Oceanic bathymetry profiles flattened by radiogenic heating in a convecting mantle

Abstract

Reliable measurements of both ocean floor topography and heat flow indicate a linear dependence on the square root of the age, t, of the ocean floor for t ≲90 Myr (ref. 1) or about half the age of the large oceanic plates. Consequently, major topographic and heat flow variations perpendicular to mid-ocean ridge axes are generally believed to be thermally induced and associated with contraction of the lithosphere as it moves away from the ridges^1–4. For t>90 Myr, measurements of bathymetry (but not of heat flow) indicate a systematic departure from a t^½ relationship reaching almost 20% at the oldest ages. We present here numerical calculations of thermally induced topography above two-dimensional convection cells which are heated partially from within and partially from below. These exhibit the same general features as oceanic bathymetry and we suggest that departures of the latter from a t^½ dependence may be due to radiogenic heating within the mantle.