Sensitivity of heat flow and gravity to the mechanism of sea-floor spreading

Idealized mathematical models have been constructed to show that gravity, heat flow, and regional topography cannot be expected to distinguish between sea-floor spreading where new lithosphere is intruded into a narrow zone and sea-floor spreading where new lithosphere originates from a broad upwelling. A reasonable fit is obtained between observed and theoretical gravity and regional topography for the mid-Atlantic ridge. The observed inverse relation between topographic roughness and spreading rate can be explained by the proximity of isotherms to the surface at higher spreading rates. The central rift of the Gorda rise and the mid-Atlantic ridge is too large to be compensated isostatically but may be compensated by hydraulic loss in the upwelling due to viscosity.