Regional variations in subsidence rate of oceanic plates: a global analysis

Abstract

A global analysis of the dependence of seafloor depth on crustal age has been performed for each large oceanic plate independently. Each plate has been divided into regions bounded by major tectonic features. A total of 32 regions have been considered. Bathymetry corrected for sediment loading has been plotted as a function of crustal age for each region. Except for three regions (western Pacific between 10°S and 40°N, North American plate between 24°N and 38°N and African plate between 10°N and 24°N) where ocean floor older than 80–100 Ma flattens with age, in other regions, depth increases linearly with age 1/2. Subsidence rate over each region has been computed by linear regression. Large variations (up to a factor 2) are reported from one region to another. Asymmetrical subsidence is also observed in a number of areas. However, the largest asymmetries are less than the regional variations in subsidence rate occurring on individual plates. Regional variations in subsidence rate appear linearly related to regional variations in ridge crest topography, shallow ridge subsiding quickly and deep ridge subsiding slowly. Hence seafloor depth subsides at a rate modulated by the value of the initial (axial) depth. This observation suggests that regional variations in subsidence rate reflect the thermal regime of the mantle beneath mid-ocean ridges rather than lateral temperature variations inside the asthenosphere involving small-scale convection.