Deformation mechanism of rocks due to intense strain rate in shear zone

为了确定其物相分布和主要变形机制，我们计划利用EDS和EBSD同时对韧性剪切带中的超细粒断层岩进行研究。之前已经使用EBSD和光学显微镜对样品进行了分析，但分辨率的限制阻碍了对更细粒度区域的详细分析。人们怀疑扩散蠕变（沿晶界的原子迁移）是这些区域的主要机制-使用FEG-SEM的分析可以验证这一假设。在本次科研中，我们在静冈大学建立了SEM-EBSD系统。虽然我们对超长岩的分析还在进行中，但我们可以在橄榄岩研究方面得到一些重要的结果。日本东北部弧后地区最上层地幔地震各向异性：一野橄榄岩包体岩石物理分析在日本东北部弧上部署了密集的地震台站网络，以研究地幔楔状结构。为了获得独立的岩石物理约束条件，我们确定了弧后地区的Ichinomegata地幔包体的地震性质，这些包体是火山喷发从地幔岩石圈带到地表的。从橄榄石和辉石晶体优选取向和单晶弹性常数计算了捕虏体的地震性质。在约20 km厚的水平各向异性层中，地幔捕虏体的平均地震性质可以解释s波分裂的小震级（夹带捕虏体区域的延迟时间为0.22 s），表明地幔岩石圈可能是地震各向异性的主要来源之一；该层可能与日本东北弧后扩张引起的上地幔岩石圈变形有关。

We planned to investigate ultramylonite, which is very-fine grained fault rocks in ductile shear zones, using simultaneous EDS and EBSD in order to determine the phase distribution and the dominant deformation mechanisms. The sample had been analysed previously using both EBSD and light microscopy, but resolution limitations prevented a detailed analysis of the finer grained zones. It was suspected that diffusion creep (atomic migration along grain boundaries) was the dominant mechanism in these zones-this analysis using a FEG-SEM could verify this hypothesis. During this Scientific Research, we established a SEM-EBSD system in Shizuoka University. Although our analyses on ultramylonites are still in progress, we could get some important results on peridotite study.Seismic anisotropy in the uppermost mantle, back-arc region of the northeast Japan arc : Petrophysical analyses of Ichinomegata peridotite xenolithsA dense network of seismic stations has been deployed across the northeast Japan arc to investigate mantle wedge structures. To attain independent petrophysical constraints, we determined the seismic properties of Ichinomegata mantle xenoliths from the back-arc region that were brought to the surface from the mantle lithosphere by volcanic eruptions. We calculated the seismic properties of the xenoliths from olivine and pyroxene crystal-preferred orientations and single crystal elastic constants. The small magnitude of measured S-wave splitting (delay time of 0.22 s in the area where the xenoliths were entrained) can be explained by the average seismic properties of mantle xenoliths for an approximately 20-km thick horizontal anisotropic layer, indicating that the mantle lithosphere could be one of the dominant sources of seismic anisotropy; this layer is possibly related to deformation in the uppermost mantle lithosphere due to back-arc spreading along the northeast Japan arc.