Controls on the physics and chemistry of seafloor hydrothermal circulation

Abstract
Low temperature diffuse hydrothermal circulation is a natural consequence of the cooling of the oceanic lithosphere. Diffuse flow is expected to be ubiquitous, and will be present both within mid–ocean ridge crest axial zones of young age (0–1 Ma), and also on the older ridge crest flanks and limbs. If underlying thermal models are correct, hydrothermal circulation should persist for oceanic lithosphere of age 0–65 Ma, and is present over half the total area of the ocean basins. By using numerical models of hydrothermal circulation in cracked permeable media, we show qualitatively how diffuse flow is an intrinsic feature of high temperature axial (–1 Ma) hydrothermal systems, and is not restricted to older (more than 1 Ma) lithosphere. This is in agreement with our field observations which suggest that in such high temperature vent fields the greatest part of the heat and volume flux is due to lower temperature diffuse flow, rather than high temperature black smoker venting.