Ubiquitous lower-mantle anisotropy beneath subduction zones
Ubiquitous lower-mantle anisotropy beneath subduction zones
复制标题
DOI：
10.1038/s41561-019-0325-7
复制
发表时间：
2019-04-01
影响因子：
18.3
通讯作者：
Schardong, Lewis
中科院分区：
文献类型：
--
作者：
Ferreira, Ana M. G.;Faccenda, Manuele;Schardong, Lewis
地震各向异性为绘制地幔流动轨迹和了解地球演化提供了关键信息。尽管各向异性在最上地幔中的存在已得到证实，但在过渡带和最上下地幔中各向异性的存在和性质仍存在争议。在这里，我们使用基于对该区域敏感的大数据集的三维全球地震层析成像图像来显示俯冲带下地幔中普遍存在的各向异性。而在660公里以上的地震不连续板条上，快SV异常高达3%左右，而在下地幔，约2%的快SH异常在板条附近持续到约1000-1200公里。这些观察结果与俯冲板片变形的三维数值模型以及高应力区位错蠕变过程中产生的桥辉石晶格择优取向是一致的。这项研究提供了位错蠕变可能在地球下地幔中活跃的证据，为地球深处这一关键但难以接近的组成部分的变形性质提供了新的限制。
Seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet. While the presence of anisotropy in the uppermost mantle is well established, the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated. Here we use three-dimensional global seismic tomography images based on a large dataset that is sensitive to this region to show the ubiquitous presence of anisotropy in the lower mantle beneath subduction zones. Whereas above the 660 km seismic discontinuity slabs are associated with fast SV anomalies up to about 3%, in the lower mantle fast SH anomalies of about 2% persist near slabs down to about 1,000-1,200 km. These observations are consistent with 3D numerical models of deformation from subducting slabs and the associated lattice-preferred orientation of bridgmanite produced in the dislocation creep regime in areas subjected to high stresses. This study provides evidence that dislocation creep may be active in the Earth's lower mantle, providing new constraints on the debated nature of deformation in this key, but inaccessible, component of the deep Earth.