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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20世纪60年代以来，人们普遍认为地球的大陆并不是固定的，在数百万年的时间里，大陆可以分离和合并，例如组成英国的大陆曾经与格陵兰岛和北美相连。大陆分裂之前通常会有一段长时间的拉伸，在此期间，大陆地壳变薄，沉积物堆积成厚堆，可能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，当地壳变得薄于8-10公里时，这种拉伸的性质发生了巨大的变化。地壳的顶部几公里是脆弱的，最初沿着沿着陡峭倾斜的断层运动而伸展，但是一旦超过这个厚度阈值，伸展就被接近水平的断层所适应。在其他地质环境中也可以看到这种行为，例如在美国西部，那里的地壳可能异常脆弱，并靠近火山洋中脊。对这种行为研究得最多的例子是伊比利亚半岛西海岸。在这些位置，可以在声波/“地震反射”技术获得的图像中看到深埋在海底下的断层。这项技术的应用揭示了在破碎的脆性地壳下面存在一个近水平断层，覆盖面积至少为1000平方公里（相当于西米德兰兹郡的大小），该断层在1亿多年前伊比利亚从纽芬兰分离时就处于活动状态。这样的断层可能具有非常复杂的形状，并与上面破碎的地壳块体相互作用，因为现有的图像只是沿着沿着一系列相隔几公里的线，所以很难弄清楚断层是如何移动的。我们将通过收集一系列间隔很近的地震反射图像来解决这个问题，这些图像可以在计算机上组合成三维图像。这种方法已被石油工业广泛用于被认为含有经济上可行的石油和天然气矿床的地区，但以前从未研究过大陆分裂本身的一级过程。为了充分利用图像，我们还将收集另一种类型的地震数据，使我们能够计算出海底下的声速如何变化，从而确定可能存在何种类型的岩石。除了我们提供了这对大陆如何分裂的详细图片外，实验还将提供有史以来最详细和完整的大型断层表面图像，并揭示该断层及其上方其他更陡峭的断层如何移动数百万年。这些观测将帮助我们更全面地了解地壳是如何伸展的，以及大断层是如何活动的。