An experimental study on grain-size evolution during phase transformations in the mantle transition zone and its influence on rheological properties

地幔过渡带相变过程中晶粒尺寸演化及其对流变特性影响的实验研究

• 批准号: 1445356
• 负责人: Shun-ichiro Karato
• 金额: $ 29.99万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-01 至 2017-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1445356&HistoricalAwards=false
• 关键词: experimental; study; grain; size; evolution

It is now well appreciated that Earth's interior are vigorously convecting at the geological time scale. This "mantle convection" is the most important process that controls the way in which Earth evolves and continents move. As materials move in the deep interior of Earth, crystal structure of minerals changes to new ones caused by a large pressure inside of the deep Earth. These phase transitions likely change the deformability (viscosity) of materials and the main goal of this project is to evaluate the degree to which these phase transitions might change the deformability. Our focus is the changes in the size of minerals caused by phase transitions, that could modify the viscosity of materials by several orders of magnitude. The results of this study will provide a new insight into the role of phase transitions in the deep interior of Earth in modifying the nature of mantle convection.Phase transitions that occur in Earth's transition zone likely have a large influence on mantle convection. A phase transition could affect convection through its effect on density and viscosity. Among the various mechanisms by which viscosity of materials change, we focus on the change in grain-size that could change the viscosity up to ~10 orders of magnitude. We will conduct systematic experiments on the olivine to wadsleyite transitions following various P-T-t paths (P: pressure, T: temperature, t: time) and determine the size and spatial distribution of new grains. We will interpret these results in terms of a model of microstructural evolution during a phase transition, and apply these results to evaluate the change in viscosity of a subducting slab in the transition zone.

现在，人们非常感谢地球内部在地质时间尺度上有力地对流。这种“地幔对流”是控制地球进化和大洲移动方式的最重要过程。随着材料在地球深内部移动，矿物质的晶体结构会变成由深地球内部巨大压力引起的新晶体。这些相变可能会改变材料的可变形性（粘度），该项目的主要目标是评估这些相变可以改变可变形性的程度。我们的重点是相变引起的矿物质大小的变化，可以通过几个数量级来改变材料的粘度。这项研究的结果将为地球对流的性质在地球深层内部的深层内部中的作用提供新的见解。地球过渡区域中发生的相转变可能对地幔对流有很大影响。相变可以通过对对流对密度和粘度的影响影响对流。在材料粘度发生变化的各种机制中，我们集中在晶粒大小的变化上，这些变化可能会将粘度更改为约10个数量级。我们将在橄榄石上进行系统实验，以遵循各种P-T-T路径（P：压力，T：温度，T：时间），并确定新晶粒的大小和空间分布。我们将根据相变过程中的微结构演化模型来解释这些结果，并应用这些结果来评估过渡区俯冲平板的粘度变化。