanical structure (the temperature and the strength) of the upper mantle based on seismic data from the USArray. The core of the method is the systematic calculation of mechanical properties across a vast range of time scale, from seismic wave propagation (seconds) to mantle convection (millions of years) and everything in between. These properties depend on temperature, stress and other thermodynamic "state" variables. When we identify models that are consistent with observations at one time scale, those models constrain physical properties at other time scales. This particular project focuses on how heat from the mantle can corrode the tectonic plates from their underside, influencing where volcanoes and earthquakes occur closer to the surface. The broader impacts of this project fall into three categories: (1) the benefits of development of a unique, very flexible and integrative community code and its uptake by the seismology community; (2) advancement of three early career scientists; and (3) new development of visualization of EarthScope data products for the "SeismoDome" program in the Hayden Planetarium, school curricula and the general public. The aim of this project is to advance the quantitative interpretation of seismic measurements to constrain the thermo-mechanical structure of the shallow upper mantle beneath North America. In particular, the PIs are exploring the possibility that thermal-chemical corrosion occurs by melt infiltration into the plate. Central to this project, the Very Broadband Rheology (VBR) Calculator comprises computational methods intended to form practical and transparent bridges between petrology, seismology, mineral/rock physics and geodynamics. This project expands upon the VBR Calculator for calculation of frequency dependent mechanical properties across the broad range of time scales of geophysical interest, from seismic wave propagation to glacial isostatic adjustment to tectonic plate motions. By using a single approach at multiple locations around the continental US, we enable a direct comparative analysis of 1-D models of regional averages of measurements derived from the seismic wave field, with an emphasis on velocity, attenuation, and receiver functions. Initial results show that there are single forward models that can fit the average Vs "Stable North American" (SNA) lithosphere and asthenosphere. However, the "Tectonic North America" (TNA) velocity profile cannot be fit by a single, simple, steady-state thermal profile, indicating a more complex thermal history that has not reached a steady state. In the proposed research, new 1D open-system two phase flow models with heat advection by melt migration are being developed and added to the VBR library. These models characterize this kind of disequilibrium much further, producing lithospheric corrosion rates with reduced but realistic physics. The open system model results is being used to predict receiver function amplitude and width, enabling the seismic measurements to provide more detailed constraints on the thermal-mechanical structure in each setting.

EarthScope 提供了前所未有的地球视角，使有关地球内部物理学的新解释和问题得以出现。除了地球结构、动力学和演化等纯粹的基础研究问题外，了解热力和机械结构对于理解社会相关问题至关重要，例如地球对冰盖融化和海平面上升的反应、黄石公园下方的火山潜力以及高温地热能生产的地温梯度的区域起源。北美中部和东部下方的构造板块或岩石圈在构造上是稳定的，但北美西部具有复杂的近代岩浆作用和变形历史（6000万年），以及相应薄而多样的岩石圈结构。 PI 正在开发计算方法，用于根据 USArray 的地震数据解释上地幔的热机械结构（温度和强度）。该方法的核心是系统计算大范围时间尺度的力学特性，从地震波传播（秒）到地幔对流（数百万年）以及其间的一切。这些特性取决于温度、应力和其他热力学“状态”变量。当我们确定与某一时间尺度的观测结果一致的模型时，这些模型会限制其他时间尺度的物理特性。这个特殊项目的重点是地幔热量如何从下方腐蚀构造板块，从而影响火山和地震在靠近地表的地方发生。该项目的更广泛影响分为三类：(1) 制定独特、非常灵活和综合的社区规范及其被地震学界采用的好处； (2) 晋升三名早期职业科学家； (3) 为海登天文馆、学校课程和公众的“SeismoDome”计划开发的 EarthScope 数据产品可视化的新开发。该项目的目的是推进地震测量的定量解释，以约束北美下方浅层上地幔的热力结构。特别是，PI 正在探索通过熔体渗透到板材中而发生热化学腐蚀的可能性。该项目的核心是超宽带流变学 (VBR) 计算器，其计算方法旨在在岩石学、地震学、矿物/岩石物理学和地球动力学之间形成实用且透明的桥梁。该项目扩展了 VBR 计算器，用于计算地球物理感兴趣的广泛时间尺度上与频率相关的机械特性，从地震波传播到冰川均衡调整再到构造板块运动。通过在美国大陆各地的多个地点使用单一方法，我们可以对源自地震波场的区域测量平均值的一维模型进行直接比较分析，重点是速度、衰减和接收器函数。初步结果表明，存在可以拟合平均与“稳定北美”(SNA) 岩石圈和软流圈的单一正演模型。然而，“北美构造”（TNA）速度剖面无法用单一的、简单的稳态热剖面拟合，这表明尚未达到稳态的更复杂的热历史。在拟议的研究中，正在开发通过熔体迁移产生热平流的新一维开放系统两相流模型，并将其添加到 VBR 库中。这些模型进一步描述了这种不平衡，产生了岩石圈腐蚀速率，并减少了但真实的物理现象。开放系统模型结果用于预测接收器函数幅度和宽度，使地震测量能够为每种设置中的热机械结构提供更详细的约束。