Collaborative Research: Modeling Hydrothermal Recharge and Outflow in Oceanic Crust Analogs with Sharp Permeability Gradients

在大洋中脊轴处通过洋壳的流体循环是地球失去其内部热量的一个主要机制。在海底，这种环流将热流体释放到深海中。这些热液区通常拥有地球上其他地方找不到的生态系统和生命形式，被认为是地球上生命可能起源的地方之一。热液流体的喷发经常发生在主要断层或断裂带或其附近，这表明这些海洋地壳的断裂可以作为流体逃逸的高渗透性管道。然而，目前还不清楚这些地壳断裂在多大程度上使流体能够进入并向下移动到海底，在那里它们被加热。这项研究使用模拟实验，使用3D打印机和建模来探索大洋中脊的流体循环如何自发地组织起来，并在高度断裂和断层的地壳中传输热量。通过探索火山口与主要构造特征之间的关系，这项研究有助于我们了解地热过程和寻找海底新的热液地点。 这项工作的更广泛影响包括研究和教育的整合以及对三名早期职业调查人员的支持，其中一名来自EPSCoR州（爱达荷州）的一个机构。 研究结果的应用范围从陆地地下水水文地热能，碳封存，和石油industry.This研究采用数值模拟实验来描述和定量解释的非均匀渗透性对地下水流的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模拟物，其中包含一系列规则间隔的管道，这些管道将充当具有特定渗透性的流体通道。在这个渗透性基质中，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。将打印的体积置于装有葡萄糖和水混合物的玻璃壁罐中。流体将从下方被加热以启动多孔对流。粒子图像测速仪，热致变色液晶，和温度传感器在顶部和底部的体积的组合将允许量化的位置的流体补给和排放和对流系统的热输出的渗透性对比度和几何形状的槽是不同的。 结果将比较非均匀介质中的多孔对流的数值模型，然后外推到自然条件。研究将侧重于预测高渗透性断层带能够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大大有助于调查位于主要断层系统旁边或主要地壳不均匀性附近的缓慢扩张的洋中脊上的目标热液地点。

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.