IMPULSE: Taking the Pulse of the Icelandic Mantle Plume

冲动：把握冰岛地幔柱的脉搏

• 批准号: NE/V012878/1
• 负责人: Stephen Jones
• 金额: $ 88.62万
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV012878%2F1
• 关键词: IMPULSE; Taking; Pulse; Icelandic; Mantle

The mantle is the largest component of the Earth, comprising 84% of our planet's volume. Although the mantle is solid, over geological time it churns vigorously like a fluid in a process known as mantle convection, driven by heating from radioactive decay in Earth's interior and cooling from above. Mantle convection deforms the Earth's entire surface into an interlocking pattern of swells and depressions known as "dynamic topography", with diameters of several thousand km and heights of several km. Dynamic topography influences oceanic current patterns, land surface erosion and accumulation of the eroded sediment, and these effects are known to control the distribution of valuable natural mineral resources. Volcanic activity also usually occurs in association with the hot, rising elements of the convective circulation, known as mantle plumes. The most vigorous mantle plumes give rise to Large Igneous Provinces (LIPs) - episodic huge outpourings of lava accompanied by voluminous release of greenhouse gases to the atmosphere. LIPs coincide in time with some of the most remarkable perturbations to global climate, ecosystems and the carbon cycle in Earth's history, including mass extinctions, Ocean Anoxic Events, and the largest natural global warming event of Cenozoic time.Whilst it is widely accepted that mantle convection has influenced Earth's surface and climate processes over geological time periods (tens of millions of years or more), these time frames are too slow to explain the rapid onset and short duration of the environmental changes that usually coincide with LIPs. But growing evidence now suggests that patterns of mantle convection, dynamic topography and igneous outpouring can evolve in less than a million years. Key to this theory is a process known as "Thermal Plume Pulsing", in which hotter and cooler blobs of mantle are carried along with the convective circulation within a mantle plume. The hottest pulses within the biggest mantle plumes, such as the Icelandic Mantle Plume, can rise at speeds in excess of 200 mm/yr, which is faster than the motion of tectonic plates, and can cause changes in local sea-level of over 1 mm/yr, similar to modern mean global sea-level change. At such speeds, past pulsing of the Icelandic Mantle Plume could have activated greenhouse gas generation from the North Atlantic LIP rapidly enough to explain the Paleocene-Eocene Thermal Maximum extreme global climate change event, the best natural analogue to anthropogenic climate change.However, the Plume Pulsing hypothesis is not universally accepted for Iceland or Earth's other major mantle plumes as key data is lacking. High-quality measurements of seafloor features near Iceland known as the "V-Shaped Ridges" (VSRs) that comprise the world's best record of the suggested hot pulses will address this gap. Working with the lead advocates of the alternative models for VSRs, we have devised an experiment to determine the origin of the VSRs by measuring both the thickness and the chemical composition of the crust that builds the VSRs. A high-quality geochemical survey of the basaltic seafloor was made recently, and it will soon be augmented by an international drilling project. Now, IMPULSE will measure the variation in thickness and seismic velocity (hence bulk composition) of the entire crust beneath several VSRs for the first time.Our pilot work indicates that IMPULSE will provide firm evidence for fluctuations in mantle temperature on a million-year timeframe to give the first definitive proof of the Mantle Plume Pulsing hypothesis. Furthermore, by formally correcting for the complicating effect of mid-ocean ridge tectonic processes on VSR crustal thickness for the first time, our new VSR record will determine the shortest time period for fluctuations in mantle temperature. These results are crucial to test hypotheses for how mantle convection has influenced Earth's surface and climate proceses.

地幔是地球上最大的组成部分，占我们星球体积的84％。尽管地幔是固体的，但在地质时期，它在一个称为地幔对流的过程中像液体一样剧烈地搅动，这是由于地球内部放射性衰减的加热和从上方冷却的。地幔对流将地球的整个表面变形为膨胀和凹陷的互锁模式，称为“动态形态”，直径为几千公里，高度为几公里。动态地形会影响海洋电流模式，陆地表面侵蚀和侵蚀沉积物的积累，并且已知这些作用可以控制有价值的自然矿物资源的分布。火山活性通常也与对流循环的热元素（称为地幔羽流）相关。最有力的地幔羽流产生了大火成岩省（Lips） - 熔岩的巨大倾盆大雨，伴随着大量的温室气体释放到大气中。 LIPs coincide in time with some of the most remarkable perturbations to global climate, ecosystems and the carbon cycle in Earth's history, including mass extinctions, Ocean Anoxic Events, and the largest natural global warming event of Cenozoic time.Whilst it is widely accepted that mantle convection has influenced Earth's surface and climate processes over geological time periods (tens of millions of years or more), these time frames are too slow to解释通常与嘴唇一致的环境变化的快速发作和持续时间。但是越来越多的证据表明，地幔对流，动态地形和火成岩的浇灌模式可以在不到一百万年的时间内发展。该理论的关键是一种称为“热羽脉冲”的过程，其中将地幔的热斑块与地幔羽流中的对流循环一起携带。最大的地幔羽流中最热的脉冲（例如冰岛地幔羽流）可以以超过200 mm/yr的速度上升，该速度比构造板的运动快于构造板的运动快，并且可能会导致当地海平面的1 mm/yr超过1 mm/yr的变化，类似于现代平均全球海平面变化。以这样的速度，冰岛地幔羽流的过去可能会激活北大西洋唇部的温室气体产生，足以解释古新世 - 新世热的最大最大极端全球气候变化事件，是人为气候变化的最佳天然类似物，plume脉动假设对冰脉冲的数据不普遍地接受了冰岛或地球的主要占主导地位。冰岛附近的海底特征的高质量测量值为“ V形山脊”（VSR）（VSR），构成世界上建议的热脉冲的最佳记录将解决这一差距。与VSR替代模型的铅倡导者合作，我们设计了一个实验，通过测量构建VSR的地壳的厚度和化学成分来确定VSR的起源。最近对玄武岩海底进行了高质量的地球化学调查，并将很快通过一个国际钻探项目来增加。 Now, IMPULSE will measure the variation in thickness and seismic velocity (hence bulk composition) of the entire crust beneath several VSRs for the first time.Our pilot work indicates that IMPULSE will provide firm evidence for fluctuations in mantle temperature on a million-year timeframe to give the first definitive proof of the Mantle Plume Pulsing hypothesis.此外，通过正式纠正第一次近代脊构造过程对VSR地壳厚度的复杂作用，我们的新VSR记录将确定地幔温度波动的最短时间。这些结果对于检验披风对流如何影响地球表面和气候过程的假设至关重要。