The Turkana Depression, a topographically subdued, broadly rifted zone between the elevated East African and Ethiopian plateaus, disrupts the N–S, fault-bounded rift basin morphology that characterizes most of the East African Rift. The unusual breadth of the Turkana Depression leaves unanswered questions about the initiation and evolution of rifting between the Main Ethiopian Rift (MER) and Eastern Rift. Hypotheses explaining the unusually broad, low-lying area include superposed Mesozoic and Cenozoic rifting and a lack of mantle lithospheric thinning and dynamic support. To address these issues, we have carried out the first body-wave tomographic study of the Depression's upper mantle. Seismically derived temperatures at 100 km depth exceed petrological estimates, suggesting the presence of mantle melt, although not as voluminous as the MER, contributes to velocity anomalies. A NW–SE-trending high wavespeed band in southern Ethiopia at 200 km depth is interpreted as refractory Proterozoic lithosphere which has likely influenced the localization of both Mesozoic and Cenozoic rifting. At 100 km depth below the central Depression, a single localized low wavespeed zone is lacking. Only in the northernmost Eastern Rift and southern Lake Turkana is there evidence for focused low wavespeeds resembling the MER, that bifurcate below the Depression and broaden approaching southern Ethiopia further north. These low wavespeeds may be attributed to melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region's multiple rifting phases. Low wavespeeds persist to the mantle transition zone suggesting the Depression may not lack mantle dynamic support in comparison to the two plateaus.

中文翻译：

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图尔卡纳洼地的体波断层成像：对裂谷发育和羽流-岩石圈相互作用的影响

图尔卡纳坳陷是东非和埃塞俄比亚高原之间的一个地形平坦、宽阔的裂谷带，破坏了东非裂谷大部分地区的 N-S、断层边界裂谷盆地形态。图尔卡纳坳陷不寻常的广度留下了关于埃塞俄比亚主裂谷 (MER) 和东部裂谷之间裂谷的开始和演化的悬而未决的问题。解释异常广阔的低洼地区的假设包括叠加的中生代和新生代裂谷以及缺乏地幔岩石圈减薄和动力支持。为了解决这些问题，我们对大萧条的上地幔进行了第一次体波断层扫描研究。100 公里深度的地震得出的温度超过了岩石学估计，这表明存在地幔熔体，尽管不像 MER 那样庞大，导致速度异常。埃塞俄比亚南部的 NW-SE 趋势高波速波段200 公里深度被解释为难熔的元古代岩石圈，这可能影响了中生代和新生代裂谷的定位。在中央坳陷以下 100 公里深处，缺乏单一的局部低波速区。只有在最北端的东部裂谷和南部图尔卡纳湖才有证据表明类似 MER 的聚焦低波速在低洼下方分叉并扩大到更北的埃塞俄比亚南部。这些低波速可能归因于熔体侵入地幔岩石圈或由该地区的多个裂谷相引起的岩石圈薄点下方的软流圈物质。低波速持续到地幔过渡带，表明与两个高原相比，坳陷可能不缺乏地幔动力支持。