How does the Earth's crust grow at divergent plate boundaries? A unique opportunity in Afar, Ethiopia.

非洲大陆正沿着东非裂谷慢慢分裂，东非裂谷是一系列3000公里长的深盆地和两侧山脉。这一过程可能最终导致新海洋的形成，但时间尺度为数百万年。在埃塞俄比亚北部偏远的阿法尔凹陷，地球最外层的壳体，一个相对坚硬，约150公里厚的构造板块，已经被拉伸和加热到断裂点。从地幔涌出的岩石部分融化，上升，然后冷却，形成一个新的海洋板块。如此之多，以至于几乎形成了一个新的海洋。在这里，我们有前所未有的机会见证板块破裂和熔岩(岩浆)上涌的过程。通常，这一过程发生在浅海，或沿着已建立的海底深部扩张中心；然而，在阿法尔，我们实际上可以在发生这种情况时横穿该区域。卫星对地球的观测表明，构造板块的移动速度平均非常慢：通常是每年几厘米，或者大约是指甲生长的速度。然而，偶尔也会发生突然的大规模流动，往往会造成毁灭性的后果。2005年9月，阿法尔凹陷60公里处的一系列裂缝裂开，板块对拉开它的力量做出了灾难性的反应。在大约一周的时间里，裂缝撕裂了8米，并下降了1米。据当地人说，9月26日发生了一系列地震，预示着一块熔岩浮出了地表，火山灰使当地的空气变暗了3天。与此同时，追踪该地区的卫星显示，附近火山上方的地表下沉了3米之多，因为岩浆沿着地表下的裂缝注入。破裂的速度和巨大的长度并不出人意料，但以前从未被直接测量过。阿法尔凹陷又热又干，几乎没有植被遮盖暴露在其顶部表面的火山岩和沉积岩；这也意味着我们可以使用卫星对它们进行成像，并测量地球表面随着断层移动和加压熔岩漂浮上升并沿着裂谷内的裂缝长度向上移动的方式。自第一次大地震以来的九个月里，地表继续发生更戏剧性的变化，地震继续搅动地球和当地居民。我们正在提出一套重要的实验，将把地球变形、地球磁场和电场以及岩浆运动和喷发的专家聚集到这个独特的自然实验室。在未来五年里，这个由英国、埃塞俄比亚、美国和新西兰科学家组成的团队将合作回答板块构造的基本问题：盘子的不同层是如何伸展开的？熔岩在哪里形成并上升形成新的洋壳？熔岩是如何向上移动到地表的？卫星将从上方为地球成像，传感器将记录来自远震和近震的声波和自然磁信号，以成像板块组成的岩层的厚度。我们还将收集和分析同一地区年轻火山的岩石成分。从空间和时间的组成变化推断出的地球历史将给我们提供线索，告诉我们类似的事件在过去发生的时间和频率/以及未来可能再次发生的情况。

The African continent is slowly splitting apart along the East African rift valley, a 3000 km-long series of deep basins and flanking mountain ranges. This process may eventually lead to the formation of a new ocean, but on a time scale of millions of years. In the remote Afar depression in northern Ethiopia, Earth's outermost shell, a relatively rigid, ~150 km-thick tectonic plate, has been stretched and heated to the point of rupture. Upwelling rocks from Earth's mantle partially melt, rise, and then cool to form a new oceanic plate. so much that a new ocean has nearly been formed. Here, we have the unprecedented opportunity to witness the process of plate rupture and upwelling of molten rock (magma). Normally, this process occurs within shallow seas, or along the established seafloor spreading centres deep under the sea; in Afar, though, we can actually walk across the region as it happens. Satellite observations of the earth show that tectonic plates move apart, on average, very slowly: usually at a few centimentres per year, or about the rate of fingernail growth. Very occasionally, however, sudden large movements occur, often with devastating consequences. In September 2005, a series of fissures opened along a 60 km section of the Afar depression, as the plate responded catastrophically to forces pulling it apart. Over about a week, the rift pulled apart by 8 metres, and dropped down by up to 1 metre. As told by local people, a series of earthquakes signalled the rise of a block of molten rock to the surface on September 26, and ash darkened the air locally for 3 days. At the same time, satellites tracking the region showed that the surface above nearby volcanoes subsided by as much as 3 metres, as magma was injected along the fissure below the surface. The rapidity and immense length of rupture are not unexpected, but have never before been measured directly. The Afar depression is so hot and dry that there is almost no vegetation to obscure the volcanic and sedimentary rocks exposed on its top surface; this also means that we can use satellites image the them and to measure the way that the Earth's surface changes as faults move, and as pressurised molten rock buoyantly rises and moves up and along the length of fissures within the rift valley. In the nine months since the first major earthquakes, more dramatic surface changes have continued to take place, and earthquakes continue to stir the earth, and local inhabitants. We are proposing a major set of experiments that will bring together experts on Earth deformation, Earth's magnetic and electrical fields, and on magma movement and eruption to this unique natural laboratory. Over the next five years, this team of UK, Ethiopian, US, and New Zealand scientists will collaborate to answers to fundamental questions of plate tectonics: . How do the different layers of the plate stretch apart? . Where does molten rock form and rise to form new oceanic crust? . How does the molten rock move up to the surface? Satellites will image the earth from above, and sensors will record sound waves from distant and near earthquakes and natural magnetic signals to image the thickness of the rock layers the plate comprises. We will also collect and analyse the composition of rocks from young volcanoes in the same region. The Earth history deduced from compositional variations in space and time will give us clues as to when and how often similar sorts of events happened in the past / and may happen again in the future.