Study on the influence of the structure of oceanic crust permeability on the hydrothermal convection-Based on thermodynamic modelling

Extreme environment of the ocean floor makes numerical modelling an effective way to study the convection and mineralization of the hydrothermal deposits. In this paper, thermodynamic modelling is used to study the influence of single factor (permeability) on the geometry of hydrothermal convection and output parameters (venting temperature and heat flux). Simulation results show that the average permeability of oceanic crust is inversely and positively correlated with venting temperature and output heat flux, which is consistent with the analytical solution of Darcy fluid convection. In the case with localized heat source, the vertical increase of permeability reduces the size of hydrothermal plumes, without any horizontal deviation; by contrast, the horizontal variation of permeability within oceanic crust does deviate the geometry of hydrothermal circulation laterally, and only in certain ranges of horizontal permeability variation the significant deviation of hydrothermal plumes toward high permeability areas will occur, which is consistent with the non-existence of hydrothermal venting on the termination of detachment faults on slow-ultraslow spreading ridges. Taking the TAG hydrothermal field on 26 degrees N, Mid-Atlantic Ridge as an example, hydrothermal upwelling in the oceanic crust will be unavoidably affected by adjacent high permeability fault zone, but it will not cause a significant deviation, so that hydrothermal vents finally develop on the hanging wall of the detachment.