Elastic anomalies and anelastic dissipation mechanisms associated with phase transitions in minerals.

长期以来，人们一直在研究矿物的弹性性质，因为它们与地球的地震性质有关。人们的兴趣主要集中在与矿物组合变化相关的不连续性上，这导致了我们目前对地幔和地核的分层性质的理解。然而，人们已经认识到，矿物结构的几乎任何变化都会引起弹性常数的变化，对于由原子位移、磁性有序和电子效应驱动的结构转变，弹性常数的变化可能高达数十%。地球物理方法的重大改进也使人们能够更系统地研究衰减效应，最近发表了一些关于衰减随深度变化的模型。本项目将通过提供关于发生衰减的各种机制的基本信息，为这一新方向作出贡献。具体的重点是与矿物及其合成类似物的相变有关的弹性和耗散过程。该项目的目标是(A)使用共振超声光谱仪(RUS)原位测量选定氧化物和硅酸盐在高温和低温下的弹性常数和衰减参数，(B)测试频率和施加的应力对耗散现象的影响，以及(C)进一步发展剑桥的RUS设施，用于测量高温下高耗散样品和含铁矿物。

The elastic properties of minerals have long been investigated for their relevance to the seismic properties of the earth. Interest has largely focussed on discontinuities associated with changes in mineral assemblages and these have led to our present understanding of the layered nature of the mantle and core. It has been recognised, however, that almost any change in the structure of a mineral can give rise to changes in elastic constants and that, for structural transitions driven by displacements of atoms, magnetic ordering and electronic effects, changes in elastic constants can give be as much as tens of percent. Substantial improvements in geophysical methods have also allowed attenuation effects to be investigated more systematically, and a number of models of the variation in attenuation with depth have recently been published. The present project will contribute to this new direction by providing fundamental information on the diversity of mechanisms by which attenuation can occur. The specific focus is on elastic and dissipative processes associated with phase transitions in minerals and their synthetic analogues. The objectives of the project are (a) to measure elastic constants and attenuation parameters for selected oxides and silicates in situ at high and low temperatures using Resonant Ultrasound Spectroscopy (RUS), (b) to test the influence of frequency and applied stress on dissipation phenomena, and (c) to develop further the RUS facility in Cambridge for measurements of highly dissipating samples and for iron bearing minerals at high temperatures.