High-resolution full waveform seismic tomography of the Earth’s mantle beneath the south and central Atlantic Ocean brings into focus a series of asthenospheric low shear velocity channels, or “fingers” on both sides of the southern and central mid-Atlantic ridge (MAR), elongated in the direction of absolute plate motion with a spacing of ∼ 1,800 to 2,000 km, and associated with bands of shallower residual seafloor depth anomalies that suggest channeled flow over thousands of kilometers. Each of the three most clearly resolved fingers on the African side of the MAR corresponds to a separate group of whole mantle plumes rooted in distinct patches at the core–mantle boundary, feeding hotspots, and volcanic lines with distinct isotopic signatures. Plumes of a given group appear to merge at the top of the lower mantle before separating again, suggesting interaction of deep mantle flow with a more vigorous mesoscale circulation in the upper mantle. The corresponding hotspots are generally offset from the location of the deep mantle plume roots. The distinct isotopic signatures of these hotspot groups are also detected in the mid-ocean ridge basalts at the location where the fingers meet the ridge. Meanwhile, at least some of the variability within each plume group could originate in the upper mantle and extended transition zone where plumes in a given group appear to merge and pond. This study also adds to mounting evidence that the African large low shear velocity province is not a uniform, unbroken pile of dense material rising high above the core–mantle boundary, but rather a collection of mantle plumes rooted in patches of distinct composition.

中文翻译：

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深地幔羽流为大西洋中部和南部下方的软流圈指周期性排列提供食物


大西洋南部和中部地幔的高分辨率全波形地震层析成像使一系列流流层低剪切速度通道或位于大西洋中部中脊 （MAR） 南部和中部两侧的“手指”成为焦点，沿绝对板块运动方向拉长，间距约为 1,800 至 2,000 公里， 并与较浅的残余海底深度异常带有关，这些异常表明数千公里的通道流。MAR 非洲一侧的三个最清晰分辨的指状体中的每一个都对应于一组单独的整个地幔羽流，这些羽流植根于核心-地幔边界的不同斑块、供食热点和具有不同同位素特征的火山线。给定组的羽流似乎在下地幔的顶部合并，然后再次分离，这表明深地幔流与上地幔中更活跃的中尺度环流相互作用。相应的热点通常与深地幔羽流根的位置偏移。这些热点群的不同同位素特征也在洋中脊玄武岩中检测到，位于手指与山脊相交的位置。同时，每个羽流组内的至少一些变化可能源于上地幔和扩展的过渡带，其中给定组中的羽流似乎会合并和聚集。这项研究还增加了越来越多的证据，表明非洲大型低剪切速度省不是一堆均匀、不间断的致密物质，高高耸立在地核-地幔边界之上，而是一组植根于不同成分的斑块中的地幔羽流。