海嶺拡大軸とオフィオライトにみられる熱水循環系

抄録

The heat and mass flux from hydrothermal activity along mid-ocean ridge crests has a relationship with the formation of oceanic crust and plays a significant role on material cycle in the ocean.
It is estimated that 1.7×10²⁰ J/yr of heat energy is transported by hydrothermal activity along mid-ocean ridges. The heat flux from one high temperature black smoker is estimated to be 250 MW and the energy amitted from the vent field with several tens of smokers in the area of several to several tens km² may be less than 10, 000 MW. On the other hand, the sporadic megaplume is believed to require 2-3 orders of magnitude larger heat flux than a normal plume.
Large amount of heat energy (2.0×10¹⁸ J) would be needed for the formation of three million tons of sulfide deposit. The sulfide deposits are distributed every two kilometers on average. These observations suggest that large-scale hydrothermal activity is more episodic than steady-state.
Fluid inclusions in the altered gabbro and plagiogranite in the oceanic crust and ophiolites have large salinity and temperature variations, which is interpreted as resulting from phase separation occurring in hydrothermal or magmatic fluids within the transition zone between the hydrothermal system and the magma chamber. The chemical flux by submarine hydro-thermal activity tends to be overestimated. It is important to estimate real net chemical flux from hot springs to the ocean.