Crustal Velocity Structure Across the Main Ethiopian Rift
Crustal Velocity Structure Across the Main Ethiopian Rift
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DOI：
10.1111/j.1365-246x.2005.02710.x
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发表时间：
2003-12
期刊：
影响因子：
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通讯作者：
G. Mackenzie;H. Thybo;P. Maguire;T. Mammo;M. A. Khan
中科院分区：
文献类型：
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作者：
G. Mackenzie;H. Thybo;P. Maguire;T. Mammo;M. A. Khan
摘要我们提出了最近获得的广角地震反射/折射剖面横跨埃塞俄比亚主裂谷的速度建模的结果。这些模型显示出大陆型地壳，裂谷两侧具有显著的不对称性。在整个地区建立了2至5公里厚的沉积和火山序列模型。这是下B一个40至45公里厚的地壳与c。西部高原下15公里厚的高速最低地壳层。东侧没有这一层，那里的地壳在沉积物之下有35公里厚。我们解释这一层的底镀材料与该地区的渐新世洪水玄武岩可能随后增加最近的岩浆事件。轻微的地壳变薄的裂谷下，其中Pn速度表明存在热地幔岩石含有部分熔融。在裂谷轴之下，上地壳层的速度比裂谷之外高5 - 10%，我们解释这是由于镁铁质侵入体造成的，这些侵入体可能与裂谷中观察到的岩浆中心有关。地震反射率的变化表明，在裂谷下方的下地壳存在分层，可能表明存在岩床，以及在拟议的底侵体中存在一些分层。
SUMMARY We present the results of velocity modelling of a recently acquired wide-angle seismic reflection/refraction profile across the Main Ethiopian Rift. The models show a continental type of crust with significant asymmetry between the two sides of the rift. A 2- to 5-km-thick layer of sedimentary and volcanic sequences is modelled across the entire region. This is underlain b ya 40- to 45-km-thick crust with a c. 15-km-thick high-velocity lowest crustal layer beneath the western plateau. This layer is absent from the eastern side, where the crust is 35 km thick beneath the sediments. We interpret this layer as underplated material associated with the Oligocene flood basalts of the region with possible subsequent addition by recent magmatic events. Slight crustal thinning is observed beneath the rift, where Pn velocities indicate the presence of hot mantle rocks containing partial melt. Beneath the rift axis, the velocities of the upper crustal layers are 5‐10 per cent higher than outside the rift, which we interpret as resulting from mafic intrusions that can be associated with magmatic centres observed in the rift valley. Variations in seismic reflectivity suggest the presence of layering in the lower crust beneath the rift, possibly indicating the presence of sills, as well as some layering in the proposed underplated body.