The basic mathematic model for normal black smoker system and hydrothermal megaplume

The tube model to simulate a normal black smoker system has been built.Darcy flow equation,Ergun equation and turbulent pipe flow equation are respectively used to describe the dynamic processes of different key parts in a hydrothermal circulation system.Meanwhile,a convection-diffuse equation for a temperature field is used to describe the exchange of heatenergy and temperature variety.Combining those equations,using efficient mathematic algorithms and program ming in Mat lab language,the variation curves of temperature,pressure and mass fluid rate by the time are achieved.Then,developing hot and pressure balances in the black smoker system are analyzed.On the basis of the model of normal black smoker system,a megaplume formation model is further built.As an instance,the hydrothermal venting plume on the Juande Fuca Ridge has been simulated and the simulated results are fairly consistent with Bakers imputed data on surveying.On the basis of the above productive simulations,a series of conditions for megaplumes for mation and the effect of main parameters on the megaplume forming period,temperature and maximum mass fluid rate were systemly discussed.Main conclusions are as follows:The normal black smoker system can evolve to a megaplume eruption.In fact,hydrothermal discharge pass way can be blocked up with hydrothermal sediments during black smoker period,leading to hydrot hermal fluid accumulating,temperature rising and the buoyancy pressure increasing under the seafloor.After 2~3 a,the megaplume hydrothermal eruption will occurif the buoyancy pressure increase is high enough to break through the blockage.At the same time,the highest temperature of eruption fluid may be high up to 413℃,fairly consisting with the surveyed data,and the temperature of the heat source must exceed 500℃.If the temperature of the heat source increases higher 500℃,the critical period for the megaplumes formation can be obviously curtailed to be less than 1 a,while the critical tem perature and the maximum mass fluid rate are nearly invariable.As the permeability increases,the maximum mass fluid rate increases gradually close to a steady value.