Anisotropy Changes during Deformation and phase Transformations.

对于地震波的传播，地球的大部分区域是各向异性的。这是最好的理解为上地幔，各向异性归因于在对流过程中获得的橄榄石晶体的优选取向。各向异性也存在于地壳中，宏观和微观断裂有显着的影响，并在下地幔（特别是最低的D？区）和内核。虽然人们普遍认为各向异性是由变形引起的，但对地球深部的详细机制却知之甚少。本项目的重点是在常压和高温下进行变形实验，以探索下地幔主要矿物钙钛矿、后钙钛矿、镁铁矿和林伍德铁矿的变形机制。金刚石压砧单元不仅可以用来产生压力，而且还可以产生应力，并且在径向衍射中可以原位观察到优选取向图案的几何形状变化。最近，这些实验可以在压力和温度下进行，我们建议研究取向图案的变化，从而与压力和温度的变形机制。这些数据可以用来推断地幔各向异性的发展，结合地球动力学模型。塑性模型将被修改，以考虑到非常大的应变，然后将其应用到地幔条件。虽然重点是在下地幔，我们也计划追求最近的工作对石英的作用，机械孪生仍然是谜。从我们最新的相变实验看来，石英织构的三角形在变形和再结晶过程中发展得较早，并且只受到孪晶的间接影响。一个例子，双胞胎可以被用来作为古压力计是在冲击陨石的影响或可以想象的地震破裂。

Large regions of the earth are anisotropic for propagation of seismic waves. This is best understood for the upper mantle where anisotropy is attributed to preferred orientation of olivine crystals, attained during convection. Anisotropy is also present in the crust, where macroscopic and microscopic fractures have a significant influence, and in the lower mantle (particularly the lowermost D? zone), and the inner core. While there is general agreement that anisotropy is caused by deformation, the detailed mechanisms in the deep earth are poorly understood. Deformation experiments at ultrahigh pressure and temperature are the focus of this project to explore deformation mechanisms in the principal lower mantle minerals perovskite, postperovskite, magnesiowuestite and ringwoodite. Diamond anvil cells can be used not only to produce pressure but also stress, and in radial diffraction geometry changes in the preferred orientation pattern can be observed in situ. Most recently these experiments can be performed both at pressure and temperature and we propose to study variations of orientation patterns and thus deformation mechanisms with pressure and temperature. Such data can then be used to infer the development of anisotropy in the mantle, combined with geodynamic models. Plasticity models will be modified to take very large strain into account and then applied it to mantle conditions. While emphasis is on the lower mantle, we also plan to pursue recent work on quartz where the role of mechanical twinning remains enigmatic. From our latest phase transformation experiments it appears that the trigonality of quartz textures develops early during deformation and recrystallization and is only indirectly affected by twinning. One example where twins can be used as a paleopiezometer is during shock by meteorite impact or conceivably seismic rupture.