Formation of Horizontally Deflected Slabs in the Mantle Transition Zone Caused by Spinel‐to‐Post‐Spinel Phase Transition, Its Associated Grainsize Reduction Effects, and Trench Retreat
Formation of Horizontally Deflected Slabs in the Mantle Transition Zone Caused by Spinel‐to‐Post‐Spinel Phase Transition, Its Associated Grainsize Reduction Effects, and Trench Retreat
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DOI：
10.1029/2021gl093679
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发表时间：
2021-07
影响因子：
5.2
通讯作者：
W. Mao;S. Zhong
中科院分区：
文献类型：
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作者：
W. Mao;S. Zhong
地震观测表明，在许多俯冲带的地幔过渡带中存在俯冲板片的堆积。通过系统地进行二维数值实验，我们证明了尖晶石到后尖晶石相变下方的弱层或区域导致地幔过渡区中的水平偏转（停滞）板状结构，这与最近的三维全球地幔对流模型研究一致。海沟后退速度、克拉珀龙斜坡以及下地幔与地幔过渡带之间的粘度差异也影响水平偏转板片的形成。通过考虑晶粒尺寸依赖的粘度和晶粒尺寸的演化板块经历相变在下地幔，我们的模型与动态生成的弱区相边界下的几何形状和粘度降低的弱区的强烈影响的晶粒生长速率。较小的晶粒生长速率导致更厚和更宽的弱区，这促进了偏转板坯的形成。
Seismic observations indicate accumulation of subducted slabs in the mantle transition zone in many subduction zones. By systematically conducting 2‐D numerical experiments, we demonstrate that a weak layer or zone beneath the spinel‐to‐post‐spinel phase transition leads to horizontally deflected (stagnant) slab structures in the mantle transition zone, which is consistent with recent studies of 3‐D global mantle convection models. Trench retreat velocity, Clapeyron slope and the viscosity contrast between the lower mantle and mantle transition zone also affect horizontally deflected slab formation. By considering grain size dependent viscosity and grainsize evolution for slabs going through the phase change in the lower mantle, our models with a dynamically generated weak zone beneath the phase boundary indicate that the geometry and viscosity reduction of the weak zone is strongly affected by grain growth rate. A smaller grain growth rate results in a thicker and wider weak zone that promotes deflected slab formation.