Effects of temperature-dependent thermal diffusivity on shear instability in a viscoelastic zone: implications for faster ductile faulting and earthquakes in the spinel stability field
Effects of temperature-dependent thermal diffusivity on shear instability in a viscoelastic zone: implications for faster ductile faulting and earthquakes in the spinel stability field
复制标题
温度相关的热扩散率对粘弹性区剪切不稳定性的影响：对尖晶石稳定性场中更快的延性断层和地震的影响
DOI：
10.1016/s0012-821x(00)00239-9
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Y. Kaneda
中科院分区：
文献类型：
--
作者：
J. Branlund;M. Kameyama;D. Yuen;Y. Kaneda
新的热扩散系数模型的引入促使我们重新研究具有真实流变、温度相关热扩散系数（κ(T)）和粘性耗散的一维粘弹性剪切区模型。尽管剪切区的热扩散系数在空间上随κ(T)和粘性加热呈非均匀分布，但对于模型中使用的网格分辨率而言，κ(T)的空间分布并不影响剪切区的演化。当温度高于室温时，热扩散率降低。相对于使用室温热扩散系数的情况，较低的热扩散系数导致剪切区在空间上略有变薄，并且加速了不稳定的发生。增大κ(T)的非线性会增强剪切区变薄和失稳加速；增强的量取决于温度、矿物学和剪切加热的速率。尖晶石的流变性使剪切带比橄榄石更不稳定，但不稳定与稳定的边界对材料性质的变化很敏感。晶粒尺寸的减小不会影响失稳的时间尺度，除非晶粒尺寸的减小导致扩散蠕变成为主要的变形机制。粘弹性热机械不稳定性发生在几百年到几千年的时间尺度上。在大多数板坯中，在1200 K以上的温度下，尖晶石区域没有发现不稳定性。同样，上地幔深处橄榄石的剪切不稳定性在高于1100k的温度下不会发生。
The introduction of a new model of thermal diffusivity has motivated us to reinvestigate a one-dimensional viscoelastic shear zone model with realistic rheology, temperature-dependent thermal diffusivity (κ(T)) and viscous dissipation. Although thermal diffusivity in the shear zone is spatially heterogeneous with κ(T) and viscous heating, the spatial distribution of κ(T) does not affect shear zone evolution for the mesh resolution used in the model. As temperatures increase above room temperature, thermal diffusivity decreases. The lower thermal diffusivity causes a slight spatial thinning of the shear zone and an acceleration of the onset of instability relative to cases using a room temperature value of thermal diffusivity. Increasing the nonlinearity of κ(T) enhances shear zone thinning and speed-up of instability; the amount of enhancement depends on temperature, mineralogy and the rate of shear heating. The rheology of spinel creates a more unstable situation for the shear zone than that of olivine, but the boundary separating instability and stability is sensitive to changes in material properties. A decrease in the grain size does not influence the timescale of instability, unless grain size reduction causes diffusion creep to be the dominant deformation mechanism. Viscoelastic thermal–mechanical instabilities occur on timescales ranging from a few hundred to several thousand years. In most slabs, no instability is found to occur in spinel regions at temperatures above 1200 K. Likewise, shear instability in olivine at upper mantle depths will not occur at temperatures greater than 1100 K.