High-resolution three-dimensional simulations of mid-ocean ridge hydrothermal systems
High-resolution three-dimensional simulations of mid-ocean ridge hydrothermal systems
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DOI：
10.1029/2008jb006121
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发表时间：
2009-07-18
影响因子：
3.9
通讯作者：
Heinrich, C. A.
中科院分区：
文献类型：
--
作者：
Coumou, D.;Driesner, T.;Heinrich, C. A.
高分辨率数值模拟给出了与黑烟水热系统相关的热对流的三维结构的清晰见解。我们给出的一系列模拟表明，在海洋中脊扩展轴处的预期热通量下，上升流集中在圆形的管状区域，大部分补给发生在近轴区域。补充液的温度相对较高。在这种配置中，系统最大化其热输出，这可以被证明与流体属性的非线性有关。此外，我们还给出了不同渗透率情况下的一系列模拟。这表明，当渗透率反差适中时，对流保持了这种管状流体流动结构。渗透率反差只在对流的早期、未成熟阶段、高渗透区集中上升流、低渗透区集中下降流阶段对流型起主导作用。在对流的早期阶段，扩散喷口可能会出现，它们看起来与自然系统中的扩散喷口非常相似。最后，将渗透率定义为温度的函数的模拟表明，脆韧条件很可能发生在不低于650摄氏度的温度下。在较低的脆韧转变温度下，系统无法带走从岩浆室输送的热量，并且喷口温度大大低于400摄氏度。这一结果与根据岩石力学研究和大洋岩石圈地震所作的脆韧转变温度估计值一致。
High-resolution numerical simulations give clear insights into the three-dimensional structure of thermal convection associated with black-smoker hydrothermal systems. We present a series of simulations that show that, at heat fluxes expected at mid-ocean ridge spreading axes, upflow is focused in circular, pipe-like regions, with the bulk of the recharge taking place in the near-axial region. Recharging fluids have relatively warm temperatures. In this configuration, the system maximizes its heat output, which can be shown to be linked to nonlinearity in the fluid properties. Furthermore, we present a series of simulations with different permeability scenarios. These show that when permeability contrasts are moderate, convection maintains this pipe-like fluid flow structure. The permeability contrast has a dominant effect on flow patters only at early, immature, stages of convection, focussing upflow in high-permeability regions and downflow in low-permeability regions. In such early stages of convection, diffusive vent styles can emerge, which look remarkably similar to diffuse vent fields in natural systems. Finally, simulations in which permeability is defined as a function of temperature indicate that the brittle-ductile condition is likely to occur at temperatures not lower than 650 degrees C. At lower brittle-ductile transition temperatures, the system cannot remove the heat delivered from the magma chamber and vent temperatures are substantially lower than 400 degrees C. This result is in agreement with estimates of the brittle-ductile transition temperature from rock-mechanical studies and the occurrence of earthquakes in the oceanic lithosphere.