NSFGEO-NERC: Imaging the magma storage region and hydrothermal system of an active arc volcano

NSFGEO-NERC：对活弧火山的岩浆储存区域和热液系统进行成像

• 批准号: NE/X000656/1
• 负责人: Timothy Minshull
• 金额: $ 59.23万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2025
• 资助国家: 英国
• 起止时间: 2025 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX000656%2F1
• 关键词: NSFGEO; NERC; Imaging; magma; storage

Our project will use a powerful and only recently available geophysical technique to probe the interior of the hydrothermal system of an active volcano and thus gain unique new insights into how such systems work. Our target is Brothers volcano in the Pacific "Ring of Fire" about 400 km north of New Zealand. This volcano hosts one of the most active submarine hydrothermal systems in the world. It has been a focus for international study over the past two decades, culminating in scientific drilling in 2018 to recover samples and make measurements up to depths of nearly 450 m below the seafloor. Consequently it arguably the best-studied volcano of its type in the world. Hydrothermal fluids circulate in almost all volcanic systems, and this circulation is the main mechanism of chemical and heat exchange between the solid Earth and the oceans. Water sinking into the crust is heated by hot or molten rocks a few kilometres below the surface, then returns to the surface. Chemicals are exchanged with the rocks and can become concentrated in the rising fluids. Molten rock itself is an additional source of water and also gases. These fluids can vent vigorously into the ocean. As they cool and mix with seawater, the elements concentrated within them precipitate, sometimes forming large deposits containing metals such as copper and gold. Studies of the fluids, their deposits on the seabed and the surrounding altered rock have shown that: venting may either be focused or diffuse; vent fluids can have a variety of compositions, temperatures and origins; and the nature of the fluids can change as the volcano evolves. However, little is known about what lies beyond the few hundred metres depth range that can be accessed by drilling. Thus the shape of flow paths at depth and their relationship to the underlying hot or molten rock remain poorly understood. Our experiment involves using a powerful transmitter that sends electromagnetic waves into the volcano and measuring the resulting electromagnetic fluctuations using receivers on the seafloor and others towed behind the transmitter. Our measurements will be sensitive to the electrical resistivity beneath the seabed down to depths of several kilometres. Solid volcanic rocks have high resistivities, but rocks become much more conductive when they start to melt, resulting in a large contrast. Hot hydrothermal fluids are even more conductive, particularly when they are salty. Metallic mineral deposits at or close to the seabed can be more conductive again. Thus our proposed controlled source electromagnetic (CSEM) techniques can be used to image all of these features. Three-dimensional CSEM imaging is now feasible, and we will generate such images for the first time at a submarine volcano, thus achieving unprecedented resolution.We will use our resistivity image to estimate the size, shape, temperature and melt content of the heat source beneath the hydrothermal system; the temperature and salinity of the hydrothermal fluids and the shape of the pathways that they take within the crust; and the size and shape of the resulting mineral deposits. We will combine these images with results from international collaborators, including major new experiments involving sending sound waves through the volcano and further drilling and computer modelling of its evolution over time. Our results will show how the shape and internal structure of the heat source below and the faulting of the crust above that heat source drive patterns of hydrothermal circulation and thus the chemical alteration of the crust. This understanding can then be applied to other volcanoes where the subsurface structure is less well known. We will also determine the relative contributions of circulating seawater and fluids released from the heat source to the formation of mineral deposits near the seafloor, and work with partners in the mining industry to assess implications for exploration for such deposits now on land.

我们的项目将使用一种强大且最近才出现的地球物理技术来探测活火山热液系统的内部，从而获得有关此类系统如何工作的独特新见解。我们的目标是位于新西兰以北约400公里处的太平洋“火环”中的兄弟火山。这座火山拥有世界上最活跃的海底热液系统之一。过去二十年来，它一直是国际研究的焦点，最终在 2018 年进行了科学钻探，以回收样本并在海底以下近 450 m 的深度进行测量。因此，它可以说是世界上同类火山中研究最透彻的。热液流体几乎在所有火山系统中循环，这种循环是固体地球与海洋之间化学和热交换的主要机制。沉入地壳的水被地表以下几公里处的热或熔融岩石加热，然后返回地表。化学物质与岩石进行交换，并可能浓缩在上升的液体中。熔岩本身是水和气体的额外来源。这些液体可以剧烈地排入海洋。当它们冷却并与海水混合时，浓缩在其中的元素会沉淀下来，有时会形成含有铜和金等金属的大型沉积物。对流体及其在海床和周围蚀变岩上的沉积物的研究表明： 喷发可能是集中的，也可能是扩散的；喷口流体可以有多种成分、温度和来源；随着火山的演化，流体的性质也会发生变化。然而，人们对钻探所能到达的几百米深度范围之外的情况知之甚少。因此，人们对深度流动路径的形状及其与下面的热或熔岩的关系仍然知之甚少。我们的实验涉及使用强大的发射器将电磁波发送到火山中，并使用海底的接收器和发射器后面拖曳的其他接收器来测量由此产生的电磁波动。我们的测量将对海底几公里深处的电阻率敏感。固体火山岩具有很高的电阻率，但当岩石开始融化时，其导电性会变得更强，从而产生很大的对比度。热热液的导电性甚至更高，尤其是当它们含盐时。位于海底或靠近海底的金属矿藏可以再次提高导电性。因此，我们提出的受控源电磁（CSEM）技术可用于对所有这些特征进行成像。三维 CSEM 成像现在已经可行，我们将首次在海底火山生成此类图像，从而实现前所未有的分辨率。我们将使用我们的电阻率图像来估计热源的大小、形状、温度和熔体含量热液系统下方；热液的温度和盐度以及它们在地壳内的路径形状；以及由此产生的矿藏的大小和形状。我们将把这些图像与国际合作者的结果结合起来，包括涉及通过火山发送声波的重大新实验，以及对其随时间演变的进一步钻探和计算机建模。我们的结果将显示下方热源的形状和内部结构以及该热源上方地壳的断层如何驱动热液循环模式，从而驱动地壳的化学变化。这种理解可以应用于地下结构不太为人所知的其他火山。我们还将确定循环海水和热源释放的流体对海底附近矿床形成的相对贡献，并与采矿业合作伙伴合作，评估对目前陆地上此类矿床勘探的影响。