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缓慢分裂，裂谷是一个3000公里长的一系列深盆地和两侧的山脉。这一过程可能最终导致新海洋的形成，但需要数百万年的时间。在埃塞俄比亚北部遥远的阿法尔洼地，地球的最外层，通常是一个相对坚硬的150公里厚的板块，已经被拉伸、变薄和加热到破裂的程度，以至于一个新的海洋即将形成。在地表之下，来自地幔的上涌岩石部分融化、上升和冷却。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中，或沿着海洋深处已形成的海底扩散中心；而在阿法尔，我们可以步行穿越整个地区。对地球的卫星观测显示，构造板块分开的速度平均非常缓慢：通常每年几厘米，或者大约是指甲生长的速度。然而，在非常偶然的情况下，会发生突然的大运动，通常会带来毁灭性的后果。2005年9月，阿法尔洼地60公里长的一段出现了一系列裂缝，这是板块在拉力作用下产生的灾难性反应。在大约一周的时间里，裂缝裂开了8米，并下降了1米。据当地居民说，9月26日，一系列地震预示着熔岩上升到地表，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，随着岩浆沿着地表以下的裂缝注入，附近火山上方的表面下沉了多达3米。破裂的速度之快和长度之长并不出人意料，但以前从未被直接测量过。阿法尔洼地是如此炎热和干燥，几乎没有植被掩盖裸露在其顶部表面的岩石；这也意味着我们可以用卫星来拍摄它们，并测量断层移动时地球表面的变化方式，以及压力熔融岩石沿着裂谷内裂缝的长度向上移动的方式。在第一次大地震发生后的九个月里，更剧烈的地表变化继续发生，地震继续搅动着地球。我们正在提议一套主要的实验，将把地球变形、岩浆来源、运动和喷发方面的专家聚集到这个独特的自然实验室。在接下来的五年里，一个由英国、埃塞俄比亚和美国科学家组成的团队将合作寻找板块构造基本问题的答案：。板块的不同层是如何分开的？． 熔岩在哪里形成并上升形成新的海洋地壳？． 熔岩是如何上升到地表的？卫星将从高空拍摄地球的图像，传感器将记录来自远近地震和自然磁信号的声波，从而绘制出板块所组成的岩层的厚度，并在喷发前发现岩浆的位置。我们还将收集和分析来自同一地区年轻火山的岩石组成。从空间和时间的成分变化中推断出的地球历史将为我们提供线索，让我们知道类似的事件在过去发生的时间和频率，以及将来可能再次发生的频率。

Summary 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, usually a relatively rigid, 150 km-thick plate, has been stretched, thinned and heated to the point of rupture, to the extent that a new ocean is about to form. Below the surface, upwelling rocks from Earth's mantle below are partially melting, rising, and cooling. 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 oceans; 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 centimetres 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 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 almost no vegetation obscures the rocks exposed on its top surface; this also means that we can use satellites to image them and to measure the way that the Earth's surface changes as faults move, and as pressurised molten rock 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. We are proposing a major set of experiments that will bring together experts on Earth deformation, and on magma sources, movement and eruption to this unique natural laboratory. Over the next five years, a team of UK, Ethiopian and US scientists will collaborate to find 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, and discover where the magma is located prior to eruption. 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.