Intraplate deformation of oceanic crust near the Rio Grande Rise in the South Atlantic

Abstract

Globally, oceanic crust has relatively uniform thickness and structure compared to continental crust, with typical ocean crust being ~5–8 km thick. However, a substantial proportion of oceanic crust is thickened outside the normal range in the form of oceanic plateaus and crust affected by hotspots. The Rio Grande Rise (RGR) is the most prominent bathymetric feature in the western South Atlantic Ocean, and was thickened by activity of the Tristan hotspot. We use multichannel seismic data collected along the eastern margin of the RGR to investigate the relationship history between the thickened crust of the RGR and the adjacent normal crust. We find numerous normal faults spatially coincident with the region where oceanic crust begins to thicken from normal to RGR crust. Using crosscutting relationships and superposition, our interpretation supports protracted extensional deformation at the eastern margin of the RGR, including recent activity that appears to deform the modern seafloor. We attribute the faulting to differential subsidence linked to crustal thickness variations between the thickened RGR and ‘normal’ oceanic crust. Given the fundamental processes we attribute to the cause of faulting and the proportion of thickened oceanic crust globally, it is possible that regions of many oceanic plates experience intraplate deformation after formation.