Anomalous bathymetry, 3D edge driven convection, and dynamic topography at the western Atlantic passive margin

A series of topographic/bathymetric anomalies trend along the western passive plate margin of the North Atlantic and are characterized roughly by uplift offshore on the ocean plate and subsidence at the continental margin. The features—determined from two independent data sets—are not constant along the strike of the plate boundary, however. The anomalous topography/bathymetry is considered to be a surface dynamic response to edge driven convection in the mantle occurring at the continental margin. Three-dimensional numerical mantle flow experiments are conducted to investigate the margin-parallel and -perpendicular development of edge driven convection and dynamic topography. The flow induces a near-margin topography low and offshore bathymetry high of up to ∼1.5 km. If the thermal structure of the convection is perturbed along strike to the plate boundary, the edge driven convection cells develop instabilities with a similar ∼500 km wavelength. This causes localized peaks and saddles in the topography/bathymetry that is consistent with the observed variability of residual topography along the western side of the North Atlantic. The plate margin experiences modest thermal erosion causing dynamic topography to migrate continent-ward and slightly increasing its wavelength. Generally, though, the flow and associated topography developed into a quasi-static form relative to the passive margin over timescales of at least tens of millions of years.

Research highlights▶ Edge driven convection inducing offshore uplift and near margin deepening. ▶ Along strike variation of topography/bathymetry attributed to sub-lithospheric flow. ▶ Onshore topographic lows may be related to western Atlantic sedimentary basins. ▶ Additional possible interpretation of negative dynamic topography in Conrad et al. (2004).