Pulsing Mantle Plumes: Causes and Geological Consequences

在地壳和地核之间是地幔，2,900公里的热岩，占地球体积的80%。对流地幔将地球内部的热量带到地表，就像炎热的日子里的焦油一样蠕动。这种翻转是驱动我们动态地球的“引擎”;所有大规模的地质活动都是由地幔对流驱动的。地幔柱是地幔对流的一个重要方面，但了解甚少。它们是有浮力的地幔隆起，将地球深部地幔的热物质带到地表，在它们上升的过程中抬升地球表面，并产生大型火山区和火山岛，如冰岛和夏威夷。越来越多的证据表明，这些上升流羽流的形状和强度随着时间的推移而变化;它们脉动。这样的脉冲产生相应的表面形貌的变化，这对一系列的表面过程有重大影响。举例来说：（i）碳氢化合物的生成-沉积物供应的变化受构造抬升和随后的侵蚀的驱动，对沉积盆地的地层有很大影响，而地层最终控制了碳氢化合物的分布;和（ii）海洋环流-脉动的冰岛地幔柱在控制区域隆起方面发挥了核心作用，反过来，减缓了北大西洋深层冷水溢出进入全球海洋环流系统。该系统在地球仪中传输能量（以热量的形式）和物质（固体、溶解物质和气体）。因此，脉动地幔柱对全球气候有直接影响。虽然脉冲的观测证据越来越多，但最终原因尚不清楚。因此，我们无法解释或预测脉冲的强度和频率，或它们在地球表面的特征。如果我们要了解地球的地质历史和地幔的长期演化，那么建立脉冲羽流和它们的表面表现之间的关系是很重要的。为了解决目前理解中的这些差距，拟议的研究将使用最先进的数值地幔对流模型来研究引起地幔柱脉冲的机制，并预测表面对这些脉冲的响应。脉冲的原因将通过数值测试一系列假设来确定;例如，上升流的速率是由冷地壳材料下沉板的强迫变化控制的。每一个假设将通过比较模型预测的脉冲行为与地质观测，主要是从北大西洋。模型也将被用来预测地球表面如何对这些脉冲作出反应;例如，当上升流增加和减少时，地球表面何时、何地以及上升多少。这些预测将通过观测北大西洋对冰岛地幔柱脉动的反应来检验。除了解决地球科学中一个长期存在的问题外，这项研究的一个重要成果将是建立一个地球表面对地球内部流动反应的预测模型。换句话说，该模型将显示地球的“引擎”-地幔对流-如何驱动表面变形。这种联系对于推进研究地球动态表面后果的地球科学的许多领域至关重要。

Between Earth's crust and core lies the mantle, 2,900-km of hot rock that comprises 80% of Earth's volume. Carrying Earth's internal heat to the surface, the convecting mantle creeps like tar on a hot day. This overturning is the 'engine' that drives our dynamic Earth; all large-scale geological activity is driven by mantle convection. Mantle plumes are an important, but poorly understood, aspect of mantle convection. They are buoyant mantle upwellings that bring hot material from Earth's deep mantle to the surface, lifting Earth's surface as they rise and generating large volcanic provinces and volcanic islands, such as Iceland and Hawaii. There is increasing evidence that these upwelling plumes change in shape and strength through time; they pulse. Such pulses produce corresponding changes in surface topography, which has major implications for a range of surface processes. For example: (i) hydrocarbon generation - variations in sediment supply, which are driven by tectonic uplift and subsequent erosion, strongly influence the stratigraphy of sedimentary basins, which ultimately controls the distribution of hydrocarbons; and (ii) ocean circulation - the pulsing Icelandic mantle plume has played a central role in controlling regional uplift, which, in turn, has moderated overflow of cold North Atlantic Deep Water into the global ocean circulation system. This system transports both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. Consequently, pulsing mantle plumes have a direct influence on global climate. While the observational evidence for pulsing is increasing, the ultimate cause is unknown. Consequently, we cannot explain or predict the strength and frequency of pulses, or their signature at Earth's surface. Establishing a relationship between pulsing plumes and their surface manifestation is important if we are to understand Earth's geological history and the long-term evolution of Earth's mantle. To address these gaps in current understanding, the proposed research will use state-of-the-art numerical mantle convection models to investigate the mechanisms that cause pulsing in mantle plumes and to predict the surface response to these pulses. The cause of pulsing will be established by numerically testing a range of hypotheses; for example, that the rate of upwelling is controlled by changes in forcing from sinking slabs of cold crustal material. Each hypothesis will be validated by comparing model predictions of pulsing behavior with geological observations, predominantly from the North Atlantic Ocean. Models will also be used to predict how Earth's surface responds to these pulses; for example, when, where and by how much the surface is uplifted as the upwelling waxes and wanes. These predictions will be tested against observations of how the North Atlantic has responded to the pulsing Icelandic mantle plume. As well as solving a long-standing problem in Earth science, an important outcome of this research will be a predictive model of the response of Earth's surface to flow within Earth's interior. In other words, the model will show how Earth's 'engine' - mantle convection - drives surface deformation. Such a connection is vital for advancing the many fields of Earth sciences that examine the consequences of Earth's dynamic surface.