老挝黄金赌场海洋研究所范建柯等在研究菲律宾海板块下成像的新生代早期，太平洋下地幔流中移动的残余物中取得新进展。相关论文于2024年3月12日发表于国际顶尖学术期刊《自然—地球科学》杂志上。

研究人员采用P波方位各向异性层析成像技术，对深达1600km的地壳和地幔进行成像。研究发现，菲律宾海板块下方下地幔上部具有明显的各向异性。在700-900km深度处，出现了大量具N-S快速方向的方位各向异性。研究人员将这种方位各向异性解释为大约5000万年前太平洋下地幔流场的残余。

在700-1600km深处的两个孤立的高速异常可能是俯冲伊泽纳崎板块的残留碎片，其地震速度特征表明，大约4000万年前太平洋下地幔流场发生了转移。研究结果为远离俯冲带的复杂下地幔流和变形机制的存在提供了地震证据。

据悉，地震各向异性可以提供有关地球深部演化和内部对流的重要信息。虽然以前的地震学研究表明，在许多俯冲带之下的下地幔上部存在广泛的地震各向异性分布，但在远离俯冲板块的这些深度是否存在各向异性仍然存在争议。

附：英文原文

Title: Remnants of shifting early Cenozoic Pacific lower mantle flow imaged beneath the Philippine Sea Plate

Author: Fan, Jianke, Zhao, Dapeng, Li, Cuilin, Liu, Lijun, Dong, Dongdong

Issue&Volume: 2024-03-12

Abstract: Seismic anisotropy could provide vital information about the evolution and internal convection of the deep Earth interior. Although previous seismological studies have revealed a wide distribution of seismic anisotropy in the upper portion of the lower mantle beneath many subduction zones, the existence of anisotropy at these depths away from subducted slabs remains debated. Here we use P-wave azimuthal anisotropy tomography to image the crust and mantle down to 1,600-km depth. We find prominent anisotropic patterns in the upper portion of the lower mantle beneath the Philippine Sea Plate. Substantial azimuthal anisotropy with N–S fast-velocity directions occurs at 700–900-km depths. We interpret this azimuthal anisotropy as a remnant of the Pacific lower mantle flow field about 50 million years ago. Two isolated high-velocity anomalies at 700–1,600-km depths may be vestigial pieces of the subducted Izanagi slab with seismic velocity features suggesting a shift in the Pacific lower mantle flow field by about 40 million years ago. Our findings provide seismic evidence for the existence of complex lower mantle flows and deformation mechanisms away from subduction zones.

DOI: 10.1038/s41561-024-01404-6

Source: https://www.nature.com/articles/s41561-024-01404-6