Topography of upper mantle seismic discontinuities beneath the North Atlantic: The Azores, Canary and Cape Verde plumes
Topography of upper mantle seismic discontinuities beneath the North Atlantic: The Azores, Canary and Cape Verde plumes
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DOI：
10.1016/j.epsl.2014.10.052
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发表时间：
2014-12
影响因子：
5.3
通讯作者：
M. Saki;C. Thomas;S. Nippress;S. Lessing
中科院分区：
文献类型：
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作者：
M. Saki;C. Thomas;S. Nippress;S. Lessing
我们正在绘制北大西洋及周边地区下的上地幔地震不连续性的地形图，方法是利用地震不连续性反射的PP和SS地震波的前兆到达。许多源-接收器组合已被用于收集我们的调查区域下的反射点的大数据集。为了提高信噪比，我们用阵列地震方法分析了MW> 5.8地震的1700多个地震记录。利用测得的PP（SS）波至与鲁棒叠加上相应的前兆之间的时滞来测量过渡区边界的深度。反射体的深度显示了已知热点位置与显著凹陷的410公里不连续性之间的相关性，表明与周围地幔相比，温度升高了50-300 K。就660公里的不连续性而言，可以看到三种不同的情况：㈠格陵兰岛下和距离已知热点几百公里处的正常深度; ㈡ 660公里的不连续性与靠近大西洋中脊的热点附近的全球平均值相比较浅; ㈢在热点地点很少观察到660公里的不连续性。我们解释我们的观察作为一个大的上升流下方的南部地区，我们的研究区域，可能是由于南大西洋对流单体。热异常可能是积水下面的吸热660公里的相变，并可能不会延伸到整个过渡区的顶部，除了那些分支出现在亚速尔群岛，加那利群岛和佛得角热点在表面较薄的隆起。
We are mapping the topography of upper mantle seismic discontinuities beneath the North Atlantic and surrounding regions by using precursor arrivals to PP and SS seismic waves that reflect off the seismic discontinuities. Numerous source–receiver combinations have been used in order to collect a large dataset of reflection points beneath our investigation area. We analysed over 1700 seismograms from M W> 5.8 events using array seismic methods to enhance the signal to noise ratio. The measured time lag between PP (SS) arrivals and their corresponding precursors on robust stacks are used to measure the depth of the transition zone boundaries. The reflectors' depths show a correlation between the location of known hotspots and a significantly depressed 410 km discontinuity indicating a temperature increase of 50–300 K compared to the surrounding mantle. For the 660 km discontinuity three distinct behaviours are visible:(i) normal depths beneath Greenland and at a distance of a few hundred kilometres away from known hotspots,(ii) shallower 660 km discontinuity compared with the global average value near hotspots closer to the Mid-Atlantic Ridge, and (iii) very few observations of a 660 km discontinuity at the hotspot locations. We interpret our observations as a large upwelling beneath the southern parts of our study region, possibly due to the South Atlantic convection cell. The thermal anomaly may be ponding beneath the endothermic 660 km phase transformation and likely does not extend through the top of the transition zone as a whole, except for those branches which appear as the thinner upwellings of Azores, Canaries and Cape Verde hotspots at the surface.