Mantle transition zone structure and upper mantle S velocity variations beneath Ethiopia: Evidence for a broad, deep‐seated thermal anomaly
Mantle transition zone structure and upper mantle S velocity variations beneath Ethiopia: Evidence for a broad, deep‐seated thermal anomaly
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埃塞俄比亚下方的地幔过渡带结构和上地幔S速度变化：广泛、深层热异常的证据
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发表时间：
2006
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通讯作者：
G. Stuart
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作者：
M. Benoit;A. Nyblade;T. J. Owens;G. Stuart
埃塞俄比亚一直受到广泛的新生代火山活动，裂谷，并与阿法尔热点隆起。热点构造作用被认为是地幔中一次或多次热隆起的结果，如热柱和超热柱的形成。我们调查热点的起源成像的S波速度结构的上地幔埃塞俄比亚下使用旅行时层析成像和检查救济过渡区不连续性使用接收器函数堆栈。断层图像显示了一个细长的低速区域，该区域宽（>500 km），并深入到上地幔（>400 km）。异常与上地幔的阿法尔凹陷和埃塞俄比亚主裂谷对齐，但其中心随深度向西移动。410公里长的不连续面没有得到很好的成像，但660公里长的不连续面在埃塞俄比亚大部分地区下方比正常深度浅20-30公里，但在吉布提和埃塞俄比亚高原西北边缘下方处于正常深度。层析成像结果与660 km浅界面相结合表明，上地幔温度升高了300 K，热异常宽（>500 km），深度≥660 km。热异常的尺寸与热羽流的起始不一致，但与来自下地幔的过量热量通量一致。如此广泛的热上升流可能是在南部非洲下地幔中发现的非洲超级地幔柱的一部分。
Ethiopia has been subjected to widespread Cenozoic volcanism, rifting, and uplift associated with the Afar hot spot. The hot spot tectonism has been attributed to one or more thermal upwellings in the mantle, for example, starting thermal plumes and superplumes. We investigate the origin of the hot spot by imaging the S wave velocity structure of the upper mantle beneath Ethiopia using travel time tomography and by examining relief on transition zone discontinuities using receiver function stacks. The tomographic images reveal an elongated low‐velocity region that is wide (>500 km) and extends deep into the upper mantle (>400 km). The anomaly is aligned with the Afar Depression and Main Ethiopian Rift in the uppermost mantle, but its center shifts westward with depth. The 410 km discontinuity is not well imaged, but the 660 km discontinuity is shallower than normal by ∼20–30 km beneath most of Ethiopia, but it is at a normal depth beneath Djibouti and the northwestern edge of the Ethiopian Plateau. The tomographic results combined with a shallow 660 km discontinuity indicate that upper mantle temperatures are elevated by ∼300 K and that the thermal anomaly is broad (>500 km wide) and extends to depths ≥660 km. The dimensions of the thermal anomaly are not consistent with a starting thermal plume but are consistent with a flux of excess heat coming from the lower mantle. Such a broad thermal upwelling could be part of the African Superplume found in the lower mantle beneath southern Africa.