Origin, structure and deformation of low-magmatic oceanic lithosphere in the vicinity of ODP Leg 209, Mid-Atlantic Ridge 14oN - 16oN.

当构造板块分离时，地球上地幔中的橄榄岩上升并融化，然后熔融冷却形成洋壳。一般来说，这个地壳有6-7公里厚，但在一些地区，它要薄得多，可能会完全消失。这种情况发生在大西洋中部海脊的第15-20断裂带附近。在这里，橄榄岩沿着山脊轴线广泛露出数十公里，分布在复杂的地形和断层地带。这提供了一个极好的机会，既可以研究地幔岩石，也可以研究在没有实质性熔融或厚壳的情况下海底扩张过程。大洋钻探计划已经在该地区钻了八个深孔，我们将通过非常详细的测绘和采集更多浅层样本来补充这项工作。我们将使用声纳拍摄海底图像，并用它来绘制断层和不同岩石类型的地图。然后，我们将选择最多60个浅岩心的地点。这些样品将在空间上定向，使我们能够确定流动方向、地幔岩石侵位时的拉伸和破裂以及随后的断层旋转等性质。化学分析将使我们能够解开这些岩石起源的细节，以及它们是如何熔化和随后演化的。

When tectonic plates separate, the peridotite rock in the Earth's upper mantle rises and melts, then the melt cools to form oceanic crust. Generally this crust is 6-7 km thick, but in some areas it is much thinner and may be missing altogether. Such a situation occurs around the Fifteen Twenty Fracture Zone on the Mid-Atlantic Ridge. Here, peridotite crops out extensively for tens of kilometres along the ridge axis, in zones marked by complex topography and faulting. This provides a superb opportunity to study both rocks from the mantle, and the processes by which seafloor spreading takes place in the absence of substantial melt or a thick crust. The ocean drilling programme has already drilled eight deep holes in the area, and we will complement that work with very detailed mapping and taking many more shallow samples. We will image the seafloor using sonar, and use this to map the faults and different rock types. We will then choose sites where we will take up to 60 shallow cores of rock. These samples will be oriented in space, allowing us to determine properties such as the directions of flow, stretching and fracturing as the mantle rocks were emplaced, and subsequent rotations by faulting. Chemical analysis will enable us to unravel details of where these rocks originated and how they melted and subsequently evolved.