Slab weakening during the olivine to ringwoodite transition in the mantle
Slab weakening during the olivine to ringwoodite transition in the mantle
复制标题
地幔中橄榄石向尖角橄榄石转变过程中板片的弱化
DOI：
10.1038/s41561-019-0523-3
复制
发表时间：
2020
影响因子：
18.3
通讯作者：
J. Girard
中科院分区：
文献类型：
--
作者：
A. Mohiuddin;S. Karato;J. Girard
地幔过渡带俯冲板片的强度影响地幔对流的类型。强烈的变形被观察到，特别是在相对古老的俯冲板在深地幔过渡带。了解板块变形的区域性和深度变化的原因需要深部地幔物质流变学性质的约束。在这里，我们报告的结果，在原位变形实验过程中的橄榄石林伍德石相变，从中我们推断的变形过程中的条件下，冷板深地幔过渡带。我们发现，新转化的细粒ringwoodite变形扩散蠕变，其强度是大大小于粗粒矿物，但随着时间的推移而增加。基于相变动力学和相变过程中粒度演变模型的标度分析表明，冷板坯将由深层过渡区的弱细晶材料和强粗晶材料的混合物制成，而热板坯由于其大粒度而保持强度。我们建议，这种晶粒尺寸的温度依赖性可以解释广泛的变形冷板坯在深过渡区，但相对温暖的板坯有限的变形。在相对较冷的俯冲板，橄榄石可能会转化为细粒，较弱的林伍德石比温暖的板，根据变形实验条件下类似于那些在地幔过渡带和缩放分析。
The strength of subducted slabs in the mantle transition zone influences the style of mantle convection. Intense deformation is observed particularly in relatively old subducted slabs in the deep mantle transition zone. Understanding the cause of this regional and depth variation in slab deformation requires constraint of the rheological properties of deep mantle materials. Here, we report results of in situ deformation experiments during the olivine to ringwoodite phase transformation, from which we infer the deformation process under the conditions of cold slabs deep in the mantle transition zone. We find that newly transformed fine-grained ringwoodite deforms by diffusion creep and that its strength is substantially smaller than that of coarser-grained minerals but increases with time. Scaling analysis, based on a model of transformation kinetics and grain-size evolution during a phase transformation, suggests that a cold slab will be made of a mixture of weak, fine-grained and strong, coarse-grained materials in the deep transition zone, whereas a warm slab remains strong because of its large grain size. We propose that this temperature dependence of grain size may explain extensive deformation of cold slabs in the deep transition zone but limited deformation of relatively warm slabs. In relatively cold subducted slabs, olivine may transform to finer-grained, weaker ringwoodite than in warm slabs, according to deformation experiments under conditions analogous to those in the mantle transition zone and scaling analysis.