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The behaviour of the lithosphere on seismic to geologic time-scales and its implications for landscape evolution and mantle dynamics

岩石圈在地震到地质时间尺度上的行为及其对地貌演化和地幔动力学的影响

基本信息

批准号：
NE/I026839/1
负责人：
Anthony Brian Watts
金额：
$ 39.72万
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FI026839%2F1
关键词：
behaviour lithosphere seismic geologic time

项目摘要

The lithosphere, which is the strong rocky outermost layer of the Earth on which we live, is made up of a number of large plates and several smaller ones which are in motion with respect to each other and the deep mantle below. According to plate tectonic theory, the plates are rigid and deformation is limited to their boundaries. But how do we know how rigid the plates are? The principal evidence has come from studies of the way the lithosphere deforms in response to loads that have been emplaced on its surface or base. Examples of such loads include earthquakes, the waxing and waning of ice sheets, the growth and decay of volcanoes and the deposition, slumping and sliding of sediment. While these loads have been applied over a range of temporal and spatial scales and so only provide a "snapshot" of lithosphere behaviour, they have provided us with a useful insight into how the plates might actually deform in response to past and, interestingly, future loads.Previous studies at submarine volcano loads suggest that as the lithosphere cools and subsides with age its strength increases. Volcanoes that form on young seafloor (i.e. on near a mid-ocean ridge crest) are emplaced on weak lithosphere while volcanoes emplaced on old seafloor (i.e. on a ridge flank) are emplaced on strong lithosphere. The same studies reveal, however, that when a volcano loads a particular thermal age of seafloor the underlying lithosphere relaxes such that it weakens with load age. There therefore appears to be a competition between thermal cooling which strengthens the lithosphere and a load-induced stress relaxation that weakens it. The strength of the lithosphere is a fundamental parameter that controls the "architecture" of sedimentary basins and the structural styles that develop in extensional, compressional and strike-slip faulting settings. We propose here therefore to compile all the available field and laboratory observations that relate to lithospheric strength and then construct a computer model that predicts how the lithosphere responds to loads on seismic (i.e. short) through geologic (i.e. long) time-scales. Our model, which will incorporate the effects of both strengthening due to cooling and weakening due to stress relaxation, has major implications for geological processes, especially landscape evolution and mantle dynamics. In landscape evolution, for example, we aim to use the model to predict the deformation that occurs in the near-field of ice loads and unloads where previous work has shown that the strength of the lithosphere plays a major role in controlling bedrock geometry, which in turn influences estimates of ice and melt-water volume. We will also use the new model to evaluate the effects of sediment and water loading and unloading on the development of topography during glacial/inter-glacial cycles when our preliminary models show that the strength of the lithosphere can influence the course of rivers through changes in base-level and shelf grade. The proposed work, by focussing on the lithosphere and how it interacts with the cryosphere, hydrosphere and atmosphere above and the asthenosphere below, is of societal as well as scientific interest. The deformation of the lithosphere in the region of large loads, for example, is an important source of stress which may control the location of faults and earthquakes, as appears to be the case beneath Hawaii Island. Moreover, the vertical motions of the crust and mantle that occur during and following loading and unloading of the lithosphere by ice, volcanoes and sediment are all potential contributors to local sea-level change that needs to be taken into account when assessing global sea-level and its impact on past and future environmental change.

岩石圈是我们居住的地球最外层坚固的岩石层，由许多大板块和几个较小的板块组成，这些板块相互之间以及下面的地幔深处都在运动。根据板块构造理论，板块是刚性的，变形仅限于其边界。但我们怎么知道盘子的硬度呢？主要的证据来自于对岩石圈在其表面或基底上受到的载荷作用下变形方式的研究。这种负荷的例子包括地震、冰盖的消长、火山的生长和衰变以及沉积物的沉积、塌陷和滑动。虽然这些负荷已被施加在一系列的时间和空间尺度，因此只提供了一个“快照”的岩石圈的行为，他们为我们提供了一个有用的洞察板块可能实际上如何变形，以响应过去，有趣的是，未来load.Previous研究海底火山负荷表明，随着岩石圈冷却和沉降的年龄，其强度增加。形成于年轻海底（即洋中脊顶附近）的火山位于弱岩石圈上，而位于老海底（即脊侧面）的火山则位于强岩石圈上。然而，同样的研究表明，当一个火山加载一个特定的热年龄的海底，下面的岩石圈松弛，使其与负载年龄减弱。因此，似乎有一个热冷却，加强岩石圈和负载引起的应力松弛，削弱它之间的竞争。岩石圈的强度是一个基本参数，控制沉积盆地的“架构”和结构风格，在伸展，挤压和走滑断层设置发展。因此，我们建议在这里编译所有可用的现场和实验室的观察，涉及到岩石圈的强度，然后构建一个计算机模型，预测岩石圈如何响应地震（即短）通过地质（即长）的时间尺度上的负载。我们的模型，这将结合由于冷却和应力松弛的削弱，由于加强的效果，地质过程，特别是景观演化和地幔动力学具有重大意义。例如，在景观演变中，我们的目标是使用该模型来预测发生在冰载荷和卸载的近场中的变形，其中以前的工作已经表明，岩石圈的强度在控制基岩几何形状方面起着重要作用，这反过来又影响了冰和融水体积的估计。我们还将使用新的模型来评估沉积物和水的加载和卸载的影响，在冰川/间冰期周期的地形发展时，我们的初步模型表明，岩石圈的强度可以影响河流的过程中通过变化基准面和货架等级。拟议的工作重点是岩石圈及其如何与冰冻圈、水圈和大气层以及下面的软流圈相互作用，具有社会和科学意义。例如，大载荷区域岩石圈的变形是一个重要的应力源，它可能控制断层和地震的位置，就像夏威夷岛下面的情况一样。此外，在冰、火山和沉积物对岩石圈进行加载和卸载期间及之后发生的地壳和地幔的垂直运动，都是造成当地海平面变化的潜在因素，在评估全球海平面及其对过去和未来环境变化的影响时，需要考虑到这一点。