Collaborative Research: Rheology of the Earth's Transition Zone - An Integrated Approach

合作研究：地球过渡带的流变学 - 综合方法

• 批准号: 1606528
• 负责人: James Hirth
• 金额: $ 18万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1606528&HistoricalAwards=false
• 关键词: Collaborative; Research; Rheology; Earth; Transition

Heat convection in the Earth is controlled by flow of the hot, but solid mantle. This convection drives plate tectonics, generating major societal hazards (e.g., earthquakes, volcanic eruptions, tsunamis, etc.) and controls the compositional and thermal evolution of the planet. Since the early 1960s, quantifying the deformation properties of mantle rocks has been a major goal in experimental Earth Sciences. Advancement has been limited by technology, owing to serious difficulties in conducting experiments involving deformation of minerals at the extreme pressures and temperatures prevailing in Earth's deep interior. The upper-mantle (top 410 km) consists of peridotites, rocks comprised dominantly of olivine, i.e., the semi-precious gem known as peridot. In the transition zone (410-670 km depth) at pressure in excess of 140,000 atm, olivine is no longer stable and transforms into high-pressure minerals, wadsleyite and ringwoodite, which have comparable compositions but denser structures. Decades of experimental work have provided strong constraints on olivine plasticity, yet little is known about the viscosity of minerals in the transition-zone. The aim of the present project is to provide accurate computational models for the viscosity of Earth's transition zone, which will integrate new experimental data on wadsleyite and ringwoodite obtained in state-of-the art high-pressure deformation devices set at synchrotron facilities. These experiments, involving newly developed devices and analytical techniques, are at the forefront of research on the mechanical behavior of materials at high pressure. Besides advancing our understanding of mantle convection, this program will provide support and training in modern experimental science to one graduate student as well as undergraduate students. All the new experimental and analytical tools will become available to other scientists, advancing our general knowledge in high-pressure research. The team's results will find direct applications in Geophysics and Seismology, and broader applications in Materials Science. Flow laws for Earth materials provide vital constraints on mantle dynamics, while knowledge of deformation mechanisms at the atomic scale provides insights into crucial observables such as seismic anisotropy. The complexity of the stress field within deforming rocks, which varies from grain to grain as plastic properties are anisotropic, can now be observed in situ using new high-pressure devices coupled with X-ray synchrotron radiation, and addressed by self-consistent mean-field modeling. In this project, the investigators will take advantage of these recent developments to address the plasticity of the transition zone. Specifically, they will study the flow properties of wadsleyite and ringwoodite as a function of iron and water contents, and constrain strength contrasts with olivine, using the Deformation-DIA apparatus and the newly developed D-TCup and DT-25. In situ X-ray radiography and diffraction will be used to measure strain, stress and texture (i.e., lattice preferred orientation). The new flow laws will be integrated into models for the effective viscosity and seismic anisotropy of the transition-zone. Modeling efforts will benefit from the second-order (SO) method, a recent improvement in mean-field schemes which describes accurately highly non-Newtonian materials, such as silicates. The models will account for stress-field heterogeneities due to crystal orientations, complex deformations mechanisms (dislocation glide and diffusion), incorporate several minerals, and improve confidence for extrapolation of results to geologic strain rates. The model construction will be flexible, allowing integration of additional phases and flow law parameters as they become available in the future. The outcome will give crucial insights on transition-zone viscosity, and the crystal preferred orientations that produce seismic anisotropy.

地球中的热对流由热但坚实的地幔的流动控制。这种对流驱动板块构造，产生重大的社会危害（例如，地震，火山喷发，海啸等），并控制了行星的组成和热演化。自1960年代初以来，量化地幔岩石的变形特性一直是实验地球科学的主要目标。由于在地球深层内部盛行的极端压力和温度下，涉及涉及矿物质变形的实验的严重困难，进步受到技术的限制。 上层（前410公里）由橄榄岩组成，岩石主要由橄榄石组成，即被称为橄榄石的半宝石。在超过140,000 atm的压力下的过渡区（410-670 km深度）中，橄榄石不再稳定，并且转化为高压矿物质，wadsleyite和ringwoodite，它们具有可比的成分，但结构较密集。 数十年的实验性工作为橄榄石可塑性提供了强烈的限制，但是对于过渡区中矿物质的粘度知之甚少。本项目的目的是为地球过渡区的粘度提供准确的计算模型，该模型将整合在Synchrotron设施上设置的最先进的高压变形设备中获得的Wadsleyite和Ringwoodite的新实验数据。这些涉及新开发的设备和分析技术的实验位于高压下材料机械行为的研究的最前沿。除了促进我们对地幔对流的理解外，该计划还将为一名研究生以及本科生提供现代实验科学的支持和培训。所有新的实验和分析工具都将用于其他科学家，从而促进我们在高压研究方面的一般知识。该团队的结果将在地球物理学和地震学上找到直接应用，并在材料科学中更广泛的应用。地球材料的流量定律对地幔动力学有至关重要的限制，而原子尺度上的变形机制的知识则提供了对关键可观察物（例如地震各向异性）的见解。现在，可以使用新的高压设备以及X射线同步辐射来解决变形岩石内应力场的复杂性，随着塑料特性是各向异性的，随着塑料特性为各向异性，其变形岩石的复杂性，随着颗粒的变化，随着颗粒的变化而变化，并且可以在原位观察到。现场建模。在这个项目中，研究人员将利用这些最近的发展来解决过渡区的可塑性。具体而言，他们将使用变形 - dia设备以及新开发的D-TCUP和DT-25研究Wadsleyite和Ringwoodite与铁和水含量的函数的流动特性，并约束与橄榄石的强度对比。 原位X射线射线照相和衍射将用于测量应变，应力和质地（即晶格优选方向）。 新的流量定律将集成到过渡区有效粘度和地震各向异性的模型中。建模工作将受益于二阶（SO）方法，这是近期平均场方案的改进，该方案准确地描述了高度非牛顿材料，例如硅酸盐。由于晶体取向，复杂的变形机制（位错滑动和扩散），融合了几种矿物质，并提高了将结果推断到地质应变速率，因此该模型将考虑应力场异质性。模型的构建将是灵活的，可以在将来可用时集成其他阶段和流量法参数。该结果将对过渡区粘度和产生地震各向异性的晶体优选方向产生至关重要的见解。