Rheology of Lower Mantle Perovskites

下地幔钙钛矿的流变学

• 批准号: 1547556
• 负责人: Donald Weidner
• 金额: $ 48万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547556&HistoricalAwards=false
• 关键词: Rheology; Lower; Mantle; Perovskites

The Earth is a dynamic evolving body, driven by heat sources deep within and enabled by the plastic character of the materials that make up the Earth. As observers on the outer skin of the Earth, even after four and a half billion years, we see constant reminders of this evolution in the form of earthquakes and volcanoes. Even the distinction between ocean and continent owes its origin to this dynamic process. This study is focused on the enabler of this process - the plastic nature of what we consider hard rocks. Over long times at elevated pressure and temperature, rocks behave as liquids. In recent years, tools have evolved that allow us to measure the viscous character of these hard objects at pressures and temperatures that one finds deep in the Earth. These experiments are built around a synchrotron facility that has been built at a national lab. The investigators will use both the National Synchrotron Light Source II at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory. This study will help our understanding of this dynamic evolution of the Earth. A graduate student will be supported and will participate in this research.MgSiO3 in the perovskite crystal structure (bridgmanite) is the most abundant mineral in the Earth and it's calcium counterpart (CaSiO3) is among the five most abundant minerals. The plastic nature of these minerals defines the fluid character of the deep Earth. These properties are both pressure and temperature dependent, and as of yet, unknown. Knowledge of these properties along with proposed temperature models can help constrain dynamics of the Earth evolution and current state. The plastic properties of these minerals is particularly interesting because these minerals are composed of silicon in six coordination with oxygen, while the bulk of materials studied to date have silicon in four coordination with oxygen. The investigating team proposes to study the mechanical properties of these minerals at conditions of pressure and temperature appropriate to the deep Earth. They will focus on defining a quantitative flow law that expresses the plastic properties of these materials. The plasticity of lower mantle minerals at lower mantle conditions of pressure and temperature has been beyond the experimental reach. This has left us with little mineral-based knowledge of the effective viscosity of the lower mantle at the conditions of the anticipated geotherm. Development of new deformation equipment enables a new effort to characterize the quantitative flow law of the high pressure phases at the extremes of pressure and temperature of the top of the lower mantle. This proposal is to study both the Mg and the Ca end-member silicate perovskite at these conditions. This is made possible by a new facility being installed at the new synchrotron, NSLS II, at the Brookhaven National Laboratories. The new facility will provide world class synchrotron X-ray light for these experiments with a new DT25 guideblock in a 1000 ton hydraulic press with deformation capabilities. Using standard X-ray diffraction and imaging tools, the team will be able to define stress and strain rate in the sample at the extreme conditions.

地球是一个动态演化的物体，由地球内部深处的热源驱动，并由构成地球的材料的可塑性特性驱动。作为地球外层的观察者，即使在45亿年后，我们也会看到地震和火山的形式不断提醒我们这种进化。即使海洋和大陆之间的区别也要归功于这一动态过程。这项研究的重点是这一过程的推动者--我们认为坚硬岩石的可塑性。在压力和温度升高的很长一段时间里，岩石表现为液体。近年来，工具的发展使我们能够测量这些坚硬物体在地球深处的压力和温度下的粘性特征。这些实验是围绕国家实验室建造的同步加速器设施进行的。研究人员将同时使用布鲁克海文国家实验室的国家同步辐射光源II和阿贡国家实验室的高级光子光源。这项研究将有助于我们理解地球的这种动态演化。一名研究生将得到支持并参与这项研究。钙钛矿晶体结构中的镁SiO_3是地球上最丰富的矿物，它的钙对应物(CaSiO_3)是五种最丰富的矿物之一。这些矿物的可塑性决定了地球深处的流体性质。这些性质都与压力和温度有关，到目前为止还是未知的。对这些特性的了解以及提出的温度模型可以帮助约束地球演化和当前状态的动态。这些矿物的可塑性特别有趣，因为这些矿物是由硅与氧六配位组成的，而到目前为止研究的大部分材料都有硅与氧四配位。调查小组建议在适合地球深处的压力和温度条件下研究这些矿物的机械性能。他们将专注于定义一种表达这些材料的塑性属性的定量流动定律。在下地幔压力和温度条件下，下地幔矿物的塑性已超出实验范围。这使得我们对预期地温条件下下地幔的有效粘度几乎没有基于矿物的知识。新的变形设备的发展使得能够对下地幔顶部在压力和温度极端情况下的高压相的定量流动规律进行新的努力。本方案是在这些条件下同时研究镁和钙端元硅酸盐钙钛矿。这是由布鲁克海文国家实验室新的同步加速器NSLS II安装的新设施实现的。新设施将为这些实验提供世界级的同步辐射X射线光，并在具有变形能力的1000吨水压机上安装新的DT25导块。使用标准的X射线衍射和成像工具，研究小组将能够确定极端条件下样品中的应力和应变率。