Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015, USA.
Science. 2012 Mar 23;335(6075):1480-3. doi: 10.1126/science.1215433.
The lithosphere-asthenosphere boundary (LAB) beneath ocean basins separates the upper thermal boundary layer of rigid, conductively cooling plates from the underlying ductile, convecting mantle. The origin of a seismic discontinuity associated with this interface, known as the Gutenberg discontinuity (G), remains enigmatic. High-frequency SS precursors sampling below the Pacific plate intermittently detect the G as a sharp, negative velocity contrast at 40- to 75-kilometer depth. These observations lie near the depth of the LAB in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base. I propose that the G reflectivity is regionally enhanced by dynamical processes that produce melt, including hot mantle upwellings, small-scale convection, and fluid release during subduction.
洋底下的岩石圈-软流圈边界（LAB）将刚性、传导冷却板块的上热边界层与下方韧性、对流地幔隔开。与该界面相关的地震不连续面的起源，即古登堡不连续面（G），仍然是个谜。在太平洋板块下方采样的高频 SS 前震间歇性地探测到 G，其在 40-75 公里的深度呈现出明显的负速度对比。这些观测结果位于与近期地表火山活动和地幔熔体产生相关的 LAB 深度附近，与位于岩石圈底部的间歇性软流圈部分熔融层一致。我提出，产生熔体的动力学过程会局部增强 G 的反射率，包括热地幔上涌、小规模对流和俯冲过程中的流体释放。
