Grain boundary diffusion creep of olivine: 2. Solidus effects and consequences for the viscosity of the oceanic upper mantle
Grain boundary diffusion creep of olivine: 2. Solidus effects and consequences for the viscosity of the oceanic upper mantle
复制标题
橄榄石的晶界扩散蠕变：2. 固相线效应及其对大洋上地幔粘度的影响
DOI：
10.1029/2020jb019416
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
T. Hiraga
中科院分区：
文献类型：
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作者：
K. Yabe;T. Hiraga
我们对细粒（~1 μm）含铁橄榄石（Mg1.8Fe0.2SiO4）聚集体进行了单大气单轴压缩实验，这些聚集体被CaO ± Al 2 O3掺杂。我们确定了低应力下的幂律界面控制蠕变和高应力下的晶界扩散蠕变，它们是相互耦合的，即顺序过程。我们建立了未掺杂橄榄石的界面控制蠕变和扩散蠕变的本构方程，并使用组合速率方程作为参考来研究掺杂对蠕变速率的影响。发现Ca和Al在一定温度以上提高界面控制蠕变和扩散蠕变的速率，并且这种效果随着温度的升高而变得显著。我们将速率提高归因于在近固相线条件下由掺杂剂的晶界偏析促进的晶界无序。的增强被很好地描述在相对于参考蠕变状态的样品固相线温度和一个额外的活化能。
We conducted one‐atmosphere uniaxial compression experiments on fine‐grained (~1 μm) Fe‐bearing olivine (Mg1.8Fe0.2SiO4) aggregates that were variably doped with CaO ± Al2O3. We identified power‐law interface‐controlled creep at low stresses and grain‐boundary diffusion creep at high stresses, which operate as mutually coupled, that is, sequential processes. We established constitutive equations for interface‐controlled creep and diffusion creep of undoped olivine and used the combined rate equation as a reference to examine the effect of doping on creep rates. Ca and Al were found to enhance rates of both interface‐controlled creep and diffusion creep above certain temperatures, and this effect becomes significant with increasing temperature. We attribute the rate enhancements to grain‐boundary disordering promoted by grain‐boundary segregation of the dopants at near‐solidus conditions. The enhancements are well described in relation to the sample solidus temperature and an additional activation energy relative to that of the reference creep state.