Asymmetric sea-floor spreading caused by ridge-plume interactions

Crustal accretion at mid-ocean ridges is generally modelled as a symmetric process. Regional analyses, however, often show either small-scale asymmetr ies, which vary rapidly between individual spreading corridors, or large-sc ale asymmetries represented by consistent excess accretion on one of the tw o separating plates over geological time spans(1-6). In neither case is the origin of the asymmetry well understood. Here we present a comprehensive a nalysis of the asymmetry of crustal accretion over the past 83 Myr based on a set of self-consistent digital isochrons(7) and models of absolute plate motion(8,9). We find that deficits in crustal accretion occur mainly on ri dge hanks overlying one or several hotspots. We therefore propose that asym metric accretion is caused by ridge propagation towards mantle plumes or mi nor ridge jumps sustained by asthenospheric flow(10,11) between ridges and plumes. Quantifying the asymmetry of crustal accretion provides a complemen tary approach to that based on geochemical(12) and other geophysical data(1 3,14) in helping to unravel how mantle plumes and mid-ocean ridges are link ed through mantle convection processes.