Initiation of the western branch of the East African Rift coeval with the eastern branch
Initiation of the western branch of the East African Rift coeval with the eastern branch
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DOI：
10.1038/ngeo1432
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发表时间：
2012-04
影响因子：
18.3
通讯作者：
E. Roberts;N. Stevens;P. O’Connor;P. Dirks;M. Gottfried;W. Clyde;R. Armstrong;A. Kemp;S. Hemming
中科院分区：
文献类型：
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作者：
E. Roberts;N. Stevens;P. O’Connor;P. Dirks;M. Gottfried;W. Clyde;R. Armstrong;A. Kemp;S. Hemming
东非裂谷系统横穿异常高海拔的埃塞俄比亚和东非高原，这两个高原共同构成了6000公里长的非洲超级水井结构的一部分。据推测，裂谷作用是在东非地下开始的地幔热柱活动的结果。地幔活动引起了与非洲新生代气候变化和动物群演化有关的地形抬升。传统上，裂谷被解释为由两个截然不同的部分组成：一个较老的、火山活跃的东部分支和一个较年轻、火山活动较少的西部分支。这里，我们证明了西支裂谷的开始比之前认为的要早1400多万年，与东支同时开始。我们结合碎屑锆石年代学、火山岩和磁性地层学，以及对坦桑尼亚鲁克瓦裂谷盆地沉积岩中记录的过去河流流量的分析，来限制西支这一部分的裂谷作用、岩浆作用和水系发育的时间。我们发现，与裂谷相关的火山活动和湖泊发育在大约2500万年前( )就已经开始了。在这些事件之前，山前发育和河流排水逆转，我们认为记录了由非洲超强井引起的地形抬升的开始。我们的结论是，东非的隆起比以前认识到的更为广泛和同步。
The East African Rift System transects the anomalously high-elevation Ethiopian and East African plateaux that together form part of the 6,000-km-long African superswell structure. Rifting putatively developed as a result of mantle plume activity that initiated under eastern Africa. The mantle activity has caused topographic uplift that has been connected to African Cenozoic climate change and faunal evolution. The rift is traditionally interpreted to be composed of two distinct segments: an older, volcanically active eastern branch and a younger, less volcanic western branch. Here, we show that initiation of rifting in the western branch began more than 14 million years earlier than previously thought, contemporaneously with the eastern branch. We use a combination of detrital zircon geochronology, tephro- and magnetostratigraphy, along with analyses of past river flow recorded in sedimentary rocks from the Rukwa Rift Basin, Tanzania, to constrain the timing of rifting, magmatism and drainage development in this part of the western branch. We find that rift-related volcanism and lake development had begun by about 25 million years ago. These events were preceded by pediment development and a fluvial drainage reversal that we suggest records the onset of topographic uplift caused by the African superswell. We conclude that uplift of eastern Africa was more widespread and synchronous than previously recognized.