Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water fugacity corrections
Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water fugacity corrections
复制标题
石英位错蠕变流动定律的理论推导：与实验蠕变数据的比较以及使用水逸度校正外推到自然条件
DOI：
10.1002/2016jb013798
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Ichiko Shimizu
中科院分区：
文献类型：
--
作者：
J. Fukuda;Ichiko Shimizu
我们从理论上推导出石英位错蠕变的流动规律，使用爬升控制位错蠕变模型，并将其与石英塑性变形的实验室数据进行比较。我们假设含氧物质沿着α-石英和β-石英的不同晶轴（//c、R和c）的体积扩散以及H2O的管道扩散是位错攀爬的基本过程。对于体积扩散和管道扩散控制的情况，差应力（σ）和应变速率（ε stec）之间的关系分别记为ε stec σ3Dv和ε stec σ5Dp，其中Dv和Dp是体积扩散和管道扩散的扩散系数。在以前的实验工作中，在使用气体压力介质或固体压力介质变形装置的实验中，水逸度值存在高达1.5个数量级的差异。因此，在理论和流动定律中，我们将水逸度效应包括为修正的指前因子和水逸度项。以前的实验数据主要是在β石英场中获得的，并且与涉及水逸度项的β石英的体积扩散控制位错蠕变模型高度一致。该理论还预测了地壳条件下α-β石英转变的重要影响。在实验压力和温度条件下，管道扩散控制位错蠕变的流变应力高于体积扩散控制蠕变的流变应力。将流动定律外推到自然条件表明，在脆塑性过渡区周围的中地壳低温条件下，管道扩散的贡献可能超过体积扩散。
We theoretically derived flow laws for quartz dislocation creep using climb‐controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen‐bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α‐quartz and β‐quartz, and pipe diffusion of H2O, to be the elementary processes of dislocation climb. The relationships between differential stress (σ) and strain rate ( ε˙ ) are written as ε˙∝σ3Dv and ε˙∝σ5Dp for cases controlled by volume and pipe diffusion, respectively, where Dv and Dp are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water fugacity values in experiments that used either gas‐pressure‐medium or solid‐pressure‐medium deformation apparatus. Therefore, in both the theories and flow laws, we included water fugacity effects as modified preexponential factors and water fugacity terms. Previous experimental data were obtained mainly in the β‐quartz field and are highly consistent with the volume‐diffusion‐controlled dislocation creep models of β‐quartz involving the water fugacity term. The theory also predicts significant effects for the transition of α‐β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe‐diffusion‐controlled dislocation creep is higher than that for volume‐diffusion‐controlled creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low‐temperature conditions of the middle crust around the brittle‐plastic transition zone.