Collaborative Research: Modeling hydrothermal recharge and outflow in oceanic crust analogs with sharp permeability gradients

通过洋中脊轴处的洋壳的流体循环是地球失去内部热量的主要机制。在海底，这种循环将热流体释放到深海中。这些热液地点通常拥有地球上其他地方找不到的生态系统和生命形式，并且被认为是地球上生命可能起源的地方之一。热液喷发通常发生在主要断层或断裂带处或附近，这表明洋壳中的这些断裂可以充当流体逸出的高渗透性管道。然而，目前尚不清楚地壳的这些破裂在多大程度上使流体能够进入并向下移动到海底并在那里被加热。这项研究使用模拟实验、3D 打印机和建模来探索洋中脊的流体循环如何自发组织并在高度裂缝和断层的地壳中传输热量。通过探索喷发点与主要构造特征之间的关系，该研究有助于我们了解地热过程和寻找海底新的热液点。 这项工作的更广泛影响包括研究和教育的整合以及三名早期职业调查员的支持，其中一名来自 EPSCoR 州（爱达荷州）的一家机构。 结果的应用范围从陆地地下水水文学到地热能、碳封存和石油工业。本研究采用数值和模拟实验来描述和定量解释非均质渗透率对地下流动几何形状和热量提取的影响。使用 3D 打印机，我们将生成海洋地壳的塑料类似物，其中包含一系列规则间隔的管子，这些管子将充当具有确定渗透性的流体通道。在该渗透性基质内，将创建具有规定宽度、倾斜度和更大渗透性（通过更宽的管道实现）的平面槽，代表通常围绕活动断层的损伤区域。打印的体积将被放置在含有葡萄糖和水的混合物的玻璃壁罐中。流体将从下方被加热以引发多孔对流。粒子图像测速、热致变色液晶和体积顶部和底部的温度传感器的组合将允许量化流体补给和排出的位置以及当渗透性对比度和槽的几何形状变化时对流系统的热量输出。 结果将与异质介质中多孔对流的数值模型进行比较，然后外推到自然条件。该研究将侧重于预测高渗透性断层带捕获和集中热液对流卷的条件。实验和理论相结合的方法将为研究位于主要断层系统旁边或主要地壳异质性附近的缓慢扩张的洋中脊上的目标热液地点提供很大帮助。

Fluid circulation through the oceanic crust at the axis of mid-ocean ridges is a primary mechanism through which the Earth loses its internal heat. At the seafloor, this circulation releases hot fluids into the deep ocean. These hydrothermal sites typically host ecosystems and life forms found nowhere else on the planet and are thought to be one of the places on Earth where life may have originated. Hydrothermal fluid venting often occurs at or near major fault or fracture zones, suggesting that these breaks in the ocean crust can act as highly permeable conduits for fluids escape. It is unclear, however, to what extent these breaks in Earth's crust enable fluids to enter and move downward into the seafloor where they get heated. This research uses analog experiments, using a 3-D printer, and modeling to explore how fluid circulation at mid-ocean ridges spontaneously organizes itself and transports heat in highly fractured and faulted crust. By allowing exploration of the relation between venting sites and major tectonic features, the research facilitates our understanding of geothermal processes and the search for new hydrothermal sites on the seafloor. Broader impacts of the work include integration of research and education and support of three early career investigators, one from an institution in an EPSCoR state (Idaho). Results have applications ranging from terrestrial groundwater hydrology to geothermal energy, carbon sequestration, and the oil industry.This research employs numerical and analog experiments to describe and quantitatively explain the effect of heterogeneous permeability on subsurface flow geometry and heat extraction. Using a 3-D printer, we will generate plastic analogs of oceanic crust, containing a series of regularly spaced tubes that will act as fluid pathways of defined permeability. Within this permeable matrix, a planar slot of prescribed width, inclination, and greater permeability (achieved through wider tubes) will be created, representing the damage zone that typically surrounds active faults. The printed volume will be placed in a glass-walled tank containing a mixture of glucose and water. The fluid will be heated from below to initiate porous convection. A combination of particle image velocimetry, thermo-chromic liquid crystals, and temperature sensors at the top and bottom of the volume will allow quantification of the locations of fluid recharge and discharge and the heat output of the convective system as the permeability contrast and geometry of the slot is varied. Results will be compared to numerical models of porous convection in heterogeneous media and then extrapolated to natural conditions. The research will focus on predicting the conditions under which high-permeability fault zones can trap and focus hydrothermal convection rolls. The combined experimental and theoretical approach will greatly inform the investigation of targeted hydrothermal sites on slow-spreading mid-ocean ridges that sit next to major fault systems or near major crustal heterogeneities.