The Study On Models For Formation Of Megaplume Flow In Modern Seafloor Hydrothermal Activity

Seafloor hydrothermal activity system develops up to be an international hot point for study in recent 10 years. The mechanism of formation for megaplume flow system that has a big vent or consists of more vents becomes an important and unsolved subject, because of formation of massive sulphides from its mega hydrothermal plume and the ignorance of formation processes.In the paper, directions and results of the study on modern seafloor hydrothermal activity are analyzed and summarized firstly. Traditional mathematic models are analyzed and their pros and cons are concluded.The basic mathematic model is built to simulate normal black smoker system and the formation of megaplume and to solve the temperature, period and maximal mass fluid rate when megaplume forms. The effects of main parameters like temperature of hot-source, permeability, volume of reaction-zone and area of discharge-zone on the formation of megaplume are discussed. Main conclusions are as follows. A normal black smoker system can evolve into a megaplume eruption. In fact, megaplume hydrothermal eruption will occur in two or three years. The temperature of the hot source must exceed 500℃, while the highest temperature of eruption fluid is about 413℃. If the temperature of the hot source is higher than 500℃, the critical period for megaplume's formation can be obviously curtailed to be less than 1 year, while the critical temperature and the maximal mass fluid rate are nearly invariable. As the permeability increases, the maximal mass fluid rate increases gradually close to a steady value.The second model adds an embranchment which represents lower-temperature downward permeating seawater to the first model and simulates the dilution effects of permeating cold seawater to hydrothermal fluid. Conclusions are found after analyzing the solutions as follows: Permeating cold seawater can hardly invade the black smoker to dilute the hot fluid. The embranchment zone may become the next bigger discharge-zone when the hot fluid discharges in high speed, which may be...