Ultralow velocity zone and deep mantle flow beneath the Himalayas linked to subducted slab
Ultralow velocity zone and deep mantle flow beneath the Himalayas linked to subducted slab
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DOI：
10.1038/s41561-024-01386-5
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发表时间：
2024-02
影响因子：
18.3
通讯作者：
Jonathan Wolf;Maureen D. Long;Daniel A. Frost
中科院分区：
文献类型：
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作者：
Jonathan Wolf;Maureen D. Long;Daniel A. Frost
超低速区的起源仍然知之甚少，超低速区是在核幔边界附近发现的具有极低地震速度的小规模结构。一种假设是，它们是积极参与地幔对流的移动特征，但对超低速区域附近的地幔流知之甚少，也难以推断。尽管深部地幔各向异性观测可用于推断地幔流动模式，但超低速区结构通常不与这些观测联合检查。在这里，我们提供了来自地震波的证据，这些地震波对喜马拉雅山下方的最低地幔进行了采样，发现了超低速区和与地幔流相关的地震各向异性的邻近区域。通过使用全球波场模拟对真实的矿物物理场景进行建模，我们表明所识别的地震各向异性与东北-西南方向的水平剪切一致。根据周围地幔结构的层析成像数据，我们认为这种西南流可能与撞击核幔边界的俯冲板片残余物有关。探测到的超低速带位于该各向异性区域的西南边缘，因此可能受到周围地区强烈地幔变形的影响。
The origins of ultralow velocity zones, small-scale structures with extremely low seismic velocities found near the core–mantle boundary, remain poorly understood. One hypothesis is that they are mobile features that actively participate in mantle convection, but mantle flow adjacent to ultralow velocity zones is poorly understood and difficult to infer. Although deep mantle anisotropy observations can be used to infer mantle flow patterns, ultralow velocity zone structures are often not examined jointly with these observations. Here we present evidence from seismic waves that sample the lowermost mantle beneath the Himalayas for both an ultralow velocity zone and an adjacent region of seismic anisotropy associated with mantle flow. By modelling realistic mineral physics scenarios using global wavefield simulations, we show that the identified seismic anisotropy is consistent with horizontal shearing orientated northeast–southwest. Based on tomographic data of the surrounding mantle structure, we suggest that this southwestward flow is potentially linked to the remnants of the subducted slab impinging on the core–mantle boundary. The detected ultralow velocity zone is located at the southwestern edge of this anisotropic region, and therefore potentially affected by strong mantle deformation in the surrounding area.