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，在各种地质过程中发挥着重要作用，如火山爆发和熔岩流，地幔岩浆的形成和迁移，以及液态外核的对流。例如，对熔体声速的精确了解有助于我们诊断地球深处是否存在熔体，而熔体和晶体之间的密度对比信息决定了地球演化过程中岩浆中晶体的下沉/漂浮。然而，表征地球上地幔深处熔体的行为和性质仍然是一项具有挑战性的任务。拟议项目将（一）开发新技术，利用超声波干涉测量法对地球上地幔压力下的液体/熔体进行精确的声速测量，（二）对地球上地幔最丰富的矿物橄榄石熔体进行测量。目前，密度测量使用静态沉-浮和冲击波的方法已经成为主要的工具，在地幔压力下的约束熔体密度测试的密度交叉，如基本硅酸盐液体和共存的橄榄石之间。迄今为止，熔体声速测量仅在环境压力下使用变样品深度技术进行;然而，由于缺乏精确测量熔体厚度或改变样品深度的手段，在高压下的测量受到阻碍。PI已经开发了通过使用X射线成像技术来克服这些困难的技术。他们建议对铁端元以及Mg 2SiO 4-Fe 2SiO 4的中间成分进行测量。这些测量和推导出的热状态方程将补充和提供静态基准数据（浮沉，X射线吸收），冲击波和计算机模拟，允许在上地幔，过渡区和下地幔的晶体/液体密度交叉的位置的精细表征。