The TAG hydrothermal field

Abstract

THERE is abundant evidence that seawater penetrates, and circulates within, the oceanic crust at active spreading centres. Low heat flow values from ridge crests imply that heat must be removed locally by water circulation1–6. Furthermore, hydrous metamorphosed oceanic crust and oceanic serpentines, which required voluminous quantities of water during their formation7–9, also have isotopic compositions which indicate that the isotopic sources had low δ18O values, such as are found in seawater10. The tectonic setting of strike–slip and normal faulting along the rift valley scarps of oceanic ridges is conducive to the penetration of dense, cold water down the fractures, the heating of the water at depth, and the exhalation of the less dense hydrothermal water as submarine springs along fracture systems.