Feedbacks between mineral reactions and mantle convection

矿物反应与地幔对流之间的反馈

• 批准号: NE/V018221/1
• 负责人: J Davies
• 金额: $ 4.54万
• 依托单位: CARDIFF UNIVERSITY
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV018221%2F1
• 关键词: Feedbacks; between; mineral; reactions; mantle

The evolution of the solid Earth and many surface features are controlled by movements deep within. We aim to transform our understanding of those movements through a new understanding of mineral behaviour. Rocks in the mantle, the outer half of the Earth, can flow despite being solid, in the same way that a glacier flows. This flow is driven by contrasts in density, for example dense material sinks. One control on density is mineralogy, so we need to understand the controls on mineral changes. Pressure is key, for example, graphite (a form of carbon) transforms into diamond (a denser form of carbon) with increasing pressure. Pressure increases with depth in the Earth, in the same way as it does in the deep oceans. However, in a flowing system, pressure may not relate simply to depth. Another control on mineralogy is stress (different force per unit area in different directions), which prevails in the mantle as it deforms.These ideas are illustrated by a simple analogy with clouds. On a calm day, the bases of clouds often appear undisturbed at a particular level, above which water is condensing. On a day of livelier weather, the cloud bases can be disturbed, as the wind wafts them up and down, and it takes time for water to evaporate or condense in response. Thus, looking at the bases of the clouds from a distance tells us something about the on-going dynamics in the atmosphere. Similarly, in the mantle, we have mineral changes at specific levels which we can "see" using seismic waves. In places the levels vary sideways, sometimes explained in terms of varying chemistry. We propose that this may in some places be like the effects on the cloud bases, in which case the observed levels are an imprint of the on-going dynamics. We aim to understand the pressures and stresses in a flowing mantle and predict their effects on mineralogy. The changing mineralogy will affect density, which in turn affects the flow patterns. Changing mineralogy affects flow, and flow affects mineralogy - this is called feedback. We will undertake four tasks to understand this feedback.1. New experiments on minerals at mantle conditions (250,000 atmospheres pressure, temperatures up to 1800 C) measuring evolving mineral properties. To understand how the minerals change, we will examine the experimental products to discover the details of structure and chemistry within individual grains. These details will enable us to understand how the atoms have moved around, information needed for the second task. 2. Creation of mathematical models to explain the results of the experiments. The mathematics is required to use what happens in days in the experiments to predict what happens in the mantle over millions of years. 3. Taking those predictions and including them in a numerical model for flow in the whole mantle. This model will be used to predict what happens when large dense objects (tectonic plates) sink into the mantle (e.g under Japan and South America) and find out what effect the mineral changes have. It will also be used to model what happens when hot less dense material (e.g. under Hawaii and Iceland) rises towards the surface.4. Predictions of mantle mineralogy will be tested using seismic waves from earthquake, which travel at varying speeds as they pass through rocks with varying densities. Seismic waves reflect and refract due to the sharp mineral changes in the Earth. Calculations will allow us to test how seismic waves can map the features predicted in step 3. We will also collect a large data set of observed earthquake waves from across the planet to image the mineral changes occurring deep within and interpret them in terms of on-going flow patterns. In summary we will produce new mantle models that we will test using seismic wave observations and use them to produce new insights into how mineral changes and mantle flow (which controls how the Earth evolves) feedback on each other.

地球和许多表面特征的演变受到内部的运动控制。我们旨在通过对矿物行为的新理解来改变对这些运动的理解。地幔中的岩石是地球的外半，尽管固体也可以流动，就像冰川流动一样。该流程是由密度的对比度驱动的，例如密集的材料下沉。对密度的控制是矿物学，因此我们需要了解矿物质变化的控制。压力是关键，例如，随着压力的增加，石墨（一种形式的碳）转化为钻石（一种较少的碳形式）。压力随着地球的深度而增加，就像在深海中一样。但是，在流动系统中，压力可能与深度不仅关联。对矿物学的另一个控制是压力（不同方向的每单位区域的不同力），它在地幔中占上风。在一个平静的一天，云的基础通常在特定层面上不受干扰，在该水平上面凝结了水。在活泼的天气中，当风能上下飘动时，云底座可能会受到干扰，并且水需要时间蒸发或凝结。因此，从远处看云的基础，告诉我们有关大气中持续发展的动态的一些信息。同样，在地幔中，我们在特定水平上有矿物质变化，我们可以使用地震波“看到”。在某些地方，侧面有所不同，有时用变化的化学来解释。我们建议，在某些地方可能会像对云基础的影响一样，在这种情况下，观察到的水平是正在进行的动态的烙印。我们的目标是了解持流的地幔中的压力和压力，并预测它们对矿物学的影响。变化的矿物学将影响密度，进而影响流动模式。变化的矿物学会影响流动，流动影响矿物学 - 这称为反馈。我们将承担四个任务以了解此反馈1。在地幔条件下进行矿物质的新实验（250,000个大气压力，高达1800 c的温度）测量不断发展的矿物质。为了了解矿物如何变化，我们将检查实验产品，以发现单个晶粒内的结构和化学细节。这些细节将使我们能够了解原子如何移动，第二任任务所需的信息。 2。创建数学模型来解释实验的结果。需要数学来使用实验中几天内发生的事情来预测数百万年内地幔中发生的情况。 3.将这些预测并包括在整个地幔中流量的数值模型中。该模型将用于预测当大型密集物体（构造板）沉入地幔（例如在日本和南美下）并找出矿物变化的影响时会发生什么。它也将用于建模当热较少的材料（例如夏威夷和冰岛下）朝向表面时会发生什么。4。地幔矿物学的预测将使用地震中的地震波进行测试，地震的地震波在穿过岩石时以不同密度的岩石的速度行驶。地震波反射和折射，这是由于地球上的急剧变化。计算将使我们能够测试地震波如何绘制步骤3中预测的特征。我们还将收集一大批观察到的地震波的数据集，以图像在内部深处发生的矿物变化，并根据持续的流动模式来解释它们。总而言之，我们将生成新的地幔模型，我们将使用地震波观测来测试，并使用它们来对矿物的变化和地幔流（控制地球如何发展）的反馈产生新的见解。