The Feedback Between Volatiles and Mantle Dynamics

挥发物与地幔动力学之间的反馈

基本信息

批准号：
NE/M000060/1
负责人：
Elisabetta Mariani
金额：
$ 46.19万
依托单位：
University of Liverpool
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FM000060%2F1
关键词：
Feedback Between Volatiles Mantle Dynamics

项目摘要

In 2011, NERC began a scoping exercise to develop a research programme based around deep Earth controls on the habitable planet. The result of this exercise was for NERC to commit substantial funding to support a programme entitled "Volatiles, Geodynamics and Solid Earth Controls on the Habitable Planet". This proposal is a direct response to that call. It is widely and generally accepted that volatiles - in particular water - strongly affect the properties that control the flow of rocks and minerals (their rheological properties). Indeed, experiments on low-pressure minerals such as quartz and olivine show that even small amounts of water can weaken a mineral - allowing it to flow faster - by as much as several orders of magnitude. This effect is known as hydrolytic weakening, and has been used to explain a wide range of fundamental Earth questions - including the origin of plate tectonics and why Earth and Venus are different. The effect of water and volatiles on the properties of mantle rocks and minerals is a central component of this NERC research programme. Indeed it forms the basis for one of the three main questions posed by the UK academic community, and supported by a number of international experts during the scoping process. The question is "What are the feedbacks between volatile fluxes and mantle convection through time?" Intuitively, one expects feedbacks between volatiles and mantle convection. For instance, one might envisage a scenario whereby the more water is subducted into the lower mantle, the more the mantle should weaken, allowing faster convection, which in turn results in even more water passing into the lower mantle, and so on. Of course this is a simplification since faster convection cools the mantle, slowing convection, and also increases the amount of volatiles removed from the mantle at mid-ocean ridges. Nevertheless, one can imagine many important feedbacks, some of which have been examined via simple models. In particular these models indicate a feedback between volatiles and convection that controls the distribution of water between the oceans and the mantle, and the amount topography created by the vertical movement of the mantle (known as dynamic topography). The scientists involved in the scoping exercise recognized this as a major scientific question, and one having potentially far reaching consequences for the Earth's surface and habitability.However, as is discussed in detail in the proposal, our understanding of how mantle rocks deform as a function of water content is remarkably limited, and in fact the effect of water on the majority of mantle minerals has never been measured. The effect of water on the flow properties of most mantle minerals is simply inferred from experiments on low-pressure minerals (olivine, pyroxenes and quartz). As argued in the proposal, one cannot simply extrapolate between different minerals and rocks because different minerals may react quite differently to water. Moreover, current research is now calling into question even the experimental results on olivine, making the issue even more pressing. We propose, therefore, a comprehensive campaign to quantify the effect of water on the rheological properties of all the major mantle minerals and rocks using a combination of new experiments and multi-physics simulation. In conjunction with 3D mantle convection models, this information will allow us to understand how the feedback between volatiles and mantle convection impacts on problems of Earth habitability, such as how ocean volumes and large-scale dynamic topography vary over time. This research thus addresses the aims and ambitions of the research programme head on, and indeed, is required for the success of the entire programme.

2011年，NERC开始进行范围的练习，以围绕宜居行星的深层控制制定研究计划。这项练习的结果是NERC投入大量资金，以支持一项名为“易居行星上的挥发物，地球动力学和固体地球控制”的计划。该建议是对该电话的直接回应。普遍认为，挥发物（尤其是水）强烈影响控制岩石和矿物质流动的特性（其流变特性）。实际上，在低压矿物质（例如石英和橄榄石）上进行的实验表明，即使是少量水也可以削弱矿物质 - 使其流动更快 - 高达几个数量级。该作用称为水解弱化，已用于解释广泛的地球问题 - 包括板块构造的起源以及地球和金星为何不同。水和挥发物对地幔岩石和矿物质性质的影响是该NERC研究计划的核心组成部分。确实，它构成了英国学术界提出的三个主要问题之一的基础，并在范围内的许多国际专家支持。问题是“随着时间的流逝，挥发性通量和地幔对流之间的反馈是什么？”直觉上，人们期望挥发物和地幔对流之间会有反馈。例如，人们可能会设想一种场景，从而使越过下地幔的水越来越多，地幔越应削弱，可以使对流更快，进而导致更多的水进入下层地幔，依此类推。当然，这是一种简化的，因为更快的对流会冷却地幔，减慢对流的速度，并增加从中山脊处的地幔中去除的挥发物量。然而，人们可以想象许多重要的反馈，其中一些已经通过简单模型进行了检查。特别地，这些模型表明挥发物与对流之间的反馈控制了海洋和地幔之间水的分布，以及由地幔的垂直运动（称为动态地形）创建的数量地形。参与范围练习的科学家认为这是一个主要的科学问题，并且对地球的表面和可居住性产生了遥远的后果。但是，正如提案中详细讨论的那样，我们对地幔岩石与水含量如何变形的理解是非常有限的，实际上对大多数梅尔特尔人的效果对水的影响是非常有限的。水对大多数地幔矿物的流量性能的影响仅是从低压矿物（橄榄石，辉石和石英）上的实验中推断出来的。正如提案中所说的那样，由于不同的矿物质可能对水的反应截然不同，因此不能简单地推断出不同的矿物质和岩石。此外，当前的研究甚至质疑有关橄榄石的实验结果，使问题更加紧迫。因此，我们提出了一项全面的运动，旨在量化水对所有主要地幔矿物质和岩石的流变特性的影响，结合使用新实验和多物理学模拟。结合3D地幔对流模型，此信息将使我们能够了解挥发物和地幔对流之间的反馈如何影响地球可居住性问题，例如海洋体积和大规模动态地形如何随着时间而变化。因此，这项研究解决了研究计划的目标和野心，实际上是整个计划成功所必需的。