Collaborative Research: Thermal Structure of Continental Lithosphere Through Time

在地球历史的前20亿年里，地壳形成和增长的过程是什么？太古宙——仍然是一个主要的未知数，因为构造和流星轰击移除了那个时期的大部分岩石记录。主要的地壳巩固和增长发生在这个时代的末期，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的浮力来解释地壳生长的这一主要时期。为此，这个合作项目将确定高温下岩石的热性质，以便更好地估计早期太古宙地壳的热性质。这些结果将作为太古宙地壳模型的基础，有助于我们对这一早期地壳生长和演化阶段岩石圈强度的认识。实验方法是最前沿的，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促进预期的社会成果：(1)女性充分参与STEM；(2)通过开发K-12教材、教师研讨会和课堂外展，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。构造学计划和NSF的国际科学与工程办公室支持这个项目。该项目考察了大陆岩石圈随时间的热结构，特别强调了太古宙岩石圈的热性质和流变学。研究小组将确定下地壳矿物的热扩散率数据，以及来自Kapuskasing构造带（加拿大安大略省）的岩石的热扩散率数据，该构造带提供了贯穿晚太古宙绿岩带进入中至下地壳的截面。这些数据将作为太古宙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系数和导热系数的范围，以及它如何随岩石类型和温度而变化。这将涉及：(1)通过激光闪光分析测量来自Kapuskasing带和其他地方的下地壳矿物和太古宙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)差示扫描量热法测高温热容；(4)根据岩石的矿物学和孔隙度，建立了计算岩石高温热导率的模型。该项目的第二个目标是估计典型太古宙大陆地壳的流变学，其对构造样式的影响及其随时间的变化。这包括：(1)结合热模拟和可用的表面热流数据，以Kapuskasing剖面为基础确定地壳的性质；(2)对照岩石记录的压力-温度条件，对同一剖面太古宙时期的热模型进行测试；(3)计算太古宙地壳流变剖面，判断地壳是弱、强、还是有集中变形的弱层。

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.