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

我们计划研究超糜棱岩，这是非常细粒度的断层岩在韧性剪切带，同时使用EDS和EBSD，以确定相分布和主导的变形机制。该样品之前已经使用EBSD和光学显微镜进行了分析，但分辨率限制阻止了对更细粒度区域的详细分析。有人怀疑，扩散蠕变（原子迁移沿着晶界）是在这些区域的主要机制，使用FEG-SEM的分析可以验证这一假设。在这次科学研究中，我们在静冈大学建立了SEM-EBSD系统。虽然我们对超糜棱岩的研究仍在进行中，但在橄榄岩的研究方面，我们可以得到一些重要的结果。日本东北弧弧后地区上地幔的地震各向异性：Ichinomegata橄榄岩捕虏体的岩石物理分析日本东北弧已部署了一个密集的地震台站网络，以调查地幔楔结构。为了获得独立的岩石物理约束，我们确定了地震性质的Ichinomegata地幔捕虏体从弧后地区，从地幔岩石圈火山喷发的表面。我们计算了橄榄石和辉石捕虏体的晶体择优取向和单晶弹性常数。实测横波分裂的小幅度（在包体夹带区延迟时间为0.22 s）可以用地幔包体在约20 km厚的水平各向异性层中的平均地震属性来解释，表明地幔岩石圈可能是地震各向异性的主要来源之一;这一层可能与最上层地幔岩石圈的变形有关，这是由于沿日本弧东北部沿着的弧后扩张。

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.