美国耶鲁大学Wolf, Jonathan团队在研究与俯冲板块有关的喜马拉雅山下超低速带和深部地幔流中取得新进展。这一研究成果于2024年2月26日发表在国际顶尖学术期刊《自然—地球科学》上。

研究人员提供了来自喜马拉雅山下最下层地幔的地震波样本的证据，包括与地幔流动相关的超低速带和相邻地震各向异性区域。研究发现，通过使用全球波场模拟的真实矿物物理场景，识别的地震各向异性与东北—西南方向的水平剪切相一致。

基于周围地幔结构的层析成像数据，团队研究人员认为这种向西南的流动可能与俯冲板块的残余物撞击核幔边界有关。探测到的超低速带位于该各向异性区的西南边缘，因此可能受到周边地区强地幔变形的影响。

据了解，研究人员对在地核—地幔边界附近发现的超低速度带（地震速度极低的小规模结构）的起源知之甚少。一种假设是，它们具积极参与地幔对流的活动特征，但人们对超低速带附近的地幔流动知之甚少且难以推断。虽然深部地幔各向异性观测可以用来推断地幔流动模式，但超低速带结构往往不能与这些观测相结合。

附：英文原文

Title: Ultralow velocity zone and deep mantle flow beneath the Himalayas linked to subducted slab

Author: Wolf, Jonathan, Long, Maureen D., Frost, Daniel A.

Issue&Volume: 2024-02-26

Abstract: 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.

DOI: 10.1038/s41561-024-01386-5

Source: https://www.nature.com/articles/s41561-024-01386-5