Multi-Phase Flow in High-Temperature Hydrothermal Systems at Oceanic Spreading Centres — A Case Study at the East Pacific Rise

海洋扩张中心的热液系统是地球质量和能量循环的关键组成部分。当海水进入洋壳并被岩浆作用加热时，海底就会形成温泉。热的热液具有高度的反应性，促进了洋壳和深海环境之间的热和化学交换。这种交换为生物群落提供了营养，形成了具有经济意义的矿床，并有助于全球碳循环。尽管海底热液系统被研究了40多年，但它们的许多特征仍然不明确。当盐水被强烈加热时，它会分离成高密度、高盐度的盐水相和低密度、低盐度的蒸汽相。在热液喷口流出的流体中测得的盐度变化，特别是在岩浆活动的热输入之后，是这些相变和相分离的主要指标。在现实的三维(3-D)数值模型中，还没有研究这些相在洋壳内的路径和流动动力学。特别令人感兴趣的是盐水的流动，因为流体和岩石之间的相互作用取决于盐度(石英的溶解和沉淀、金属的运输)。目前还不清楚是什么过程控制了快速扩张中心的热液喷发场的位置。为了揭示隐藏在洋壳中的热液过程，该项目将结合地震数据分析、数值模拟和喷口流体测量的时间序列。该项目的中心是一项详细的案例研究，目标是东太平洋海隆位于北纬9°50‘的非常详细的研究区段，在那里，高分辨率地震数据集揭示了大洋地壳的结构细节(例如，可能是热液流体通道的高孔隙度地带)。地震数据还显示了下伏岩浆系统的特征，如深度和熔体分数沿山脊轴线的变化。这些地震信息将被考虑到一个新的咸水热液系统三维数值模型中，该模型将在项目的第一部分开发。数值结果将与海底的观测和测量结果进行比较。该项目旨在建立喷口区域分布、喷口流体温度和盐度、海底地壳结构和岩浆系统特征之间的因果联系。预期的结果不仅将揭示海底热液系统的动力学，而且还将揭示它们与洋壳内的岩浆过程和水文结构的相互作用。

Hydrothermal systems at oceanic spreading centres are a key component in the Earth’s mass and energy cycles. Hot springs at the seafloor form when seawater enters the oceanic crust and is heated up by magmatic processes. Hot hydrothermal fluids are highly reactive and facilitate a thermal and chemical exchange between oceanic crust and deep sea environment. This exchange provides the nutrition for biological communities, forms economically interesting ore deposits, and contributes to the global carbon cycle.Although submarine hydrothermal systems are investigated for more than four decades, are many of their characteristics still ambiguous. When saltwater is strongly heated, it separates into a high-density, high-salinity brine phase and low-density, low-salinity vapour phase. Measured salinity variations in fluids exiting at hydrothermal vents, especially after heat input from magmatic activity, are the main indicator for these phase transitions and phase separations. The pathways and flow dynamics of these phases within the oceanic crust have not been investigated in a realistic, three-dimensional (3-D) numerical model. Of particular interest is the flow of saline brines, because interactions between fluid and rock depend on salinity (dissolution and precipitation of quartz, transport of metals). It is also unclear, which processes control the location of hydrothermal vent fields at fast spreading centres.To shed light on the hydrothermal processes hidden within the oceanic crust, this project will combine seismic data analysis, numerical modelling, and time series of vent fluid measurements. The central point of the project is a detailed case study targeting the extraordinary well-studied section of the East Pacific Rise at 9º 50’ N, where a high-resolution seismic data set reveals structural details of the oceanic crust (e.g. high-porosity zones that may be hydrothermal fluid pathways). The seismic data also shows characteristics of the underlying magmatic system such as variations in depth and melt fraction along the ridge axis. These seismic information will be considered in a new 3-D numerical model for saltwater hydrothermal systems, which will be developed in the first part of the project. The numerical results will be compared against observations and measurements at the seafloor. The project aims at establishing causal links between vent field distributions, vent fluid temperature and salinity, structure of the underlying oceanic crust, and characteristics of the magmatic system. The expected results will not only reveal the dynamics of submarine hydrothermal systems but also their interaction with magmatic processes and hydrological structures within the oceanic crust.