Anisotropy Changes during Deformation and phase Transformations.

地球的大部分地区对地震波的传播是各向异性的。这一点在上地幔中得到了最好的理解，在上地幔中，各向异性归因于橄榄石晶体在对流过程中获得的优先取向。各向异性也存在于地壳中，在地壳中，宏观和微观的裂缝都有显著的影响，在下地幔中(特别是最底部的D？区域)和内核。虽然人们普遍认为各向异性是由变形引起的，但人们对地球深部的详细机制知之甚少。本项目以超高压高温变形实验为重点，探索下地幔主要矿物钙钛矿、后钙钛矿、镁武矿和环木矿的变形机制。金刚石砧胞不仅可以产生压力，还可以产生应力，并且在径向衍射中可以原位观察到首选取向模式的几何变化。最近这些实验可以在压力和温度下进行，我们建议研究取向模式的变化，从而研究变形机制随压力和温度的变化。这样的数据可以用来推断地幔各向异性的发展，并结合地球动力学模型。对塑性模型进行修正，使其考虑到非常大的应变，然后将其应用于地幔条件。虽然重点是下地幔，但我们也计划继续进行最近对石英的研究，其中机械孪生的作用仍然是谜。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再结晶过程中发展得较早，并且只间接受到孪晶的影响。孪生体可以用作古地壳计的一个例子是在陨石撞击或可能的地震破裂的冲击期间。

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.