Collaborative Research: Thermal Structure of Continental Lithosphere Through Time

在地球历史的前20亿年中，地壳形成和生长的过程是什么？太古代-仍然是一个主要的未知数，因为构造和流星轰击删除了大部分岩石记录从那个时候。主要的地壳固结和增长发生在这个时代的结束，但争论仍然继续有关的机制。取得进展的关键是更好地了解此时地壳的热状况，因为许多拟议的模型依赖于热驱动的浮力来解释地壳生长的这一重大事件。为此，这一合作项目将确定岩石在高温下的热特性，以便更好地估计太古代早期地壳的热特性。这些结果将作为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。实验方法是尖端的，将提供有价值的限制，更广泛的社区感兴趣的早期地壳过程建模以及其他领域，如地球物理学，地球动力学和材料科学。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）通过编制K-12教材、教师讲习班和课堂推广，改善STEM教育和教育工作者的发展;（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。该项目得到了构造学计划和美国国家科学基金会国际科学与工程办公室的支持，该项目研究了大陆岩石圈随时间的热结构，特别强调了太古代岩石圈的热特性和流变性。该研究小组将确定下地壳矿物以及Kapuskasing构造带（加拿大安大略）岩石的热扩散率数据，该构造带提供了一个穿过晚太古代绿岩带进入中下地壳的横截面。这些数据将被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传导率的范围，以及它如何随岩石类型和温度而变化。这将涉及：（1）利用激光闪光分析法测量了卡普斯卡辛带及其他地区下地壳矿物和太古代岩石的高温热扩散率，（2）室温光学扫描法与激光闪光分析法的比较，（3）利用差示扫描量热法测量了高温热容，（4）利用差示扫描量热法测量了下地壳矿物和太古代岩石的高温热扩散率，（5）利用差示扫描量热法测量了下地壳矿物和太古代岩石的高温热扩散率。（4）根据岩石的矿物学和孔隙度建立了计算岩石高温导热系数的模型。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。这包括：（1）将热模拟与现有的地表热流数据相结合，以确定基于Kapuskasing剖面的地壳性质;（2）对照岩石记录的压力-温度条件，测试太古代同一剖面的热模型;（3）计算太古代地壳的流变剖面，以确定地壳是软弱的、坚固的还是有变形集中的软弱层。

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.