Hybrid shallow on-axis and deep off-axis hydrothermal circulation at fast-spreading ridges
Hybrid shallow on-axis and deep off-axis hydrothermal circulation at fast-spreading ridges
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DOI：
10.1038/nature13174
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发表时间：
2014-04-24
期刊：
影响因子：
64.8
通讯作者：
Devey, Colin W.
中科院分区：
文献类型：
--
作者：
Hasenclever, Joerg;Theissen-Krah, Sonja;Devey, Colin W.
海洋扩张中心的热液流约占海洋所有热通量的10%（1，2），并控制着年轻海洋板块的热结构。它还影响海洋和地壳化学，为化学合成生态系统提供基础，并在整个地球历史上形成了块状硫化物矿床。尽管如此，如何以及在什么条件下提取热量，特别是从下地壳提取热量，仍然很不清楚。在这里，我们提出了高分辨率，全地壳，二维和三维模拟的热液流下的快速扩展的山脊，预测存在两个相互作用的流动组件，由不同的物理机制控制，合并以上的熔体透镜，饲料山脊为中心的喷口网站。浅轴上的流动结构的发展，由于水的热力学性质，而更深的离轴流动强烈地塑造地壳渗透性，特别是脆韧性转变。大约60%的排放流体质量在轴上由围绕热的热羽流的温暖（高达300摄氏度）的补给流补充，其余40%左右是在距离轴数公里以外的较冷和较广泛的补给流，向海脊输送热的（500-700摄氏度）深根离轴流。尽管它对总质量通量的贡献较低，但这种深离轴流携带了在脊轴处释放的约70%的热能。这两种流动成分的组合解释了地壳的地震热结构，并调和了以前不相容的模型，这些模型倾向于较浅的轴上（3-5）或较深的离轴热液循环（6-8）。
Hydrothermal flow at oceanic spreading centres accounts for about ten per cent of all heat flux in the oceans(1,2) and controls the thermal structure of young oceanic plates. It also influences ocean and crustal chemistry, provides a basis for chemosynthetic ecosystems, and has formed massive sulphide ore deposits throughout Earth's history. Despite this, how and under what conditions heat is extracted, in particular from the lower crust, remains largely unclear. Here we present high-resolution, whole-crust, two-and three-dimensional simulations of hydrothermal flow beneath fast-spreading ridges that predict the existence of two interacting flow components, controlled by different physical mechanisms, that merge above the melt lens to feed ridge-centred vent sites. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittleductile transition. About 60 per cent of the discharging fluid mass is replenished on-axis by warm (up to 300 degrees Celsius) recharge flow surrounding the hot thermal plumes, and the remaining 40 per cent or so occurs as colder and broader recharge up to several kilometres away from the axis that feeds hot (500-700 degrees Celsius) deep-rooted off-axis flow towards the ridge. Despite its lower contribution to the total mass flux, this deep off-axis flow carries about 70 per cent of the thermal energy released at the ridge axis. This combination of two flow components explains the seismically determined thermal structure of the crust and reconciles previously incompatible models favouring either shallower on-axis(3-5) or deeper off-axis hydrothermal circulation(6-8).