A prominent positive magnetic anomaly, with amplitude as great as 1400 nT, lies along the lower slope between the northern Exmouth Plateau, characterized seismically by faulted layered reflectors, and the Argo Abyssal Plain, characterized by hyperbolic reflectors. Because the slope of the northern Exmouth Plateau is floored by continental crust, as shown by Triassic and Early Jurassic volcanics and sediments deposited before the Middle Jurassic inception of spreading in the Argo Abyssal Plain, the anomaly lies along the continent-ocean boundary (COB). To the northeast of the northern Exmouth Plateau, the anomaly, here with an amplitude no greater than 700 nT, is traced along the lower slope of the Rowley Terrace and Scott Plateau, and across the expanded continental rise north of 13°S, and indicates that the Rowley Terrace and the bulk of the Scott Plateau are continental, and that only the lower part of the rise, north of 13°S, is oceanic. In this area, an oceanic ridge rises above the adjacent breakup unconformity in the Scott Plateau to impound a deep sedimentary basin, like that impounded by the Outer Voring Plateau off Norway. The COB anomaly is modelled as a shallow two-dimensional magnetic body with rectangular cross-section and 40-80 km wide that extends up to 20 km seaward of the COB, and is interpreted as a complex of rift-related dykes in the continental crust and adjacent oceanic crust.