New apatite fission-track (AFT) ages from Heimefrontfjella and Mannefallknausane indicate that the Mesoproterozoic basement and Permian sedimentary cover rocks were heated to c. 100°C during the Mesozoic. Heating was due to the burial by up to 2000 m of Jurassic lavas at c. 180 Ma, when the area was affected by the Bouvet/Karoo hot spot. Near the developing coastline, the lava pile was quickly eroded and in part deposited on the continental shelf as pebbly and coarse-grained volcaniclastic sandstones. The AFT data indicate that farther inland the lava pile was not eroded until c. 100 Ma, and the Palaeozoic unconformity between the Mesoproterozoic basement and Permo–Carboniferous sedimentary rocks as a reference plane remained at temperatures of c. 80°C. Formation of an up to 800 m b.s.l. deep graben in from Heimefrontfjella as well as flexural uplift and rapid denudational cooling of the not extended crust from Heimefrontfjella southwards occurred at c. 100 Ma. It is speculated that a period of major plate reorganisation and new rifting at c. 100 Ma is responsible for affecting a much wider continental margin as far inland as Heimefrontfjella and producing a total relief in excess of 3500 m.