Study on the influence of bathymetry on hydrothermal convection under mid-ocean ridges: Based on the spatial variation of overlying pressure of seawater
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摘要: 洋中脊热液活动多产生于不同扩张速率洋中脊的局部高地形区域，基于达西流体充填的孔隙−弹性热力学模型可以直观、有效地模拟出洋壳内部热液对流的形态、温度结构和喷发位置等信息。数值模拟结果和所得解析模型表明：不同规模的洋底地形起伏会对洋壳内部的热液对流形态产生不同程度的影响，高地形规模越大，起伏程度越大，下伏热液羽向地形高点的偏移就越明显。通过结合东太平洋海隆9°17′N热液区和大西洋洋中脊Lucky Strike热液区实际的跨轴水深分布，也可获得与二者实际喷发位置相吻合的模拟结果。地形起伏相关的洋中脊热液喷发模型揭示洋底低地形及其下伏渗透性洋壳表现为主要的海水充注区域，而高地形由于上覆压力的减小，使其成为汇集热液释放和喷发的主要区域。Abstract: Hydrothermal venting systems mostly develop on the localized bathymetric highs of mid-ocean ridges with different spreading rates, and porous-elastic thermodynamic numerical models, which is filled with Darcian fluid can intuitively model the geometry, temperature structure and venting location of the hydrothermal systems in oceanic crust. Simulation results and the experimental-analytical model reveal that bathymetric highs with different sizes show a varied influence on the geometry of hydrothermal convection, the greater and wider bathymetric highs, the greater deflection of underlying plume to the bathymetric highs. Adopting the cross-axis bathymetry of the EPR 9°17′N and Lucky Strike hydrothermal fields into the model, our simulations produce vents fitting the realistic location of these two fields well. Finally, our schematic model for bathymetric relief deflecting underlying plumes indicates that the lower bathymetry and its underlying porous oceanic crust act as the main recharge zone, while the bathymetric high focuses the most of the discharge hot fluid due to the reduce of the overlying pressure of seawater.
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Key words:
- hydrothermal convection /
- numerical modelling /
- bathymetric relief /
- seawater pressure /
- Darcy’s law
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图 1 模型设置与边界条件
a. 上覆压力分布与其所代表的海底地形起伏示意图;b. 模型尺寸与边界条件
Fig. 1 Model setup and boundary conditions
a. Schematic sketch for the distribution of overlying pressure and bathymetric relief; b. model size and boundary conditions
图 2 数值模拟结果
a. 2 000 m×50 m高地形数值模拟结果; b. 2 000 m×100 m高地形数值模拟结果; c. 4 000 m×50 m高地形数值模拟结果; d. 4 000 m×100 m高地形数值模拟结果
Fig. 2 Simulation results
a. Simulation with a bathymetric high of 2 000 m×50 m; b. simulation with a bathymetric high of 2 000 m×100 m; c. simulation with a bathymetric high of 4 000 m×50 m; d. simulation with a bathymetric high of 4 000 m×100 m
图 3 热液羽偏移程度与地形高度的关系
a. 热液羽偏移距离与地形高度的关系; b. 热液羽偏移角度与地形高度的关系
Fig. 3 Relationship between deviation of fluid plumes and height of bathymetric highs
a. Relationship between deviation distance of plumes and height of bathymetric highs; b. relationship between deviation degree of plumes and height of bathymetric highs
图 4 热液羽偏移程度实验模型
a. 热液羽偏移距离实验模型; b. 热液羽偏移角度实验模型
Fig. 4 Experimental model of the deviation of plumes
a. Model of the deviation distance of plumes; b. model of the deviation degree of plumes
图 5 基于EPR 9°17′N热液区地形剖面的数值模拟结果
a. EPR 9°17′N热液区跨轴剖面; b. 基于水深剖面计算的海水压力剖面; c. 稳态数值模拟结果，离轴距离为0代表洋脊轴的位置
Fig. 5 Simulation result based on the bathymetric profile of the EPR 9°17′N vent
a. Cross-axis profile of EPR 9°17′N vent; b. calculated seawater pressure profile; c. running result in steady-state, distance=0 means the location of ridge axis
图 6 基于Lucky Strike热液区地形剖面的数值模拟结果
a. Lucky Strike热液区跨轴剖面; b. 基于水深剖面计算的海水压力剖面; c. 稳态数值模拟结果，离轴距离为0代表洋脊轴的位置
Fig. 6 Simulation result based on the bathymetric profile of the Lucky Strike vent
a. Cross-axis profile of Lucky Strike vent; b. calculated seawater pressure profile; c. running result in steady-state, distance = 0 means the location of ridge axis
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