Anisotropy Changes during Deformation and phase Transformations.

地球上的大片区域对于地震波的传播是各向异性的。这对于上地幔来说是最好的理解，在那里各向异性是由于在对流过程中获得的橄榄石晶体的优先取向所致。各向异性也存在于地壳中，宏观和微观断裂对地壳和下地幔(尤其是最下部的D？区域)，以及内核。虽然人们普遍认为各向异性是由变形引起的，但对地球深处的详细机制却知之甚少。超高压高温变形实验是探索下地幔主要矿物钙钛矿、后钙钛矿、镁辉石和环形辉石变形机制的重点。金刚石砧座单元不仅可以产生压力，还可以产生应力，在径向衍射中，可以原位观察到择优取向图案的几何变化。最近，这些实验既可以在压力下进行，也可以在温度下进行，我们建议研究取向图案的变化，从而研究变形机制随压力和温度的变化。然后，这些数据可以结合地球动力学模型，用来推断地幔各向异性的发展。塑性模型将进行修改，以考虑非常大的应变，然后将其应用于地幔条件。虽然重点是在下地幔，我们也计划继续最近关于石英的工作，在那里机械孪生的作用仍然是个谜。从我们最新的相变实验中可以看出，石英织构的三角性在变形和重结晶过程中发展较早，仅间接受孪生的影响。双胞胎可以用作古表层岩石计的一个例子是在陨石撞击或可能的地震破裂造成的冲击期间。

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.