Asthenospheric low-velocity zone consistent with globally prevalent partial melting
Asthenospheric low-velocity zone consistent with globally prevalent partial melting
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DOI：
10.1038/s41561-022-01116-9
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发表时间：
2023-02-06
影响因子：
18.3
通讯作者：
Hirth, Greg
中科院分区：
文献类型：
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作者：
Hua, Junlin;Fischer, Karen M.;Hirth, Greg
软流圈在现今的板块构造中起着重要的作用，因为它的低粘度控制着它下面的地幔中的对流如何在上面的地球表面表达。软流圈的起源，包括部分熔融在降低其粘度和促进变形方面的作用，仍然不清楚。在这里，我们分析了全球分布的地震台站的接收功能数据，以成像软流圈低地震速度区的下游。我们提出了全球广泛的证据，积极的地震速度梯度在深度类似于150公里，这是一个特别低的速度区的软流圈内的基础。这种边界最常在上地幔温度升高的地区被探测到，最好被模拟为部分熔融层的基础。边界的存在没有表现出相关性与径向地震各向异性，这代表累积地幔应变，表明推断的部分熔融大规模的软流圈粘度没有实质性的影响。这些结果表明，软流层中存在着全球广泛的部分熔融区，但软流层的低粘度主要受压力和温度随深度逐渐变化的控制。软流层中的部分熔融低地震速度区在全球普遍存在，但部分熔融并不是控制低软流层粘度的主要因素，根据对穿过地幔的地震波的分析，
The asthenosphere plays a fundamental role in present-day plate tectonics as its low viscosity controls how convection in the mantle below it is expressed at the Earth's surface above. The origin of the asthenosphere, including the role of partial melting in reducing its viscosity and facilitating deformation, remains unclear. Here we analysed receiver-function data from globally distributed seismic stations to image the lower reaches of the asthenospheric low-seismic-velocity zone. We present globally widespread evidence for a positive seismic-velocity gradient at depths of similar to 150 km, which represents the base of a particularly low-velocity zone within the asthenosphere. This boundary is most commonly detected in regions with elevated upper-mantle temperatures and is best modelled as the base of a partially molten layer. The presence of the boundary showed no correlation with radial seismic anisotropy, which represents accumulated mantle strain, indicating that the inferred partial melt has no substantial effect on the large-scale viscosity of the asthenosphere. These results imply the presence of a globally extensive, partially molten zone embedded within the asthenosphere, but that low asthenospheric viscosity is controlled primarily by gradual pressure and temperature variations with depth.A partially molten low-seismic-velocity zone in the asthenosphere is globally prevalent, but partial melting is not the primary control of low asthenospheric viscosity, according to analysis of seismic waves travelling through the mantle.