On the Thermal Balance of a Mid-Ocean Ridge

Abstract

The northernmost expressions of the East Pacific Rise spreading centre, the Juan de Fuca Ridge and Explorer Trough, have unusual heat-flow distributions. Crestal values are only moderately high, but flank areas that are models of undisturbed sedimentation have mean heat flows near 7 HFU (290 mW m−2). The values in these areas retain considerable scatter, but the detailed distribution is close to the opposite of that expected from conductive heat-flow refraction. The high mean values confirm that sea-floor spreading occurs by the upwelling of hot (magma temperature) material. The low crestal measurements and the non-refractive scatter in the flank areas strongly suggest that hydrothermal circulation is the dominant heat transfer process in fresh crestal material. Much of the heat loss from the new lithospheric material must occur through open circulation near the ridge crest and is never reflected in measurements of surface conduction.