Permeability of the Lucky Strike deep-sea hydrothermal system: Constraints from the poroelastic response to ocean tidal loading
Permeability of the Lucky Strike deep-sea hydrothermal system: Constraints from the poroelastic response to ocean tidal loading
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DOI：
10.1016/j.epsl.2014.09.049
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发表时间：
2014-12
影响因子：
5.3
通讯作者：
T. Barreyre;J. Escartín;R. Sohn;M. Cannat
中科院分区：
文献类型：
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作者：
T. Barreyre;J. Escartín;R. Sohn;M. Cannat
我们使用潮汐载荷和诱导地下水流响应之间的时间延迟来约束中大西洋海岭上的Lucky Strike热液场的孔隙弹性行为和渗透率。我们证明，高温（T> 200° C）出口流体排放记录从四个热液站点在整个领域是高度一致的同期获得的底部压力记录在潮汐时期，与热响应滞后压力平均为155°（5.3小时）在所有站点的半日（M2）的频率超过三年的观察期。在海洋潮汐载荷的一维孔隙弹性模型中，这种相位滞后对应于高渗透性系统，其中海底的孔隙压力扰动从海底界面快速向下传播，直到它们遇到渗透性边界。我们的研究结果表明，在幸运罢工领域，这种潮汐抽水主要限于10600米厚的喷出层（即地震层2A）。在一组合理的基质弹性参数下，压力和出口流体温度之间的滞后时间为2.53 h，这与有效基质渗透率为2.10 - 10 m2和喷出层内平均垂直流速为2.02 m/s是一致的。我们的研究结果反对海底和轴向岩浆房之间的整个地壳部分的潮汐泵送（在3.4 kmbsf），因为这种情况下需要不切实际的高有效渗透率（10 - 9 m2）和平均垂直流速（10.15 m/s）在这个深度范围内。我们的有效渗透率估计喷出层大致与以前的结果是一致的，并表明，流量必须引导离散的渗透性途径（如断层，裂缝），通过喷出火山层切割。
We use the time delay between tidal loading and the induced subsurface flow response to constrain the poroelastic behavior and permeability of the Lucky Strike hydrothermal field on the Mid-Atlantic Ridge. We demonstrate that high-temperature (T> 200° C) exit-fluid discharge records from four hydrothermal sites across the field are highly coherent with contemporaneously acquired bottom pressure records at tidal periods, with the thermal response lagging pressure by∼ 155°(5.3 h) on average across all sites for the semi-diurnal (M2) frequency over a three-year observation period. In a one-dimensional poroelastic model of ocean tidal loading this phase lag corresponds to a high-permeability system where pore pressure perturbations at the seafloor rapidly propagate downward from the seafloor interface until they encounter a permeability boundary. Our results suggest that at the Lucky Strike field this tidal pumping is largely restricted to the∼ 600 m thick extrusive layer (ie, seismic layer 2A). Under a plausible set of matrix elastic parameters, the∼ 5.3 h lag between pressure and exit-fluid temperature is consistent with an effective matrix permeability of∼ 10− 10 m 2 and an average vertical flow velocity of∼ 0.02 m/s within the extrusive layer. Our results argue against tidal pumping of the entire crustal section between the seafloor and the axial magma chamber (at∼ 3.4 kmbsf) because this scenario requires unrealistically high effective permeabilities (∼ 10− 9 m 2) and average vertical flow velocities (∼ 0.15 m/s) over this depth range. Our effective permeability estimate for the extrusive layer is broadly consistent with previous results, and indicates that flow must be channeled in discrete permeable pathways (eg, faults, fissures) that cut through the extrusive volcanic layer.