Ultrasonic Velocity and Density Measurements on Silicate Melts at Upper Mantle Pressures

上地幔压力下硅酸盐熔体的超声波速度和密度测量

• 批准号: 1045630
• 负责人: Baosheng Li
• 金额: $ 27.65万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-02-01 至 2016-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1045630&HistoricalAwards=false
• 关键词: Ultrasonic; Velocity; Density; Measurements; Silicate

Melts exist in the Earth's interior and play important roles in various geological processes, such as volcanic eruption and lava flow, the formation and migration of magmas in the mantle, and the convection of liquid outer core. For instance, precise knowledge of sound speed of melts helps us diagnose the presence of melts in the Earth's deeper depths, and the information about the density contrasts between melts and crystals determines the sink/float of crystals in magmas in the evolution of the Earth. Characterization of the behavior and properties of melts at the Earth's upper mantle depths, however, remains a challenging task. The proposed project will (i)develop new techniques for precise sound speed measurements using ultrasonic interferometric method on liquids/melts at pressures of the Earth's upper mantle, and (ii)conduct measurements on melts of olivine, the most abundant mineral of the Earth's upper mantle. Currently, density measurements using static sink-float and shock wave methods have been the major tools in constraining melt densities at mantle pressures to test the density crossovers, such as between the basic silicate liquids and the co-existing olivine. To date, sound velocity measurements on melts have only been conducted at ambient pressure using varying-sample-depth technique; measurements at high pressures, however, have been hindered by the lack of means of precisely measuring melt thickness or varying the sample depths. The PIs have developed the techniques to overcome these difficulties by using an X-radiographic imaging technique. They propose to conduct measurements on the iron end-members as well as intermediate compositions of Mg2SiO4-Fe2SiO4. These measurements and the derived thermal equation of states will complement and provide benchmarking data for static (sink-float, X-ray absorption), shock wave, and computer simulations, allowing for a refined characterization of the locations of crystal/liquid density crossovers in the upper mantle, transition zone, and lower mantle.

熔体存在于地球内部，并在各种地质过程中起重要作用，例如火山喷发和熔岩流，地幔中岩浆的形成和迁移以及液体外核的对流。例如，精确的熔体声速知识有助于我们诊断地球深度深处的熔体存在，并且有关熔体和晶体之间密度对比的信息决定了地球进化中岩浆中晶体的水槽/浮标。然而，熔体在地球上地幔深度上的行为和特性的表征仍然是一项艰巨的任务。拟议的项目将（i）开发新技术，以在地球上地幔压力下使用超声干涉方法在液体/熔体上进行精确的音速测量，以及（ii）对橄榄石熔体的熔体，地球上层最丰富的矿物的熔体进行测量。当前，使用静态水槽循环和冲击波方法的密度测量是限制地幔压力下熔体密度以测试密度交叉的主要工具，例如基本的硅酸盐液体和共存的橄榄石之间的密度。迄今为止，仅使用不同样本深度技术在环境压力下进行了熔体的声速测量。然而，由于缺乏精确测量熔体厚度或改变样品深度的方法，高压下的测量受到了阻碍。 PI通过使用X射线照相成像技术开发了克服这些困难的技术。他们建议对铁端成员进行测量以及MG2SIO4-FE2SIO4的中间组合物。这些测量值和态的态热方程将补充并提供基准测量数据（水槽循环，X射线吸收），冲击波和计算机模拟，从而可以对上层，过渡区和下层的晶体/液体密度交叉的位置进行精致表征。