Fluid Flow and Fluid‐Rock Interaction Within Ocean Crust: Reconciling Geochemical, Geological, and Geophysical Observations
Fluid Flow and Fluid‐Rock Interaction Within Ocean Crust: Reconciling Geochemical, Geological, and Geophysical Observations
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洋壳内的流体流动和流体-岩石相互作用：协调地球化学、地质和地球物理观测
DOI：
10.1029/144gm07
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
A. Fisher
中科院分区：
文献类型：
--
作者：
W. Bach;S. Humphris;A. Fisher
流体流动控制着海底热液系统中的热量和质量传输，并对海洋地壳深部微生物生态系统的性质和分布产生控制作用。我们综合了DSDP和ODP关键钻孔的地球物理、岩石学和地球化学数据，以评估海洋岩石圈中的流体循环路径、流体流速和流体-岩石相互作用。流体进入岩石圈深部受断层和韧性剪切带的发育、岩浆向地壳浅层的注入以及脆性破裂前缘向下传播进入热岩的控制。海脊侧翼的海水循环取决于地壳渗透性结构、热量供应以及地壳含水层与上覆海洋之间是否存在开放通道。钻孔岩石代表不同年龄和地质背景的玄武质地壳，表现出统一的一级蚀变阶段序列。氧化蚀变和开放的海水循环的早期阶段之后，在不同的条件下限制流体循环。蚀变程度高的区域往往对应于渗透率高的区域，这表明岩石蚀变和矿物沉淀并不能完全封闭大规模的、渗透性最强的流体通道。在几十到几百米的尺度上，流体流动受渗透性岩性分布的控制：角砾岩、破裂的枕状玄武岩和断层充当含水层，而相当大面积的大量流动可能充当流体流动屏障。流动边界、枕状边缘和大的冷却裂纹是米尺度下的主要流体通道，而在最小尺度下，微裂纹和晶界控制流体流动。因此，流体流动是高度渠道化的，只有一小部分基底与海洋相通。远离这些主要流体管道的流体-岩石相互作用主要是扩散控制的，使得基底的最大部分对于依赖于循环流体的营养供应的微生物来说不太理想。
Fluid flow governs heat and mass transport in subseafloor hydrothermal systems and exerts control on the nature and distribution of deep microbial ecosystems in oceanic crust. We have integrated geophysical, petrographical, and geochemical data from key DSDP and ODP drill holes to assess fluid circulation pathways, fluid flow rates, and fluid-rock interaction in the oceanic lithosphere. Fluid ingress into the deep lithosphere is controlled by the development of faults and ductile shear zones, magmatic injection into the shallow crust, and downward propagation of a front of brittle fracturing into hot rock. Seawater circulation in the ridge flanks is governed by the crustal permeability structure, the availability of heat, and the existence of open pathways between the crustal aquifer and the overlying ocean. Rocks from drill holes representing basaltic crust of various ages and geological settings exhibit a uniform first-order sequence of alteration stages. An early stage of oxidative alteration and open seawater circulation is followed by restricted fluid circulation under varying conditions. Zones of high degrees of alteration often correspond to zones of high permeability, indicating that rock alteration and mineral precipitation do not completely seal the large-scale, most-permeable fluid pathways. On the scale of tens to hundreds of meters, fluid flow is controlled by the distribution of permeable lithologies: breccias, fractured pillow basalts and faults act as aquifers, while massive flows of considerable areal extent may act as fluid flow barriers. Flow boundaries, pillow margins and large cooling cracks are the main fluid conduits at the meter-scale, while at the smallest scale, micro-cracks and grain boundaries control fluid flow. Hence, fluid flow is highly channelized and only a small fraction of basement communicates with the oceans. Fluid-rock interactions away from these main fluid conduits are dominantly diffusion-controlled, making the largest fraction of basement less desirable for microorganisms that rely on supply of nutrients by circulating fluids.