Continental extension leading to breakup: determining the 3D structure of the west Galicia rifted margin

大陆伸展导致分裂：确定西加利西亚裂谷边缘的 3D 结构

基本信息

批准号：
NE/E016502/1
负责人：
Timothy Reston
金额：
$ 40.36万
依托单位：
University of Southampton
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FE016502%2F1
关键词：
Continental extension leading breakup determining

项目摘要

It has been widely accepted since the 1960s that the Earth's continental landmasses are not fixed, and that over periods of millions of years continents can separate and coalesce, for that for example the landmasses that make up the United Kingdom were once joined to Greenland and North America. The breakup of continents is commonly preceded by a long period of stretching, during which the continental crust is thinned and sediments accumulate in thick piles which may become future sources of oil and gas. During the last decade, researchers have discovered that, at least in some places, the nature of this stretching changes dramatically when the crust becomes thinner than 8-10 km. The top few kilometers of the crust are brittle, and initially stretch by movement along steeply dipping faults, but once this thickness threshold is crossed, the extension is instead accommodated on faults that are close to horizontal. This type of behaviour is also seen in other geological settings, such in the western United States, where the crust may be unusually weak, and close to volcanic mid-ocean ridges. The best-studied example of such behaviour is off the west coast of the Iberian peninsula. In such locations, faults lying deep beneath the seafloor can be seen in images derived from sound waves / the 'seismic reflection' technique. The application of this technique has revealed beneath the broken, fractured brittle crust the presence of a sub-horizontal fault covering an area of at least 1000 square kilometers (the size of the West Midlands) that was active when Iberia broke away from Newfoundland over 100 million years ago. Such faults can have very complicated shapes and interactions with the broken crustal blocks above, and because the existing images are just along a series of lines several kilometers apart, it is very difficult to work out how the fault moved. We will solve this problem by collecting a series of very closely spaced seismic reflection images that can be combined on a computer into a three-dimensional picture. This approach has been widely used by the oil industry in areas thought to contain economically viable oil and gas deposits, but never before to study the first order process of continental breakup itself. To make the most of the image, we will also collect another type of seismic data that allows us to work out how the speed of sound varies beneath the seafloor and hence what type of rocks may be present. As well us providing a detailed picture of how this particular pair of continents broke apart, the experiment will provide the most detailed and complete image ever of a large fault surface, and reveal how this fault and other more steeply-dipping faults above it have moved over millions of years. These observations will help us to understand more generally how the crust stretches and how large faults work.

自1960年代以来，它已被广泛接受，即地球的大陆大陆不是固定的，并且在数百万年的大洲可以分开并结出结合，例如，构成英国的陆地曾经曾经加入格陵兰岛和北美。大陆的破裂通常是在长时间拉伸之前，在此之前，大陆地壳被稀薄，沉积物积聚在厚厚的堆中，这可能会成为未来的石油和天然气来源。在过去的十年中，研究人员发现，至少在某些地方，当外壳变得比8-10公里稀薄时，这种拉伸的性质发生了巨大变化。地壳的前几公里是脆弱的，最初是通过沿陡峭的浸入断层运动而伸展的，但是一旦越过这个厚度阈值，该延伸就可以容纳在接近水平的断层上。在其他地质环境中也可以看到这种行为，例如，在美国西部，地壳可能异常疲软，并且接近火山中部山脊。这种行为的最佳研究例子是在伊比利亚半岛的西海岸附近。在这样的位置，可以在源自声波 /“地震反射”技术的图像中看到位于海底深处的断层。该技术的应用揭示了碎裂的脆皮破裂的下方，当时伊比利亚从纽芬兰（Newfoundland）脱离了1亿年前，覆盖了至少1000平方公里（西米德兰兹（West Midlands）的大小）的区域。这样的故障可能具有非常复杂的形状和与上面的地壳破裂块的相互作用，并且由于现有图像仅沿着一系列线相距几公里，因此很难弄清楚故障如何移动。我们将通过收集一系列非常距离的地震反射图像来解决这个问题，这些反射图像可以在计算机上组合为三维图片。石油工业在被认为包含经济上可行的石油和天然气矿床的地区广泛使用了这种方法，但从来没有研究过大陆拆分本身的一级过程。为了充分利用图像，我们还将收集另一种类型的地震数据，使我们能够确定声音速度如何在海底下方变化，从而可能存在哪种类型的岩石。除了提供有关这对特定大陆如何破裂的详细图片，该实验还将提供有史以来最详细，最完整的图像，并揭示该故障和其他更陡峭的故障在数百万年内移动了数百万年。这些观察结果将有助于我们更广泛地了解外壳的伸展方式以及大缺陷的工作方式。