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A new method for mapping stresses in mantle rocks: Dislocation density from electron-backscatter diffraction

绘制地幔岩石应力的新方法：电子背散射衍射的位错密度

基本信息

批准号：
NE/M000966/1
负责人：
Lars Norman Hansen
金额：
$ 49.27万
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FM000966%2F1
关键词：
new method mapping stresses mantle

项目摘要

The viscous flow of solid rock in Earth's deep interior fundamentally controls a variety of large-scale processes ranging from the formation of tectonic plate boundaries to the timescale of sea-level rise associated with receding ice sheets to the dynamics of the deepest portions of earthquake-generating faults. The most common approach to learning about the flow of rocks at extreme conditions is to conduct experiments in a laboratory on small samples at relatively short timescales. The relevant processes in the Earth, however, occur over many kilometers and millions of years, scales much larger than those accessible in the laboratory. For scientists to know how best to extrapolate from small scales to large scales when predicting the behavior of real Earth processes, they need a robust understanding of the microscopic physical mechanisms controlling the flow of rocks at extreme conditions.Several sophisticated models exist describing the viscous behavior of rocks. However, considerable uncertainty persists regarding their details, and there is a corresponding lack of suitable analytical techniques to test those details. Therefore, we propose to adapt a new technique for quantifying the intricacies of the viscous flow of rocks. This technique, recently developed for analyzing small-scale structures in metals, allows defects in the constituent crystals-known as dislocations-to be mapped quickly and precisely at high resolution in an electron microscope. We will conduct laboratory deformation experiments on single crystals of olivine, the dominant mineral in the upper mantle, to establish a relationship between the density of dislocations and the deformation conditions. Determining this relationship will enable us to map deformation conditions at very fine scales in synthetic and natural olivine-rich rocks deformed in variety of settings. We will then compare the results of this mapping to predictions from current models for olivine deformation, using the results to rule out models that do not capture the essential physical processes and to refine and update the ones that do. The project will thus yield a new method in the Earth sciences applicable to a wide range of minerals, and it will address several outstanding problems in the deformation of upper-mantle rocks.

地球内部深处固体岩石的粘性流动从根本上控制着各种大规模的过程，从构造板块边界的形成到与冰盖消退相关的海平面上升的时间尺度，再到地震发生断层最深处的动力学。了解极端条件下岩石流动的最常见方法是在实验室中以相对较短的时间尺度对小样本进行实验。然而，地球上的相关过程发生在许多公里和数百万年的时间里，规模比实验室中可获得的要大得多。为了让科学家们知道如何在预测真实的地球过程的行为时最好地从小尺度外推到大尺度，他们需要对极端条件下控制岩石流动的微观物理机制有一个坚实的理解。然而，其细节仍然存在相当大的不确定性，相应地也缺乏适当的分析技术来测试这些细节。因此，我们建议采用一种新的技术来量化岩石的粘性流动的复杂性。这项技术是最近发展起来的，用于分析金属中的小尺度结构，它允许在电子显微镜中以高分辨率快速精确地绘制组成晶体中的缺陷（称为位错）。我们将对上地幔中的主要矿物橄榄石单晶进行实验室变形实验，以建立位错密度与变形条件之间的关系。确定这种关系将使我们能够映射变形条件在非常精细的尺度在合成和天然富含橄榄石的岩石变形在各种设置。然后，我们将比较这一映射的结果与当前橄榄石变形模型的预测，使用结果来排除那些没有捕捉到基本物理过程的模型，并改进和更新那些能够捕捉到的模型。因此，该项目将在地球科学中产生一种适用于各种矿物的新方法，并将解决上地幔岩石变形方面的几个突出问题。