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.

地幔是地球最大的组成部分，占地球体积的 84%。尽管地幔是固体，但在地质时期，它会像流体一样剧烈地搅动，这一过程被称为地幔对流，这是由地球内部放射性衰变产生的热量和来自上方的冷却所驱动的。地幔对流使地球整个表面变形为由隆起和凹陷组成的连锁图案，被称为“动态地形”，其直径为数千公里，高度为数公里。动态地形影响洋流模式、陆地表面侵蚀和侵蚀沉积物的积累，已知这些影响控制着宝贵的天然矿产资源的分布。火山活动通常也与对流循环中炽热、上升的元素（称为地幔柱）有关。最活跃的地幔柱会产生大型火成岩省（LIP）——不定期的大量熔岩喷发，同时向大气中释放大量温室气体。 LIP 与地球历史上一些对全球气候、生态系统和碳循环最显着的扰动同时发生，包括大规模灭绝、海洋缺氧事件和新生代最大的自然全球变暖事件。对流在地质时期（数千万年或更长时间）影响了地球表面和气候过程，这些时间框架太慢，无法解释环境变化的快速发生和持续时间短通常与 LIP 一致。但现在越来越多的证据表明，地幔对流、动态地形和火成岩喷发的模式可以在不到一百万年的时间内演化。该理论的关键是一个被称为“热羽流脉冲”的过程，其中较热和较冷的地幔团随着地幔羽流内的对流循环而被携带。最大的地幔柱（例如冰岛地幔柱）内最热的脉冲可以以超过 200 毫米/年的速度上升，这比构造板块的运动还要快，并可能导致当地海平面变化超过 1毫米/年，类似于现代平均全球海平面变化。以这样的速度，过去冰岛地幔柱的脉动可能足够快地激活北大西洋LIP产生温室气体，足以解释古新世-始新世热最大值极端全球气候变化事件，这是人为气候变化的最佳自然模拟。由于缺乏关键数据，地幔柱脉冲假说并未被冰岛或地球其他主要地幔柱普遍接受。对冰岛附近被称为“V 形海脊”（VSR）的海底特征进行高质量测量将弥补这一差距，这些海底特征构成了世界上建议的热脉冲的最佳记录。我们与 VSR 替代模型的主要倡导者合作，设计了一项实验，通过测量构成 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，并且很快将通过国际钻探项目得到加强。现在，IMPULSE 将首次测量几个 VSR 下方整个地壳的厚度和地震速度（因此整体成分）的变化。我们的试点工作表明，IMPULSE 将为百万年时间范围内地幔温度的波动提供确凿的证据为地幔柱脉冲假说提供第一个明确的证据。此外，通过首次正式修正洋中脊构造过程对 VSR 地壳厚度的复杂影响，我们的新 VSR 记录将确定地幔温度波动的最短时间段。这些结果对于检验地幔对流如何影响地球表面和气候过程的假设至关重要。