A global analysis of mid‐ocean ridge axial topography

Abstract

Current views of mid‐ocean ridges are strongly influenced by extensive mapping of the Mid‐Atlantic Ridge and East Pacific Rise. The global picture of the mid‐ocean ridge system, particularly in the sparsely surveyed Southern Oceans, is still based primarily on underway bathymetry profiles collected over the past 40 years. This study presents a quantitative analysis of global mid‐ocean ridge morphology based on 156 of these underway bathymetric profiles, thereby allowing commonly recognized features such as axial valleys and axial ridges to be compared on a global basis. An Empirical Orthogonal Function (EOF) analysis is used to separate deterministic and stochastic components of axial morphology and to quantify the dependence of each on parameters such as spreading rate and axial depth. It is found that approximately 50 per cent of the variance in axial morphology may be described as a linear combination of five independent symmetric and anti‐symmetric modes; the remainder is considered stochastic. Maximum axial valley relief decreases with spreading rate for rates less than 80 mm yr‐1 while axial ridge relief remains relatively constant for all rates greater than 50 mm yr‐1. The stochastic component of the axial morphology, referred to as bathymetric roughness, also decreases with spreading rate for rates less than 80 mm yr‐1 and remains relatively constant at higher rates. Although both axial valley relief and bathymetric roughness near the ridge axis show a similar spreading rate dependence, they are weakly correlated at slow spreading centres. The distinct differences in morphologic variability of fast and slow spreading ridges may result from the episodicity of magmatic heat input which controls the lithospheric rheology at slow spreading ridges. These observations support the notion of a critical threshold separating two dynamically distinct modes of lithospheric accretion on mid‐ocean ridges. Copyright © 1994, Wiley Blackwell. All rights reserved