Constraining mantle flow with seismic and geodynamic data: A joint approach
Constraining mantle flow with seismic and geodynamic data: A joint approach
复制标题
用地震和地球动力学数据约束地幔流：联合方法
DOI：
10.1016/j.epsl.2006.04.003
复制
发表时间：
2006
影响因子：
5.3
通讯作者：
S. Grand
中科院分区：
文献类型：
--
作者：
N. Simmons;A. Forte;S. Grand
了解地幔中对流的类型对于了解地球内部的热演化和化学演化以及驱动板块构造的力量至关重要。基于三维地震层析重建的地幔对流模型有可能提供对地幔流动最直接的约束。近年来，地球深部结构的地震成像取得了很大的进展，但是，它还没有能够达成共识的地幔对流的性质。基于层析成像结果的地幔流动模型得出了各种不同的结论，主要是因为地震层析成像模型固有的非唯一性和不同的分辨率，以及直接从地震图像确定流动的困难。在这里，我们解决这个困难，同时反演全球地震和对流相关的数据集。地震数据由全球分布的剪切体波走时组成，包括多反射S波、浅转向三重相位以及岩心反射和穿过岩心的相位（SKS和SKKS）。对流相关的数据集包括全球自由空气重力，构造板块的分歧，以及核幔边界的过度椭圆率。此外，对流相关的约束动力表面地形的基础上，最近的全球地壳非均匀性模型估计。这些与对流有关的观测量与地幔密度异常有关，通过瞬时地幔流计算，并通过优化的密度-速度标度关系与地震数据联系起来。同时反演使我们能够测试各种地幔流动的假设直接对地震和对流相结合的数据集，而不是考虑流动预测的基础上，地震派生的3-D地幔模型。在这项研究中，我们测试了四种不同的地幔流假说，包括全地幔流和模型，在670公里，1200公里和1800公里的深度不可穿透的流动边界。这一假设检验表明，当考虑到全地幔流动情景时，全球地震和地球动力学综合数据集的一致性最好。对流模型与限制性流动边界内的下地幔提供明显较差的适合这些组合的数据集，提供证据表明，地幔流动没有永久性障碍的边界考虑。
Understanding the style of convective flow occurring in the mantle is essential to understand the thermal and chemical evolution of Earth's interior as well as the forces driving plate tectonics. Models of mantle convection based on three-dimensional (3-D) seismic tomographic reconstructions have the potential to provide the most direct constraints on mantle flow. Seismic imaging of deep Earth structure has made great advances in recent years; however, it has not been possible to reach a consensus on the nature of convection in the mantle. Models of mantle flow based on tomography results have yielded variable conclusions largely because of the inherent non-uniqueness and differing degrees of resolution of seismic tomography models as well as the difficulty in determining flow directly from seismic images. Here we address this difficulty by simultaneously inverting global seismic and convection-related data sets. The seismic data consist of globally distributed shear body wave travel times including multi-bounce S-waves, shallow-turning triplicated phases, as well as core reflections and phases traversing the core (SKS and SKKS). Convection-related data sets include global free air gravity, tectonic plate divergence, and excess ellipticity of the core–mantle boundary. In addition, the convection-related constraint on dynamic surface topography is estimated on the basis of a recent global model of crustal heterogeneity. These convection-related observables are related to mantle density anomalies through instantaneous mantle flow calculations and linked to the seismic data via optimized density–velocity scaling relationships. Simultaneous inversion allows us to test various mantle flow hypotheses directly against the combined seismic and convection data sets, rather than considering flow predictions based solely on a seismically derived 3-D mantle model. In this study, we test four different mantle flow hypotheses, including whole-mantle flow and models with impenetrable flow boundaries at depths of 670 km, 1200 km, and 1800 km. This hypothesis testing shows that the combined global seismic and geodynamic data sets are best reconciled when a whole-mantle flow scenario is considered. Convection models with restrictive flow boundaries within the lower mantle provide distinctly poorer fits to these combined data sets providing evidence that the mantle flows without permanent hindrance at the boundaries considered.