Cross-hole tracer experiment reveals rapid fluid flow and low effective porosity in the upper oceanic crust
Cross-hole tracer experiment reveals rapid fluid flow and low effective porosity in the upper oceanic crust
复制标题
跨孔示踪实验揭示了上洋壳中流体快速流动和低有效孔隙度
DOI：
10.1016/j.epsl.2016.06.048
复制
发表时间：
2016
影响因子：
5.3
通讯作者：
K. Becker
中科院分区：
文献类型：
--
作者：
N. Neira;J. Clark;A. Fisher;C. Wheat;R. Haymon;K. Becker
许多现场，实验室和模拟研究探索了海底热液循环过程中的流体，热量和溶质的流动，但它一直具有挑战性，以确定自然系统内的传输速率和流动方向。在这里，我们提出的结果，从第一个跨孔示踪剂实验在上大洋地壳，使用四个海底钻孔观测站配备了自主采样器，跟踪运输的溶解示踪剂（六氟化硫，SF6）注入到脊侧翼热液系统。在示踪剂注入后的前三年，SF6通过玄武质含水层向北和向南迁移。所观察到的示踪剂传输速率为10.2 -3米/天，比从热和化学观测中推断出的并用耦合流体-热流模拟计算出的整体流量大几个数量级。综上所述，这些结果表明，上火山地壳的有效孔隙度，通过大量的示踪剂被运输是<1%，与流体快速流动沿着几个连接良好的通道。这是一致的异质性（分层，断层，和/或断裂）性质的火山上洋壳。
Numerous field, laboratory, and modeling studies have explored the flows of fluid, heat, and solutes during seafloor hydrothermal circulation, but it has been challenging to determine transport rates and flow directions within natural systems. Here we present results from the first cross-hole tracer experiment in the upper oceanic crust, using four subseafloor borehole observatories equipped with autonomous samplers to track the transport of a dissolved tracer (sulfur hexafluoride, SF6) injected into a ridge-flank hydrothermal system. During the first three years after tracer injection, SF6was transported both north and south through the basaltic aquifer. The observed tracer transport rate of ∼2–3 m/day is orders of magnitude greater than bulk rates of flow inferred from thermal and chemical observations and calculated with coupled fluid-heat flow simulations. Taken together, these results suggest that the effective porosity of the upper volcanic crust through which much tracer was transported is <1%, with fluid flowing rapidly along a few well-connected channels. This is consistent with the heterogeneous (layered, faulted, and/or fractured) nature of the volcanic upper oceanic crust.