Plastic Deformation and Lattice-Preferred Orientation in Wadsleyite: Experimental Constraints on the Rheology and Dynamics of Mantle Transition Zone

地幔过渡带在地幔动力学中起着关键作用。最近的高分辨率地震层析成像显示了对流与地幔过渡带之间丰富多样的相互作用。了解这种相互作用的本质所需要的关键数据之一是该层中材料的流变性能。然而，塑性变形的实验研究是困难的，并且在该地区还没有材料的定量流变数据。在这个项目中，研究人员将对wadsleyite进行第一次控制良好的定量流变测量，wadsleyite是浅层过渡带中最丰富的矿物。本研究将使用一种新开发的RDA（旋转Drickamer装置）。对大应变进行变形实验，不仅可以获得流变学数据，还可以获得变形几何与地震各向异性的关系。研究结果将有助于理解上地幔与过渡带的力学耦合（影响与地幔对流相关的大地面异常）、过渡带板块的可变形性以及深震的分布和机制。关于wadsleite的格优选取向与流动几何形状之间关系的结果将是根据流动几何形状解释该地区地震各向异性的第一个数据集。

The transition zone of the Earth's mantle plays a key role in mantle dynamics. Recent high-resolution seismic tomography shows rich variety of interaction of convection current with the mantle transition zone. One of the key data that are needed to understand the nature of this interaction is the rheological properties of materials in this layer. However, experimental studies of plastic deformation are difficult and there has been no quantitative rheological data on materials in this region. In this project, the investigators will conduct the first well-controlled quantitative rheological measurements on wadsleyite, the most abundant mineral in the shallow transition zone. A newly developed apparatus, RDA (rotational Drickamer apparatus), will be used in this study. Deformation experiments will be conducted to large strains to obtain not only the rheological data but also the relationship between deformation geometry and seismic anisotropy. The results from this research will help understand the mechanical coupling between the upper mantle and the transition zone (that affects the geoid anomalies associated with mantle convection) as well as the deformability of slabs in the transition zone and the distribution and the mechanisms of deep earthquakes. The results on the relation between the lattice-preferred orientation of wadsleyite and flow geometry will be the first data set to interpret seismic anisotropy in terms of flow geometry in this region.