Heat flow from the Mid-Ocean Ridges and sea-floor spreading

Abstract

Observations of heat flow, topographic elevation and topographic slope are examined in the light of the hypothesis of ridge formation by ocean-floor spreading. By normalizing the distance of observations from the ridge axis in terms of the spreading rate, a large amount of data from all parts of the ridge system can be used to derive the pattern of heat flow with greater confidence than here-to-fore obtained. This analysis shows that the shape of the normalized anomaly of high heat flow over the ridge is independent of spreading rate, however, the amplitude of this anomaly over the fast-spreading Pacific ridges (3–6 cm/year) is generally 0.5 μcal/cm 2sec larger than that over the Atlantic and Indian Ocean Ridge which are spreading at a slower rate (1–2 cm/year). More than 60% of the heat lost over the ridges in excess of the adjacent basin heat loss takes place in a narrow zone near the axis, corresponding to the part of the ridge that has been created in the last 6 million years. There is also a nearly linear relation between spreading rate and ridge topographic slope. The normalized slope, however, decreases slightly with increasing spreading rate. Simple mechanical models of ocean-floor spreading such as a thick plate cooling as it moves away from the axis or a thin plate moving over a shallow, near isothermal zone do not adequately explain the pattern of heat flow and topographic slopes derived in this paper. A complex model such as a thin crustal layer moving over a broad stagnation zone could fit the observed data. However, more definitive geophysical data are required to determine the details of this type of model.