Constraining Mantle Viscosity Structure From a Statistical Analysis of Slab Stagnation Events
Constraining Mantle Viscosity Structure From a Statistical Analysis of Slab Stagnation Events
复制标题
DOI：
10.1029/2020gc009286
复制
发表时间：
2020-10
期刊：
影响因子：
3.7
通讯作者：
Yongming Wang;Mingming Li
中科院分区：
文献类型：
--
作者：
Yongming Wang;Mingming Li
地幔的粘度结构，甚至一维径向粘度剖面，仍然没有得到很好的约束。俯冲板片的动力学受到地幔粘性结构的强烈影响，并且可以用来约束地幔的粘性结构。在这里，我们执行完全动态、自洽的地幔对流模型来研究深部地幔中俯冲板块的动力学。我们使用统计分析方法来量化地幔粘度的深度依赖性如何影响平躺板片的深度分布。我们发现，对于在 660 km 深度处粘度增加的情况，无论是急剧还是逐渐增加，平躺板片优先出现在该深度之上，并且重要的是，高达约 30% 的俯冲板片先前在该深度平坦化，后来沉入深部下地幔并保持平躺形态。在这些情况下，在 1,000 公里深度处出现平躺板片的频率（或出现概率）与在 1,000 公里深度处发生粘度跳跃的情况类似。因此，要解释地球约 1,000 公里深度处存在平坦板块，不需要在此深度出现粘度跳跃。相比之下，仅仅发生在~1000公里深度的粘度跳跃导致在~700-900公里深度的最上层下地幔中缺乏平坦的板片，并且与地震观测不一致。地球最上层下地幔中存在平坦的板状材料，需要在 660 公里深度处增加粘度。
The viscosity structure of Earth's mantle, even the 1‐D radial viscosity profile, remains not well constrained. The dynamics of the subducting slabs is strongly affected by, and can be used to constrain, the viscosity structure of the mantle. Here, we perform fully dynamic, self‐consistent mantle convection models to study the dynamics of subducted slabs in the deep mantle. We use a statistical analysis approach to quantify how the depth distribution of flat‐lying slabs is affected by the depth‐dependence of mantle viscosity. We find that, for cases in which the viscosity increases at 660 km depth, whether sharply or gradually, flat‐lying slabs preferentially occur above this depth, and importantly, up to ∼30% of the subducted slabs previously flatted at this depth later sink to the deep lower mantle and maintain a flat‐lying morphology. The frequency of (or the probability to have) flat‐lying slabs at ∼1,000 km depth in these cases is similar to cases in which the viscosity jump occurs at 1,000 km depth. Therefore, to explain the presence of flat‐lying slabs at ∼1,000 km depth for the Earth does not require a viscosity jump at this depth. In contrast, a viscosity jump merely occurring at ∼1,000 km depth causes a lack of flat‐lying slabs in the uppermost lower mantle at ∼700–900 km depth and is inconsistent with seismic observations. The presence of flat‐lying slab materials in the Earth's uppermost lower mantle requires a viscosity increase at 660 km depth.