In-situ Acoustic Velocity Measurement on Mantle Phase Transitions

地幔相变的原位声速测量

• 批准号: 0635860
• 负责人: Baosheng Li
• 金额: $ 24.02万
• 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: 2007
• 资助国家: 美国
• 起止时间: 2007-02-01 至 2011-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635860&HistoricalAwards=false
• 关键词: situ; Acoustic; Velocity; Measurement; Mantle

Phase transitions in the mantle resulting from pressure and temperature changes with increasing depth are believed to be responsible for the velocity discontinuities observed in seismic studies. In this project, elasticity of candidate mantle phases undergoing phase transitions at P-T conditions relevant to the Earth's mantle are studied using an integrated ultrasonic interferometry and synchrotron X-radiation technique in the multi-anvil apparatus. These experiments allow for simultaneous measurements of lattice parameter (hence specific volume and density) and P and S wave velocities across the phase transitions of mantle phases up to 26 GPa and 1800K. The phase transitions to be investigated include olivine to wadsleyite, wadsleyite to ringwoodite, and the dissociation of ringwoodite perovskite plus magnesiowustite which are believed to be predominantly responsible for the seismic discontinuities at 410-, 520-, and 660-km depths. Of great significance is that, by directly measuring the velocities of multi-phase aggregates with pyrolitic compositions, robust velocity contrasts across these phase transitions can be derived at the physical and chemical conditions relevant to these discontinuities in the mantle. The uncertainties originating from the complexities in the calculation of physical properties for a hypothetically mixed aggregate, such as extrapolations using equation of state for individual phases, iron partitioning change and their effect on elasticity and phase equilibrium, can be eliminated. As a result, the comparison of the current results with seismic data will place a tight constraint on the candidate mantle compositions responsible for the observed magnitude and lateral variations at these discontinuities.

地幔中的相变是由压力和温度随深度增加而引起的，这被认为是地震研究中观察到的速度不连续的原因。在这个项目中，我们在多砧座装置上利用集成的超声干涉和同步辐射技术研究了在与地幔相关的P-T条件下发生相变的候选地幔相的弹性。这些实验允许同时测量晶格参数(因此比体积和密度)以及P波和S波在26 Gpa和1800K的地幔相变中的速度。要研究的相变包括橄榄石到瓦兹利石，瓦兹利石到林木，以及环木钙钛矿和镁闪石的解离，它们被认为是410公里、520公里和660公里深度地震不连续的主要原因。具有重要意义的是，通过直接测量具有热解成分的多相集合体的速度，可以在与地幔中的这些不连续有关的物理和化学条件下得出跨越这些相变的强劲的速度对比。由于混合骨料物理性质计算的复杂性，如使用状态方程对单个相进行外推、铁的分配变化及其对弹性和相平衡的影响，这些不确定因素可以消除。因此，目前的结果与地震数据的比较将对造成这些不连续面上观测到的震级和横向变化的候选地幔成分施加严格的约束。