Collaborative Research: Thermal Structure of Continental Lithosphere Through Time

合作研究：大陆岩石圈随时间变化的热结构

• 批准号: 1524495
• 负责人: Anne Hofmeister
• 金额: $ 6.54万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524495&HistoricalAwards=false
• 关键词: Collaborative; Research; Thermal; Structure; Continental

The processes by which the crust of the Earth formed and grew in the first 2 billion years of earth history ? the Archean eon - remain a major unknown because tectonics and meteor bombardment removed most of the rock record from that time. Major crustal consolidation and growth occurred at the end of this era but debate still continues about the mechanisms. Critical to making progress is a better understanding of the thermal regime of the crust at this time since many proposed models depend on thermal-driven buoyancy to explain this major episode of crustal growth. To that end, this collaborative project would determine the thermal properties of rocks at elevated temperatures in order to better estimate the thermal properties of early Archean crust. The results would be used as the basis for modeling of Archean crust, which would improve our understanding of the strength of the lithosphere in this early phase of crustal growth and evolution. The experimental approach is cutting edge and would provide valuable constraints to the broader community interested in modeling of early crustal processes as well as to other fields such as geophysics, geodynamics, and materials science. The project would advance desired societal outcomes through: (1) full participation of women in STEM; (2) improved STEM education and educator development through development of K-12 teaching materials, teacher workshops, and classroom outreach; (3) development of a globally competitive STEM workforce through graduate and undergraduate student training; and (4) increased partnerships through collaboration with scientists in Australia and Canada. The Tectonics Program and NSF's Office of International Science and Engineering support the project.This project examines the thermal structure of the continental lithosphere over time with particular emphasis on the thermal properties and rheology of Archean lithosphere. The research team will determine thermal diffusivity data for lower crustal minerals as well as for rocks from the Kapuskasing Structural Zone (Ontario, Canada), which provides a cross section through a Late Archean greenstone belt into the mid- to lower-crust. These data will be used as the basis for numerical models of Archean lithosphere rheology. The first objective is to explore the range of thermal diffusivity and conductivity of the continental lower crust, and how it varies with rock type and temperature. This will involve: (1) thermal diffusivity measurement of lower crustal minerals and Archean rocks from the Kapuskasing zone and elsewhere to high temperature by Laser Flash Analysis; (2) comparison of room-temperature optical scanning method and Laser Flash Analysis; (3) heat capacity measurement to high temperature by differential scanning calorimetry; and (4) development of a model for calculating thermal conductivity of rocks to high temperatures from their mineralogy and porosity. The second objective of the project is to estimate the rheology of typical Archean continental crust, its effects on tectonic style, and changes through time. This involves: (1) combining thermal modeling with available surface heat flow data to determine the nature of the crust as based on the Kapuskasing section; (2) test thermal models of this same section in Archean times against pressure-temperature conditions recorded by the rocks; and (3) calculate rheological profiles for Archean crust, to find out if the crust was weak, strong, or had weak layers into which deformation was concentrated.

在地球历史的前 20 亿年里，地壳的形成和生长过程是怎样的？太古宙 - 仍然是一个主要的未知数，因为构造和流星轰击消除了当时的大部分岩石记录。主要的地壳固结和生长发生在这个时代末期，但关于其机制的争论仍在继续。取得进展的关键是更好地了解此时地壳的热状态，因为许多提出的模型依赖于热驱动浮力来解释地壳生长的这一主要事件。为此，该合作项目将确定高温下岩石的热特性，以便更好地估计早期太古代地壳的热特性。研究结果将用作太古代地壳建模的基础，这将提高我们对地壳生长和演化早期阶段岩石圈强度的理解。该实验方法是前沿的，将为对早期地壳过程建模感兴趣的更广泛的社区以及地球物理学、地球动力学和材料科学等其他领域提供有价值的约束。该项目将通过以下方式推进预期的社会成果：(1) 妇女充分参与 STEM； (2) 通过开发 K-12 教材、教师研讨会和课堂推广，改善 STEM 教育和教育工作者发展； (3) 通过研究生和本科生培训，培养具有全球竞争力的 STEM 劳动力； (4) 通过与澳大利亚和加拿大科学家的合作加强伙伴关系。构造计划和美国国家科学基金会国际科学与工程办公室支持该项目。该项目研究大陆岩石圈随时间变化的热结构，特别强调太古代岩石圈的热性质和流变学。研究小组将确定下地壳矿物以及卡普斯卡辛构造带（加拿大安大略省）岩石的热扩散率数据，该构造带提供了穿过晚太古代绿岩带进入中下地壳的横截面。这些数据将用作太古代岩石圈流变学数值模型的基础。第一个目标是探索大陆下地壳的热扩散率和电导率范围，以及它如何随岩石类型和温度变化。这将涉及：（1）通过激光闪光分析测量卡普斯卡辛带和其他地方的下地壳矿物和太古代岩石到高温的热扩散率； (2) 室温光学扫描法与激光闪光分析法的比较； (3)差示扫描量热法测量高温热容； (4) 开发一个模型，用于根据岩石的矿物学和孔隙率计算岩石对高温的热导率。该项目的第二个目标是估计典型太古代大陆地壳的流变性、其对构造样式的影响以及随时间的变化。这涉及：（1）将热模型与可用的地表热流数据相结合，根据卡普斯卡辛剖面确定地壳的性质； (2) 根据岩石记录的压力-温度条件测试太古代同一剖面的热模型； (3)计算太古宙地壳的流变剖面，以确定地壳是软弱的、坚固的还是存在变形集中的软弱层。